Journal of Applied Physiology AJP: Gastrointestinal and Liver Physiology
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J Appl Physiol 87: 1253-1259, 1999;
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Vol. 87, Issue 4, 1253-1259, October 1999

INVITED REVIEW
Growth hormone restores aged diaphragm myosin composition and performance after chronic undernutrition

Bill T. Ameredes1, Jon F. Watchko2, Monica J. Daood2, J. Fernando Rosas3, Michael P. Donahoe4, and Robert M. Rogers4

1 Department of Cell Biology and Physiology, 2 Magee Womens Research Institute, 3 Children's Hospital of Pittsburgh, and 4 Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

The effects of growth hormone (GH) on diaphragm muscle myosin heavy chain (MHC) composition and mechanical performance were investigated in Fischer 344 male rats aged to senescence (24.5 mo of age). Chronic undernutrition (UN), refeeding (RF), and RF+GH were compared with ad libitum feeding by using a model of UN that produced a 50% decrease in body weight over a 12-mo period. The effect of aging was assessed by comparing MHC composition of ad libitum-fed rats at 12 and 24.5 mo of age. At senescence, significant decreases in slow type I (-23%) and fast type IIA (-31%) MHC had occurred with aging. Conversely, UN over this aging period increased types I (32-73%) and IIA (22-23%) MHC and decreased fast types IIB (32-54%) and IIX (30-31%) MHC. RF and RF+GH reversed these shifts back toward control values. At senescence, maximal specific force, maximal velocity, and specific power capacity were not different across treatment groups. During repetitive isotonic contraction trials, the diaphragms of UN rats maintained power production over time (54% of initial power at 60 s), whereas the power production of diaphragms of ad libitum-fed rats fell to 0% (P < 0.05). In comparison with UN rats, the diaphragms of RF and RF+GH rats produced 23 (not significant) and 11% (P < 0.05) of initial power, respectively, suggesting that RF+GH treatment restored performance characteristics after UN. We conclude that RF+GH can reverse alterations in MHC composition and mechanical performance produced by chronic UN in the aged rat diaphragm.

Fischer 344 rats; fatigue; force; power; velocity


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

CHRONIC ILLNESS such as cancer and end-stage chronic obstructive pulmonary disease (COPD) can result in cachexia, characterized as poor nutrition with loss of muscle mass, or sarcopenia (4, 7, 31). The resultant decrements in limb and respiratory muscle mass and performance are poorly responsive to nutritional repletion (7). The use of anabolic hormones, such as growth hormone (GH), has been proposed in an effort to enhance the muscle recovery process (4, 7, 31). Indeed, one study has shown that GH supplementation improved respiratory muscle strength in underweight COPD patients (20). However, the specific effects of GH administration on mammalian respiratory muscle form and function in the setting of aging and chronic undernutrition (UN) remain poorly understood.

Prior studies of UN, in which food restriction in animals was used, have documented alterations of respiratory muscle phenotype and function (2, 16, 17, 22, 25). Among the changes in diaphragm muscle (Diam) phenotype have been significant decrements in types IIB and IIX (fast) fiber cross-sectional area (CSA), with no change in fiber-type frequency (16, 17, 22, 25). These changes are suggestive of reductions in types IIB and IIX fiber myosin and other cell components. Moreover, one study (16) indicated that administration of GH, in conjunction with refeeding (RF) after chronic UN, restored types IIB and IIX fiber CSA. However, the percent composition of myosin heavy chain (MHC) protein of the Diam has not been assessed previously, particularly in models of long-lasting UN (>9 wk) or in response to GH administration.

With regard to UN-induced changes in Diam muscle functional characteristics, increased relaxation rates of contraction have been reported (2, 22, 25), suggestive of slowing and consistent with the reductions of types IIB and IIX fiber CSA mentioned above. However, these studies measured function by using isometric (nonshortening) contractions (2, 17, 22, 25), which are unlike the shortening contractions typically produced by the Diam. Thus no data exist documenting the chronic-UN-induced changes in dynamic contractile properties of the Diam coupled with possible shifts in MHC composition. The effects of GH administration in this setting are similarly unknown.

Therefore, the purpose of the present study was 1) to determine the MHC composition of the aged Diam with chronic UN followed by RF and GH administration and 2) to determine the response of the aged Diam muscle during shortening contractions under these conditions. The mechanical measures included shortening displacement, velocity of shortening, and power production, assessed with isotonic afterloaded contractions, in vitro. The hypothesis was that GH was an important cofactor in recovery of muscle effects in this model of cachexia and RF with aging. Thus, in conjunction with RF, GH would produce reversals of Diam MHC shifts and functional alterations produced by chronic UN.


