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Departments of 1 Environmental Health Sciences and 2 Pulmonary and Critical Care Medicine, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21205; and 3 Department of Pediatrics, Magee-Womens Research Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
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ABSTRACT |
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Top
Abstract
Introduction
Methods
Results
Discussion
References
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A profile of respiratory complications has been associated with the onset and development of obesity in humans. Similar phenotypes have been routinely demonstrated in genetic animal models of obesity such as the ob mouse (C57BL/6J-Lepob). The objective of the present study was to test the hypothesis that a constellation of respiratory complications are attenuated with leptin (i.e., protein product of the ob gene) replacement. Daily leptin administration during a 6-wk period was conducted to control body weight of mutant ob mice similar to genotypic control groups. During the treatment period, repeated baseline ventilatory measurements were assessed by using whole body plethysmography while quasistatic pressure-volume curves were performed to further explore the role of leptin in improving lung mechanics. Diaphragmatic myosin heavy chain (MHC) isoform phenotype was examined to determine proportional changes in MHC composition. In room air, breathing frequency and minute ventilation were significantly (P < 0.01) different among ob treatment groups, suggesting that leptin opposed the development of a rapid breathing pattern observed in vehicle-treated ob mice. Quasistatic deflation curves indicated that the lung volume of leptin-treated ob mice was significantly (P < 0.05) greater relative to vehicle-treated ob mice at airway pressures between 0 and 30 cmH2O. Diaphragm MHC composition of leptin-treated ob mice was restored significantly (P < 0.05) to resemble the control phenotype. In this genetic mouse model of obesity, the results suggested that respiratory complications associated with the obese phenotype, including rapid breathing pattern at baseline, diminished lung compliance, and abnormal respiratory muscle adaptations, are attenuated with prolonged leptin treatment.
genetic control of ventilation; lung pressure-volume curves; diaphragm myosin heavy chain composition; lung growth and development
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INTRODUCTION |
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Top
Abstract
Introduction
Methods
Results
Discussion
References
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THE IMPACT of respiratory complications associated with obesity is a threatening public health issue caused by the growing prevalence of obese humans in industrialized civilizations (e.g., Ref. 16) and the apparent link between obesity and sleep-disordered breathing (e.g., Ref. 14). Evidence from human studies (23, 25) and animal models of obesity (e.g., Refs. 31 and 34) have suggested that during both sleep and wakefulness genetic determinants confer anomalies in respiratory control mechanisms free of weight-dependent effects. When examining awake rats of four inbred strains, including two strains susceptible to obesity, Strohl et al. (31) highlighted important genetic factors to explain strain differences in breathing patterns at baseline that were independent of covarying body weight effects. In contrast, baseline ventilatory changes in obese humans have been thought to be mainly due to an increased pulmonary elastance and reductions in lung volume (e.g., Ref. 22). The weight-dependent mechanical changes imposed on the chest wall are generally accompanied by a cephalad displacement of the diaphragm and increased intra-abdominal pressure. To understand the impact of obesity on lung structure and function, one must distinguish between respiratory complications associated with increased adiposity and other intrinsic features, including genetic determinants. The present study was designed to control the development of obesity, so as to explore the residual susceptiblity to potential respiratory complications.
In the ob murine model, ventilatory anomalies included a rapid breathing pattern at baseline, which develops predominantly between 30 and 80 days of age (a time interval in which a precipitous increase in body weight occurred) (34). Localized to mouse chromosome 6 (9, 38), the ob gene mutation routinely confers an obese phenotype in C57BL/6J inbred mice with the homozygous genotype (ob/ob). Leptin, a 16.5-kb endocrine product of the ob gene, has been shown to be a powerful satiety factor that is synthesized and secreted by adipocytes (3, 11, 21). There are functionally similar effects of leptin in mice and humans (e.g., Refs. 5 and 30); these effects include a depression in food consumption, an increase in caloric expenditure, and an elevation in deep-body temperature (Tdb). In addition, leptin has been shown to play a pivotal role in the prepubertal development of reproductive functions (2, 4). We postulate that the coincident time course between the development of rapid breathing and the onset of obesity suggests a role for leptin in age-dependent changes in lung structure and function. Therefore, one aim of the present study is to focus on changes in ventilatory control at baseline in a series of ob mice in the presence or absence of leptin replacement.
These studies extend our previous findings that describe obesity-hypoventilatory traits in the ob mouse model (36) by describing the influence of leptin on the baseline breathing pattern, quasistatic pressure-volume (P-V) relationships, and diaphragmatic muscle fiber typing. The results indicate that leptin modulates the development of baseline respiratory complications associated with obesity. These data also support the hypothesis that leptin acts primarily to prevent an obesity-induced rapid breathing pattern at baseline by attenuating mechanical changes that foster reductions in lung volume. Therefore, leptin may potentially play an important role in normal lung growth and development.
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METHODS |
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Top
Abstract
Introduction
Methods
Results
Discussion
References
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Animals. Male and female C57BL/6J-Lepob homozygotes (ob) are infertile in the absence of leptin. The ob gene mutation is routinely propagated by breeding heterozygotes (ob/+) within the C57BL/6J (B6) inbred strain. That is, the offspring of ob/+ progenitors consist of homozygotes and congenic littermates (?/+) in a 25:75 ratio. In the present study, all animals, including wild-type (+/+) mice, were weaned at 21-28 days of age and were genotypically identified by Jackson Laboratory (Bar Harbor, ME) before their procurement. The animals were housed in a facility at The Johns Hopkins University; the temperature was maintained at ~21.5°C, and the light-dark cycle was 12:12 h, beginning at 0700. Ventilatory data were randomly sampled between 0900 and 1800 at chamber temperatures between 26 and 28°C. Water and mouse chow (Agway Pro-Lab RMH 1000) were provided ad libitum throughout the studies described below.
Leptin administration. When mutant and control mice were received at 28-32 days of age, the average body weight of the ob/ob mice was determined to be ~15% greater (P < 0.05) relative to age-matched control groups. On a daily basis, each animal was weighed, and an adjusted dose of recombinant murine leptin (r-metmuleptin; Amgen) was intraperitoneally administered intended to manage body weight of a subgroup of ob mice (n = 12) to resemble lean control groups. Vehicle-treated ob mice (n = 4) were administered physiologically based saline at an average volume equivalent to that for leptin-treated animals. In most cases, the time of day at which leptin administration occurred was within several hours (i.e., 1200-1600) of the natural peak in serum leptin levels (1, 30). As shown in Fig. 1, daily leptin was administered at a dose of 5 mg/kg of body weight immediately after studies to assess pretreatment ventilatory characteristics. Increases in the average daily dose of leptin occurred within weeks 1 and 2, followed by a period during which the dose required to manage body weight remained relatively constant (weeks 3 and 4). During weeks 5 and 6 of leptin treatment, the daily dose was gradually reduced.
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Whole body plethysmography. The methods used to assess ventilatory characteristics have been described in detail elsewhere (6, 34, 35). Briefly, whole body plethysmography was used in combination with a standard hypercapnic- and hypoxic-challenge protocol to assess ventilatory responses in unanesthetized, unrestrained mice. Baseline ventilatory function was assessed by computing the average of five intermittent room air measurements. Each animal was permitted to acclimate within the chamber for at least 30 min before the beginning of the protocol. Chamber temperature was maintained within the thermoneutral zone for mice (i.e., 26-28°C) and was recorded with each ventilatory measurement by using a Type-T thermocouple. Compressed air was humidified (90% relative humidity) and directed through the chamber at a flow rate of ~300 ml/min. After the animal became quiescent, breathing frequency (f), tidal volume (VT), and inspiratory time (TI) were recorded on a strip-chart recorder (Grass Polygraph, model 7D). At a constant chamber volume, changes in pressure due to inspiratory and expiratory temperature fluctuations were measured by using a differential pressure transducer (model 8510B-2, Endevco). As shown in Fig. 1, ventilatory data were repeatedly measured in leptin- and vehicle-treated animals after 3, 13, 20, 28, 35, and 42 days of treatment.
Quasistatic P-V curves.
After repeated ventilatory measurements, leptin- and vehicle-treated
ob mice at 75-85 days of age, as
well as control animals, were prepared for quasistatic P-V curves.
Animals were anesthetized with intraperitoneal injections of
pentobarbital sodium at a dose of ~70-80 mg/kg body weight.
After the trachea was cannulated and while the animal was in a supine
position, each animal was ventilated with 100% oxygen for 10 min
before the cannula was sealed with a stopcock to degas the lung (8).
Quasistatic P-V curves were immediately performed in situ, at least two
times each, with the respiratory system intact and with the thorax
widely opened. The rate of inflation and deflation was standardized by a dual infusion-withdraw pump (model 900-610, Harvard Apparatus, Dover, MA), and the airway pressure was measured by using a
differential pressure transducer (model 8510B-2, Endevco). The initial
inflation rate was controlled at ~0.5 ml/min to ensure that all lung
regions opened before being switched to a rate of 2.1 ml/min for the
remaining inflation-deflation manuevers. The limits of the inflation
and deflation airway pressures were 30 and 
5
cmH2O, respectively.