    METHODS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

General. The animal care and nutrition protocol was approved by the University of Pittsburgh Institutional Animal Care and Use Committee and conformed to the National Institutes of Health guidelines given in Guide for the Care and Use of Laboratory Animals [DHEW Publ. No. (NIH) 86-23, Revised 1985, Office of Science and Health Reports, DRR/NIH, Bethesda, MD 20892]. Briefly, adult male Fischer 344 rats (delivery wt, 200-224 g; approx. age, 2 mo) were fed a standard diet of Purina rat chow ad libitum and were weighed twice per week over the course of a 9-mo period from the delivery date. At that time, they achieved a body mass of ~375 g.

Dietary regime. With achievement of the average body mass of 375 g, the average daily food consumption (ADFC) for each rat was measured over a period of 1 wk. One month later, the animals were placed randomly into one of two feeding groups: a control group that continued to be fed ad libitum throughout the remainder of the study and an UN group that was fed 50% of their ADFC for a period of 7.5 mo. At the end of this period, the rats were 19.5 mo of age, and the UN group was further partitioned into three groups. One group was refed ad libitum for the remainder of the study while a second group was refed and was administered GH (Protropin, Genentech), injected intraperitoneally (1 mg/day), for the remainder of the study. This dose was chosen on the basis of a study in which 1 mg/day GH was found to produce increases in RF rat diaphragm muscle types IIB and IIX fiber CSA and a significant increase in circulating insulin-like growth factor I (IGF-I) (16). A third group remained undernourished at 50% ADFC. Twenty-four and one-half months was chosen as the end point of the study, because it fell within the span of time (21-26 mo of age) when ~70% of male Fischer 344 laboratory rats have been reported to die when fed ad libitum and therefore were considered senescent (29). Food consumption for the UN group at 24.5 mo of age remained at 50% of control (P < 0.05) while the control, RF, and RF+GH groups averaged 15-19 g/day (not significant). On the basis of this dietary regime, Diam was sampled at 12, 19.5, and 24.5 mo of age, corresponding to times just before initiation of UN, just before initiation of RF/GH administration, and the end of the study, respectively.

Diam sampling. As described previously (2), all rats were anesthetized with pentobarbital sodium (30 mg/kg ip) and shaved, and the Diam was excised surgically en bloc. At 19.5 mo of age, the in situ length of the central costal Diam was measured from the costal margin to the central tendon before excision and subsequent processing for MHC analysis, as described below. The excised Diam was cut into two hemidiaphragms, one of which was cut further into rectangular muscle segments (2-3 mm wide) such that a portion of the central tendon and the rib attachment were preserved. Segments from the costal central one-third of this hemidiaphragm were used for the contractile function experiments, performed at 24.5 mo of age. The other hemidiaphragm was trimmed of bone, fat, and connective tissue and then was blotted, weighed, and processed as described in MHC and protein analyses.

Diam mechanics. A fine, short (<= 2-cm) stainless steel wire was attached to each Diam segment, by using a small piece of foil affixed with cyanoacrylate to the central tendon, and the segment was mounted in the experiment bath by a clamp placed on the attached rib, followed by connection to a muscle ergometer (model 300B, Cambridge). The ergometer was coupled to a rapid digital storage oscilloscope (model DRO1604, Gould), allowing signal resolution of <= 500 µs. The bath was recirculated with oxygenated (95% O2-5% CO2, solution PO2 = 585 Torr) physiological saline solution (37°C) containing the following (in mM): 135 Na+, 5 K+, 2 Ca2+, 1 Mg2+, 121 Cl-, 25 HCO-3, 11 glucose, 0.3 glutamic acid, 0.4 glutamine, 5 N,N'-bis(2-hydroxylethyl)-2-aminoethanesulfonic acid buffer, and 0.008% d-tubocurarine chloride, included to remove neuromuscular junction fatigue from consideration in the subsequent fatigue experiments. The electrical stimuli producing contractions were delivered directly to the muscle segment as an electrical field stimulus by using a stimulator coupled to a current amplifier, delivering 250 mA of peak current across the segment via two platinum plate electrodes. Optimal muscle length (Lo) of the Diam segments was set by assessment of the length-tension relationship in which Lo was taken as the length at which isometric tension was maximized in response to rapid rectangular stimulus eliciting a twitch contraction (0.2-ms pulse at supramaximal current). Physical characteristics of the Diam segments studied under these conditions in vitro are shown in Table 1. At the end of the experiments, the muscle segments were removed from the bath, trimmed of fat and connective tissue, blotted, and weighed. Muscle CSA was obtained by using the muscle segment weight divided by the product of muscle density (1.056 g/cm3) and the measured Lo value (2). These segments were snap frozen in liquid nitrogen-cooled isopentane and stored at -80°C for later MHC analysis.