5 and 30 cmH2O, respectively, with the
respiratory system intact (13). FRC was also determined on deflation at
0 cmH2O. Compliance of both the
respiratory system intact (Crs) and lung only was computed as the slope
of the P-V relationship between 0 and 10 cmH2O on deflation. The shape of the P-V relationship was further examined by normalizing intermediate volumes for differences in TLC30.
Diaphragm myosin heavy chain (MHC) composition. Diaphragm muscle was excised from young and older groups of animals to establish age and genotypic effects. Diaphragm tissue was obtained from 7-wk-old animals which were subsequently used in other studies. In additon, diaphragm tissue was obtained from older animals at 350 days of age for the ob mice and at 480 days in the remaining genotypic classes. Ventilatory data from these groups of animals were previously reported elsewhere (34). In animals used to assess the effects of leptin, diaphragm tissue was obtained after the quasistatic P-V manuever. Each animal was anesthetized with pentobarbitol sodium (80 mg/kg) before tissue was excised, and samples were immediately frozen and stored at -70°C for subsequent classification of MHC composition.
Myosin extractions and MHC electrophoresis were performed as previously described (37). Briefly, myosin for electrophoresis was prepared by scissor-mincing the muscle tissue in a high-salt solution, pH 6.5, at 4°C for 40 min. Extracts were centrifuged, and supernatants were recovered and treated as follows. Electrophoresis of MHC isoforms was performed by using the method of Talmadge and Roy (33). Then 10 µl of supernatant were diluted (1:10) in a low-salt buffer consisting of 1 mM EDTA and 0.1% 2-mercaptoethanol and were stored overnight at 4°C to allow precipitation of myosin filaments. The filament solution was subsequently centrifuged to form a pellet, which was then dissolved in myosin sample buffer (0.5 M NaCl, 10 mM NaH2PO4, pH 7.0) followed by dilution of 1:100 in SDS sample buffer [62.5 mM Tris · HCl, 2% (wt/vol) SDS, 30% glycerol, 5% (vol/vol) 2-mercaptoethanol, and 0.001% (wt/vol) bromophenol blue at pH 6.8]. The samples were boiled for 2 min and stored at80°C.
Gels were prepared from a stock solution of 30% acrylamide that
contained 29.4% (wt/vol) acrylamide and 0.6%
N,N'methylene-bis-acrylamide (Bis). Electrophoresis was performed on slabs (18 × 16 × 0.75 mm thick) consisting of an 11.5-cm separating gel and a 4.5-cm stacking gel. Separating gels of total concentration of monomer (acrylamide + Bis) (T) = 8%, and stacking gels of T = 4% at
percentage of total monomer due to Bis (C) = 2% were used. Volumes of
myosin extract (1-3 µl) containing 500-1,000 ng of protein
per well were loaded on the gels. Electrophoresis (275 V for 3.5 h and
then 178 V for 17.5 h) was performed by using a vertical-slab gel unit (SE600, Hoefer Scientific Instruments) with a Tris-glycine-SDS running
buffer in a cold room maintained at 4°C (33). Separating gels were
silver stained.
MHC gels were analyzed by using a scanning densitometer (GS 300, Hoefer
Scientific) and densitometry software (GS 365, Hoefer Scientific) to
quantify the area under individual isoform peaks.
Data analysis.
In computing VT, the amplitude
of the inspiratory and expiratory limbs of each tidal breath were
averaged over ~15 consecutive breaths, and body temperature of each
animal was assumed to be constant at 37°C. Although the resting
Tdb was shown to differ among
treatment groups, the magnitude was within ~1-2°C (see Fig. 2B),
accounting for <5-10% error in computing baseline
VT. Minute ventilation
(
E) was calculated as the product of f
and VT.
TE was determined from total
respiratory time (Ttot) minus
TI, mean inspiratory flow was
calculated as the ratio of VT to
TI, and the respiratory duty
cycle was computed as the ratio of
TI to Ttot.
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RESULTS |
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Top
Abstract
Introduction
Methods
Results
Discussion
References
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Body weight and temperature. As shown in Fig. 2A, the average (mean ± SE) body weight of the leptin-treated ob mice during the 6-wk treatment was maintained within a range between 27.1 ± 0.6 and 30.4 ± 0.7 g. The average body weight of the control groups was within a range of 21.3 ± 0.5 to 27.9 ± 0.8 g during the same time interval. The vehicle-treated ob mice demonstrated a steady increase in body weight, reaching 51.6 ± 0.6 g by 73 days of age.
Tdb is shown in Fig. 2B for the leptin- and vehicle-treated ob mutants relative to the ?/+ control mice. Vehicle-treated ob mice demonstrated a significantly (P < 0.05) lower Tdb compared with both the leptin-treated and control mice within the first week of leptin administration.Room air ventilation.