                              
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  		Table 1.   Physical characteristics of rat Diam hemidiaphragms and segments

Maximal tetanic isometric tension (Po) at Lo was produced by using 150-Hz stimulus train frequency delivered over 1 s. Isotonic afterloaded shortening contractions were elicited beginning at Lo by using the same stimulus frequency. A computer program (Labview) drove the ergometer to hold the afterload constant during an isotonic contraction over a range of 3-90% of Po. Typically, 8-10 afterloads were used, separated by 10% load intervals from 10-100% of Po. Contraction force and velocity signals were recorded digitally, at a frequency of 100 Hz. Force-velocity relationships for each bundle were obtained by using digitized isotonic and isometric contraction data, from which instantaneous velocity and load were obtained. Instantaneous velocity was assessed by using a maximum slope method, fitted to the initial shortening transient, in the 5- to 30-ms time domain. Load and velocity values were then fitted to a hyperbolic relationship by using an iterative, least squares regression method, as previously described (1). Velocity values were expressed as both distance shortened per unit time and as Lo shortened per second (Lo/s). Instantaneous power production was calculated as the product of load times instantaneous velocity and was expressed as unitary power, as specific power (power/muscle CSA), and as a fraction of maximal power development. Maximal instantaneous power with isotonic shortening typically occurred at an afterload of 0.30 · Po, as expected from studies in other muscles at 37°C (30).

In an attempt to put the muscle segment results into perspective with regard to the whole costal Diam, we estimated whole muscle force and power production by using measured force, length, and CSA values from the segments and hemidiaphragm weight values. A simple, three-compartment model was constructed for each hemidiaphragm, in which the assessed segment represented a portion of the central one-third of the muscle. The shape of the whole costal diaphragm was modeled as a crescent composed of two symmetrical center-aligned hemispheres, offset so that the arcs intersected to represent the lateral costal margins. An incomplete chord placed in the central one-third of the crescent, with a length equal to the measured Lo, determined the distance between the outer arcs of the hemispheres. As shown in Table 1, this length was not different from costal Diam length in situ, nor did it vary across nutritional treatment groups; therefore, we considered it to be accurate for these purposes. Two critical assumptions were that the muscle compartments within any portion of the diaphragm exerted force as a proportion of their CSA and that muscle thickness, as represented by Diam segment thickness measured at Lo, was constant across the diaphragm.This enabled us to calculate whole muscle CSA and scale whole muscle force, on the basis of measured specific force produced by the Diam segment. Although not perfect assumptions, because of the slightly irregular attachment profile and conformation of the costal diaphragm, this approach allowed us to obtain some theoretical information about alterations in whole muscle mechanics on the basis of our sample results in a muscle with a complex structural design.

Fatigue protocol. Fatigue of Diam segments was induced by using a modified Burke-type fatigue protocol (3), with 2 min of repetitive isotonic tetanic contractions at 40-Hz stimulus frequency and a stimulus duty cycle of 0.4 (560-ms train duration/1,400-ms total period). This paradigm was chosen to produce measurable fatigue quickly, with a duty cycle considered optimal for diaphragm contractile activity (13). The afterload was set to P/Po = 0.30, where P is afterload, with shortening occurring from an initial length of Lo. This afterload was chosen because it typically produces contractions of maximal power in this preparation (28). Fatigue was assessed as changes in muscle shortening over time during the contraction trial. Fatigue-resistance indexes were calculated as ratios of shortening at specific times to initial values.

MHC and protein analyses. MHC isoform composition analyses were performed on muscle homogenates from individual rats in each group. MHC isoforms were separated from myosin extracts by polyacrylamide gel electrophoresis, as previously described (2). Figure 1 shows a typical separation of diaphragm MHC isoforms obtained in this study. These data were used to determine the relative contributions of individual isoforms to their respective total MHC complements within the muscle. Total protein concentrations were measured on separate samples of muscle homogenates by using the method of Lowry et al. (18).