The magnitude and pattern of breathing at baseline are illustrated in
Fig. 3. The baseline
E response in vehicle-treated ob mice was significantly
(P < 0.05) elevated during the 6-wk treatment compared with the leptin-treated
ob and control mice (Fig.
3A). There were no significant
differences in VT, but f was
significantly (P < 0.05) elevated
above the pretreatment response by 45 days of age in vehicle-treated
ob mice (Fig. 3,
B and
C, respectively). The increases in
baseline f and E were not observed in
leptin-treated ob mice. Therefore,
leptin treatment appeared to significantly
(P < 0.01) inhibit the development
of a rapid breathing pattern at baseline and the rise in
E that normally occurred in
ob mutants.
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Quasistatic P-V relationships. Figure 6 depicts lung deflation curves with and without the chest wall intact for vehicle- and leptin-treated ob mice and for each genotypic control group. The lung volume of vehicle-treated ob mice was significantly (P < 0.01) attenuated at airway pressures between 0 and 30 cmH2O compared with each of the genotypic control groups (i.e., +/+, ?/+, and ob/+). In a similar range of airway pressures, leptin-treated ob mice demonstrated significantly (P < 0.05) greater lung volumes relative to the vehicle-treated ob mice, but these volumes were still significantly (P < 0.05) less than those of the controls. There were no significant (P > 0.05) differences between groups in the percent deflation volume when volumes were normalized by TLC (data not shown). This similarity among groups indicated that the differences in absolute P-V relationships were primarily a volume-dependent effect.
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Diaphragm MHC phenotype. Table 2 shows the proportional diaphragmatic MHC composition for young and older groups of mutant and genotypic control mice. In each of the genotypic classes, an age-dependent change in the diaphragm MHC isoform composition was observed favoring a significant (P < 0.05) reduction in the percentage of MHC type IIx isoform. In addition, older ob mice demonstrated a significant (P < 0.01) increase in MHC type I composition relative to genotypic controls. This was accompanied by a significantly (P < 0.01) greater proportion of MHC type IIa and reduced proportion of MHC type IIx. The most apparent change in older ob mice was the significantly (P < 0.01) diminished percentage of MHC type IIb, to the extent that this MHC isoform was undetectable in a majority of individual samples. Because this phenotypic transition was observed in younger ob mice at ~7 wk of age, a time-dependent association corresponded to the significant change in the rapid breathing pattern at baseline (Fig. 3A).
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DISCUSSION |
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Top
Abstract
Introduction
Methods
Results
Discussion
References
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Leptin replacement in ob mice attenuates a variety of respiratory alterations, including volume-dependent lung mechanical properties and respiratory muscle adaptations coincident with a significant reduction in the development of rapid breathing at baseline. It is difficult to determine from the results whether the changes in structure and function were caused by factors associated with weight control or by a more direct effect of leptin on lung growth. The evidence suggests that there may be an interaction between both mechanisms. These results extend the obese phenotype to involve additional characteristics of respiratory alterations, such as a reduced lung compliance and an altered diaphragmatic MHC composition which favors fatigue resistance. A similar phenotypic profile, relating lung function and structure, has been characterized in morbidly obese humans (17, 20, 28, 32), although the ob mutation is rarely found in obese human populations (18).
The major effects of leptin are involved in satiety and metabolism (3,
11, 21). Leptin acts as a satiety factor and thus reduces food intake.
Leptin also acts as a metabolic factor to stimulate oxygen consumption
and elevate body temperature. In addition, the results of the present
study suggest leptin's effects influence the control of ventilation at
baseline. In vehicle-treated ob mice,
the baseline E progressively increases
during the period of 30-80 days of age, primarily due to the onset
of a rapid breathing pattern (Fig.
3C). In leptin-treated
ob mice, the magnitude and pattern of
baseline breathing are not altered from pretreatment responses and
resemble those in control ob/+ mice.
Concurrently, body weight gain is curtailed in leptin-treated
ob mice within a 3-g range and
resembles control groups by the end of the 6-wk treatment period (Fig.
2A). Consistent with previous
studies (11), body temperature in the present study is significantly
lower in the vehicle-treated ob mice
compared with leptin-treated and control groups (Fig.
2B). The time course of these
results suggests that the changes in ventilatory control at baseline
are coupled with the leptin-induced maintenance of body weight and
temperature regulation.
Because the predominant regulatory mechanism for leptin is mediated via leptin receptors in the hypothalamus (7, 10, 29), an influence on the central integration of breathing may involve a similar mechanism. The hypothesis that leptin involves a neural component is further supported by the influential effect of leptin in stabilizing mean inspiratory flow at baseline (Fig. 5). Compared with leptin-treated and control mice, vehicle-treated ob mice demonstrate a progressive and significant increase in mean inspiratory flow that implies a difference in the neural "drive" to breathe (19). However, with leptin deficiency, the 50-60% increase in ventilation (Fig. 3) occurs in the face of mechanisms that presumably lead to hypometabolism and hypothermia characteristic of ob mice. Therefore, the effect of leptin on baseline ventilation is not likely coupled with a restoration of metabolism or temperature regulation.
It is also possible that the imposition of abdominal adiposity (22) and the displacement of the diaphragm require a greater neural input per tidal breath (26). With this mechanism, the development of a phenotype with rapid breathing at baseline would accompany a diaphragmatic muscle adaptation. This implies that leptin's action in stabilizing the magnitude and pattern of baseline ventilation may involve a secondary effect mediated by leptin-induced weight control. The most dramatic change in baseline ventilation occurs between 35 and 45 days of age in vehicle-treated ob mice. During this time interval, a coincident 23% increase in body weight (i.e., from 35.4 ± 0.6 to 43.4 ± 0.7 g) develops in the leptin-deficient mice, while the rapid breathing pattern is influenced by 12 and 21% reductions in TI and TE, respectively. Therefore, the development of rapid breathing in vehicle-treated ob mice is likely due, in part, to the accelerated weight gain and the imposition of fatness on the mechanical properties of the lung and chest wall. This hypothesis is explored by performing quasistatic P-V curves in treated and control mice. Because of the decline in TE observed in vehicle-treated ob mice, we emphasize the deflation curve to illustrate group differences in compliant properties of the lung.
Effect of leptin on the lung compliance and chest wall compliance. As shown in Fig. 6, the lung volume is significantly lower at every airway pressure in vehicle-treated ob mice compared with leptin-treated and control mice. Although there are no detectable differences among the control groups, leptin-treated ob mice demonstrate significantly lower lung volumes for a given airway pressure compared with each control group. Furthermore, there are no detectable differences in lung volume between the results obtained with the respiratory system intact in comparison with the lung only. These results are consistent with previously described P-V relationships in mice; this suggests that the compliance of the relaxed chest wall of the mouse is much greater than that of the lung (15, 36). Thus the influence of exaggerated intrathoracic adiposity is mediated through an effect on the lung only. The mechanism by which the excess adipose tissue within the thorax and lung leads to decreased lung volume and compliance is not yet understood. An alternative explanation involves the imposition of abdominal fatness, thus forcing the cephalad-displaced diaphragm to restrict lung inflation and to promote lung recoil on deflation. Exploratory studies in isolated lung preparations suggest that this is not a likely explanation, because little difference is observed in the lung deflation curves between in situ and isolated lung conditions.
In human obesity, the restriction imposed on the lung by adipose tissue has been suggested to develop via a similar mechanical process. An increased elastance of the respiratory system in conscious obese individuals has been shown to involve reductions in lung volume and compliance. Respiratory system stiffening has been observed in the presence or absence of changes in chest wall compliance (20, 22, 32). This is also observed in the present results, in which the same lung volume reductions in the obese model are found with or without the intact chest wall. Furthermore, the effects of leptin appear to facilitate lung growth and development in ob mutant mice by increasing lung compliance via volume-dependent mechanisms. Although leptin restores and stabilizes the baseline ventilatory function in mutant ob mice, the 6-wk treatment protocol incompletely rejuvenates lung mechanical behavior. Future studies are required to assess whether leptin acts directly on lung growth or whether its action is permissive and limited to a weight-management factor. The possibility that leptin is involved in lung growth and development is further supported by recent evidence related to the prepubertal role of leptin in reproductive development (2, 4, 12). The rapid breathing pattern shown in morbidly obese humans is believed to be a load compensatory mechanism in response to attenuated respiratory system compliant changes. Sampson and Grassino (28) demonstrated a rapid breathing pattern accompanying an increase in inspiratory neuromuscular drive, as measured by airway occlusion pressure in 0.1 s (significant differences in VT/TI were not evident). These authors suggested that an increase in the neural "drive" was indicative of a recruitment of ancillary inspiratory muscles and departure from a predominantly diaphragmatic contribution to tidal breathing. Rochester (26) suggested that a rapid breathing pattern of obese humans was consistently associated with increased work and ventilatory drive to breathe. In the present study, we observed a similar increase in baseline inspiratory "drive" in the obese phenotype. Although the alterations in the diaphragm muscle composition of vehicle-treated ob mice suggest an adaptation to improved efficiency in terms of fatigue resistance, additional functional studies are required.Effect of leptin on the diaphragm MHC composition. The differences in diaphramatic muscle MHC composition indicate that an adaptation occurs in vehicle-treated and older untreated ob mutants. There is a significantly greater proportion of MHC type I to the total MHC phenotype, which is accompanied by a significant decrease in MHC type IIb in young and older ob mutants relative to the other genotypic classes. This shift in MHC isoform composition in ob mice would favor enhanced fatigue resistance. Powers et al. (24) showed similar age-dependent shifts in diaphragm muscle structure and function in obese Zucker rats. These investigators further suggested that the shift in MHC isoforms increased the efficiency of energy utilization and delayed fatigue. In the present study, vehicle-treated ob mutants demonstrate an increased f (i.e., animportant aspect in provoking fatigue resistance) at ~7 wk, which is coincident with the adaptive shift in diaphragmatic muscle composition. In leptin-treated ob mice, the increase in f does not occur, and the changes in diaphragmatic muscle composition are not apparent. Therefore, leptin treatment appears to oppose the remodeling of the respiratory muscle by preventing the obesity-induced rapid breathing pattern.