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  		Fig. 1.   Photograph of SDS-PAGE gel showing diaphragm muscle myosin heavy chain isoform band separation. Shown are myosin heavy chain bands for types I, IIA, IIB, and IIX isoforms. Groups are control (C; ad libitum fed), undernourished (UN), refed (RF), refed + growth hormone administration (RF+GH) at 24.5 mo of age.

Statistics. One-way ANOVA (SigmaStat, Jandel) was used to compare variables within and between treatments when the rats were aged 12, 19.5, and 24.5 mo; P < 0.05 was considered as significant. A repeated-measures ANOVA was performed on the muscle performance data to determine whether significant differences (P < 0.05) were present within and between experiments; Student-Newman-Keuls post hoc test was used to compare these variable values between groups at discrete times. The ANOVA main factors were "nutritional treatment" and "time," which were considered to indicate the respective variation between treatment groups and the variation in these data with respect to contraction trial time, respectively. The crossed factor of "nutritional treatment × time" was considered to indicate the relative variation in the pattern of fatigue. The general linear model of these ANOVAs allowed compensation for unequal sample numbers between groups through sample number weighting of expected mean square values calculated for each group.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Body weight. Respective body weights at 19.5 mo of age in control and UN groups were 440 ± 9 and 199 ± 7 g (P < 0.05). Final body weights at 24.5 mo of age averaged 418 ± 9, 213 ± 12, 399 ± 12, and 433 ± 12 g, in control, UN, RF, and RF+GH groups, respectively (P < 0.05). These data indicated that the desired target of 50% body weight difference between the UN and control groups was achieved and maintained.

Diam characteristics. As shown in Table 1, Lo of Diam segments in vitro was similar across all treatment groups. Average central costal length of the Diam in situ was 21-22 mm, and it was not different between nutritional groups or compared with Lo of the Diam segments in vitro. However, Diam mass, CSA, and protein concentration were decreased significantly by UN in both hemidiaphragms and muscle segments. These decrements were subsequently reversed with RF and RF+GH. At 19.5 mo of age, average central costal Diam segment mass was 33 ± 2 vs. 18 ± 1 mg (P < 0.05) and CSA was 1.4 ± 0.1 vs. 0.8 ± 0.1 mm2 (P < 0.05) in control and UN groups, respectively. At 24.5 mo of age, segment mass for respective control, UN, RF, and RF+GH groups was 56 ± 10, 30 ± 2 (P < 0.05), 47 ± 7, and 56 ± 7 mg; CSA was 2.3 ± 0.4, 1.3 ± 0.1 (P < 0.05), 1.9 ± 0.3, and 2.4 ± 0.5 mm2. Although the decrement in UN group muscle segment CSA was likely due to the decrement in mass, it cannot be attributed to the UN treatment alone, because of variability in muscle segment size produced with surgical sectioning. However, that this same mass effect was observed in the hemidiaphragm favors a probable treatment effect within the muscle segments.

MHC composition. Figure 2 indicates the average percent MHC composition of the central costal Diam, as represented by the muscle segments taken from this area. Control Diam types I and IIA MHC composition in this region significantly declined with aging, from 12 to 24.5 mo of age (P < 0.05). A concomitant incremental trend in type IIB MHC with aging also was suggested (not significant). Types I and IIA MHC were significantly increased with UN, at 19.5 and 24.5 mo of age, whereas type I MHC was significantly decreased and was restored with both RF and RF+GH at 24.5 mo (P < 0.05). Types IIB and IIX MHC were significantly decreased with UN at 19.5 and 24.5 mo, respectively. Reversals of the UN-dependent decrements were suggested by the nonsignificant increments in types IIB and IIX MHC with RF and RF+GH.


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  		Fig. 2.   Myosin heavy chain (MHC) percent composition of central costal diaphragm with rat age and treatment. Values are means ± SE; n = 7 rats for C group at age 12 mo, and other n values are as in Table 1. A: type I MHC. B: type IIA MHC. C: type IIB MHC. D: type IIX MHC. * P < 0.05 compared with control group. + P < 0.05 compared with UN group.