Evidence from the present study suggests that leptin significantly improves the rapid breathing pattern at baseline that develops in vehicle-treated ob mice. One prominent mechanism might involve the leptin-dependent improvement in reducing the abnormal mechanical load on the lung. The imposition of adipose tissue may significantly reduce lung volume and compliant properties that appear to be partially reversible with leptin treatment in ob mice. The diaphragmatic MHC composition appears to be adaptable and influenced by leptin treatment. That is, a fatigue-resistant MHC phenotype develops within 7 wk of age in vehicle-treated ob mice concurrent with the onset of rapid breathing at baseline. Leptin treatment appears to suppress the diaphragm muscle adaptation that is associated with obesity and facilitates a MHC phenotype consisting of a greater proportion of a MHC type IIx and lower proportion of the MHC type I isoform. One hypothesis considers the role leptin plays in lung growth and development. Recent evidence (12) suggests that the placenta is a significant source of leptin, which also plays a role in intrauterine and neonatal development. Because ob mice are propagated in +/+ or ob/+ dams (i.e., leptin-sufficient mice), ob/ob offspring are presumably exposed to leptin in utero. However, the absence of leptin during periods of postnatal development may irreversibly influence lung growth and development to provoke reduced lung volume and compliance. This factor (i.e., neonatal leptin deprivation) could account for the attenuated P-V relationship in leptin-treated mutants compared with the untreated control groups (Fig. 6). As indicated by differences in lung volume between leptin- and vehicle-treated ob/ob mice, leptin administration initiated at 28 days may be significant to the remaining lung growth that occurs during intermediate development. In conclusion, the volume-dependent decrease in lung compliance observed in vehicle-treated ob mice is the prominent factor causing an onset of a rapid breathing pattern at baseline. When lung volume of ob mice is restored with leptin treatment, the phenotype with rapid breathing at baseline and with the remodeling of the diaphragm does not develop.| |
ACKNOWLEDGEMENTS |
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We thank Amgen for the recombinant leptin. The invaluable technical support of Richard Rabold is also appreciated.
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FOOTNOTES |
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This study was supported by National Heart, Lung, and Blood Institute Grants HL-53700, HL-37379, and HL-51292.
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests: C. G. Tankersley, Div. of Physiology, School of Hygiene and Public Health, The Johns Hopkins Univ., 615 N. Wolfe St., Baltimore, MD 21205.
Received 24 March 1998; accepted in final form 15 July 1998.
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REFERENCES |
|---|
|
Top
Abstract
Introduction
Methods
Results
Discussion
References
|
|---|
1.
Ahren, B.,
S. Mansson,
R. L. Gingerich,
and
P. J. Havel.
Regulation of plasma leptin in mice: influence of age, high-fat diet, and fasting.
Am. J. Physiol.
273 (Regulatory Integrative Comp. Physiol. 42):
R113-R120,
1997
2.
Barash, I. A.,
C. C. Cheung,
D. S. Weigle,
H. Ren,
E. B. Kabigting,
J. L. Kuijper,
D. K. Clifton,
and
R. A. Steiner.
Leptin is a metabolic signal to the reproductive system.
Endocrinology
137:
3144-3147,
1996[Abstract].
3.
Campfield, L. A.,
F. J. Smith,
Y. Guisez,
R. Devos,
and
P. Burn.
Recombinant mouse OB protein: evidence for a peripheral signal linking adiposity and central neural networks.
Science
269:
546-549,
1995
4.
Chehab, F. F.,
M. E. Lim,
and
R. Lu.
Correction of the sterility defect in homozygous obese female mice by treatment with the human recombinant leptin.
Nat. Genet.
12:
318-320,
1996[Medline].
5.
Considine, R. V.,
M. Sinha,
M. L. Heiman,
A. Kriaugiunas,
T. W. Stephens,
M. R. Nyce,
J. P. Ohannesian,
C. C. Marco,
L. J. McKee,
T. L. Bauer,
and
J. F. Caro.
Serum immunoreactive-leptin concentrations in normal-weight and obese humans.
N. Engl. J. Med.
334:
292-295,
1996
6.
Drorbaugh, J. E.,
and
W. O. Fenn.
A barometric method for measuring ventilation in newborn infants.
Pediatrics
16:
81-86,
1955
7.
Fei, H.,
H. J. Okano,
C. Li,
G. Lee,
C. Zhao,
R. Darnell,
and
J. M. Friedman.
Anatomic localization of alternatively spliced leptin receptors (Ob-R) in mouse brain and other tissues.
Proc. Natl. Acad. Sci. USA
94:
7001-7005,
1997
8.
Frazer, D. G.,
and
K. C. Weber.
Trapped air in ventilated excised rat lungs.
J. Appl. Physiol.
40:
915-922,
1976
9.
Freidman, J. M.,
R. L. Leibel,
D. S. Siegel,
J. Walsh,
and
N. Bahary.
Molecular mapping of the mouse ob mutation.
Genomics
11:
1054-1062,
1991[Medline].
10.
Glaum, S. R.,
M. Hara,
V. P. Bindokas,
C. C. Lee,
K. S. Polonsky,
G. I. Bell,
and
R. J. Miller.
Leptin, the obese gene product, rapidly modulates synaptic transmission in the hypothalamus.
Mol. Pharmacol.
50:
230-235,
1996[Abstract].
11.
Halaas, J. L.,
K. S. Gajiwala,
M. Maffei,
S. L. Cohen,
B. T. Chait,
D. Rabinowitz,
R. L. Lallone,
S. T. Burley,
and
J. M. Friedman.
Weight-reducing effects of the plasma protein encoded by the obese gene.
Science
269:
543-546,
1995
12.
Hoggard, N.,
L. Hunter,
J. S. Duncan,
L. M. Williams,
P. Trayhurn,
and
J. G. Mercer.
Leptin and leptin receptor mRNA and protein expression in the murine fetus and placenta.
Proc. Natl. Acad. Sci. USA
94:
11073-11078,
1997
13.
Koo, K.,
D. E. Leith,
C. B. Sherter,
and
G. L. Snider.
Respiratory mechanics in the normal hamsters.
J. Appl. Physiol.
40:
936-942,
1976
14.
Kripke, D. F.,
S. Ancoli-Israel,
M. R. Klauber,
D. L. Wingard,
M. J. Mason,
and
D. J. Mullaney.
Prevalence of sleep-disordered breathing in ages 40-64 years: a population-based survey.
Sleep
20:
65-76,
1997[Medline].
15.
Leith, D. E.
Comparative mammalian respiratory mechanics.
Physiologist
19:
485-510,
1976[Medline].
16.
Lewis, C. E.,
D. E. Smith,
D. D. Wallace,
O. D. Williams,
D. E. Bild,
and
D. R. Jacobs.
Seven-year trends in body weight and associations with lifestyle and behavioral characteristics in black and white young adults: the CARDIA study.
Am. J. Public Health
87:
635-642,
1997
17.
Lourenço, R. V.
Diaphragm activity in obesity.
J. Clin. Invest.
48:
1609-1614,
1969.
18.
Maffei, M.,
M. Stoffel,
M. Barone,
B. Moon,
M. Dammerman,
E. Ravussin,
C. Bogardus,
D. S. Ludwig,
J. S. Flier,
M. Talley,
S. Auerbach,
and
J. M. Freidman.
Absence of mutations in the human Ob gene in obese/diabetic subjects.
Diabetes
45:
679-682,
1996[Abstract].
19.
Milic-Emili, J., and M. M. Grunstein. Drive and
timing components of ventilation.
Chest 70 Suppl.: S131-S133, 1976.
20.
Naimark, A.,
and
R. M. Cherniack.
Compliance of the respiratory system and its components in health and obesity.
J. Appl. Physiol.
15:
377-382,
1960
21.
Pelleymounter, M. A.,
M. J. Cullen,
M. B. Baker,
R. Hecht,
D. Winters,
T. Boone,
and
F. Collins.
Effects of the obese gene product on body weight regulation in ob/ob mice.
Science
269:
540-543,
1995
22.
Pelosi, P.,
M. Croci,
I. Ravagnan,
M. Cerisara,
P. Vicardi,
A. Lissoni,
and
L. Gattinoni.
Respiratory system mechanics in sedated, paralyzed, and morbidly obese patients.
J. Appl. Physiol.
82:
811-818,
1997
23.
Pillar, G.,
and
P. Lavie.
Assessment of the role of inheritance in sleep apnea syndrome.
Am. J. Respir. Crit. Care Med.
151:
688-691,
1995[Abstract].
24.
Powers, S. K.,
G. A. Farkas,
H. Demirel,
J. Coombes,
L. Fletcher,
M. G. Hughes,
K. Hodge,
S. L. Dodd,
and
E. H. Schlenker.
Effects of aging and obesity on respiratory muscle phenotype in Zucker rats.
J. Appl. Physiol.
81:
1347-1354,
1996
25.
Redline, S.,
T. Tosteson,
P. V. Tishler,
M. A. Carskdon,
and
R. P. Millman.
Studies in the genetics of obstructive sleep apnea.
Am. Rev. Respir. Dis.
145:
440-444,
1992[Medline].
26.
Rochester, D. F.
Respiratory muscles and ventilatory failure: 1993 perspective.
Am. J. Med. Sci.
305:
394-402,
1993[Medline].
27.
Rosenthal, M.,
J. Roth,
B. Storr,
and
E. Zeisberger.
Fever response in lean (Fa/) and obese ( fa/fa) Zucker rats and its lack to repeated injections of LPS.
Physiol. Behav.
59:
787-793,
1996[Medline].
28.
Sampson, M. G.,
and
A. E. Grassino.
Load compensation in obese patients during quiet tidal breathing.
J. Appl. Physiol.
55:
1269-1276,
1983
29.
Schwartz, M. W., R. J. Seeley, L. A. Campfield, P. Burn, and D. G. Baskin.
Identification of targets of leptin action in rat hypothalamus.
J. Clin. Invest. 1101-1106, 1996.
30.
Sinha, M. K.,
J. P. Ohannesian,
M. L. Heiman,
A. Kriaugiunas,
T. W. Stephens,
S. Magosin,
C. Marco,
and
J. F. Caro.
Nocturnal rise in lean, obese, and non-insulin-dependent diabetes mellitus subjects.
J. Clin. Invest.
97:
1344-1347,
1996[Medline].
31.
Strohl, K. P.,
A. J. Thomas,
P. St. Jean,
E. H. Schlenker,
R. J. Koletsky,
and
N. J. Schork.
Ventilation and metabolism among rat strains.
J. Appl. Physiol.
82:
317-323,
1997
32.
Suratt, P. M.,
S. C. Wilhoit,
H. S. Hsiao,
R. L. Atkinson,
and
D. J. Rochester.
Compliance of the chest wall in obese subjects.
J. Appl. Physiol.
57:
403-407,
1984
33.
Talmadge, R. J.,
and
R. R. Roy.
Electrophoretic separation of rat skeletal muscle myosin heavy-chain isoforms.
J. Appl. Physiol.
75:
2337-2340,
1993
34.
Tankersley, C.,
S. Kleeberger,
B. Russ,
A. Schwartz,
and
P. Smith.
Modified control of breathing in genetic (ob/ob) obesity.
J. Appl. Physiol.
81:
716-723,
1996
35.
Tankersley, C. G.,
R. S. Fitzgerald,
and
S. R. Kleeberger.
Differential control of ventilation among inbred strains of mice.
Am. J. Physiol.
26l (Regulatory Integrative Comp. Physiol. 30):
R1371-R1377,
1994.
36.
Tankersley, C. G.,
S. R. Kleeberger,
R. T. Rabold,
and
W. A. Mitzner.
Genetic determinants influence the pressure-volume relationships of the lung in inbred mice (Abstract).
Am. J. Respir. Crit. Care Med.
153:
A863,
1996.
37.
Watchko, J. F.,
M. J. Daood,
G. C. Sieck,
J. J. LaBella,
B. T. Ameredes,
A. P. Koretsky,
and
B. Wieringa.
Combined myofibrillar and mitochondrial creatine kinase deficiency impairs mouse diaphragm isotonic function.
J. Appl. Physiol.
82:
1416-1423,
1997
38.
Zhang, Y,
R. Proenca,
M. Maffei,
M. Barone,
L. Leopold,
and
J. M. Friedman.
Positional cloning of the mouse obese gene and its human homologue.
Nature
372:
425-432,
1994[Medline].
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) or vehicle (
) treatment in
ob mice on body weight
(A) and deep-body temperature
(B) relative to congenic littermate
(?/+; 
) and wild-type homozygote (+/+; 
) control groups. Values
are means ± SE. 
Significantly attenuated deep-body
temperature in vehicle-treated ob mice
compared with leptin-treated ob and
control mice, P < 0.05.
, Controls (ob/+).
A: minute ventilation;
B: tidal volume;
C: frequency. Values are means ± SE. * Significant difference from pretreatment
response, P < 0.05;