Mechanical characteristics. Table 2 shows the mechanical characteristics measured in central costal Diam segments in vitro from each treatment group at 24.5 mo of age. Specific maximal isometric force (i.e., Po) produced by Diam segments was slightly greater with UN but was estimated to be lower for the whole muscle (estimated Po = 6 ± 1 vs. 8 ± 1 N; P < 0.05). This difference was reversed in the RF+GH group (10 ± 1 N; P < 0.05), whereas RF alone was not different from control (8 ± 1 N). Maximal velocity development was not different across groups. Specific maximal power development of the segments also was similar across groups but was estimated to be lower in the UN group (estimated specific maximal power development = 127 ± 9 vs. 200 ± 32 mW; P < 0.05), not different with RF alone (158 ± 33 mW), and subsequently increased in the RF+GH group (247 ± 24 mW; P < 0.05). Examples of force-velocity-power curves emphasizing these differences are shown in Fig. 3, in which points are represented from sample UN, RF, and RF+GH Diam segments, compared with the same control Diam. These sample relationships suggest a decrement in whole muscle power with UN that was restored with RF+GH.

                              
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  		Table 2.   Force, velocity, and power of diaphragm muscles at 24.5 mo of age



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  		Fig. 3.   Force-velocity-power relationships for individual diaphragms of UN, RF, and RF+GH rats (open symbols), compared with the same diaphragm of control rats (solid symbols) in each case, at 24.5 mo of age. A: control vs. UN. B: control vs. RF. C: control vs. RF+GH. Power values are estimated whole muscle values, based on muscle segment measurements, as described in text.

Fatigue characteristics. Mean performance values for the shortening Diam segments, indicated as the fatigue resistance index for power development, are shown in Fig. 4. The ANOVA main factors of nutritional treatment and time were significant, indicating that there were differences in relative power development between groups and that significant fatigue, as a loss of power over time, had occurred. The crossed factor of nutritional treatment × time also was significant, indicating a difference in the patterns of power loss over time. Post hoc analysis revealed that power development of the UN group was greater at 30 and 60 s of contractions, compared with the control and RF+GH group, but was not different from the RF group.


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  		Fig. 4.   Loss of power over time with repetitive contractions, shown as fatigue resistance index (FRI = Wt/Wi) means for each group, measured in diaphragm muscle segments at 24.5 mo of age. Values are means ± SE. W, power; t, specified time; i, initial. * P < 0.05 compared with control. + P < 0.05 compared with RF+GH group.


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

The main findings of this study were 1) a significant decrease in types I and IIA MHC of the Diam with aging into senescence; 2) a significant increase in types I and IIA MHC of the Diam with UN during this same aging period, followed by restoration of type I MHC with RF and RF+GH treatments; and 3) greater Diam fatigue resistance with UN, which was reversed with RF+GH.

MHC shifts. UN produced relative increases in types I and IIA MHC and relative decreases in types IIB and IIX MHC of the Diam. The reestablishment of control levels of Diam type I MHC composition observed with RF+GH (Fig. 2) was suggestive of a reversal of the effects of UN. Because our methods employed quantification of the relative MHC composition of the muscles, it is unknown whether these shifts occurred because of increases in the amounts of types I and IIA MHC, decreases in the amounts of types IIB and IIX MHC, or "switching" (14) of existing types IIB and IIX to types I and IIA isoforms. Decreased amounts of types IIB and IIX MHC is one possibility, perhaps due to protein catabolism that occurs with food restriction of long duration (19). The significant decrement in UN Diam protein concentration (Table 1) and prior observations of UN-induced decreases in Diam types IIB and IIX fiber CSA are consistent with this possibility (16, 17, 22, 25). Switching of MHC isoforms also is likely through hormone-mediated shifts toward slower isoforms (14). The fact that nearly 15% of normal rat Diam fibers coexpress different MHC isoforms (26) suggests some inherent plasticity in MHC composition, supporting the possibility that MHCs could be switched under extreme adaptive circumstances. However, we have suggested previously (2) that this will likely remain unknown until reliable quantitative methods are developed to determine the absolute, as opposed to the relative, amount of type-specific MHC within muscles. Whatever the explanation may be, the UN-dependent increases in types I and IIA MHC composition of the Diam may be fortuitous, because they are characteristic of slower muscle fibers that rely on efficient oxidative processes for the energy of contraction (24, 26). Thus a shift toward predominance of MHC isoforms and/or fibers associated with efficient energetic processes, in the face of declining energy substrates, might be an advantageous adaptation to chronic UN.

Over the duration of the study, the MHC profile of the central costal Diam of ad libitum-fed control rats underwent an age-related shift, with significant reductions in the percentage of types I and IIA MHC from 12 to 24.5 mo of age. Type IIB MHC also showed a trend toward increase over this time period. We have observed similar age-related shifts in a previous study of this gender and strain, from 11.5 to 17 mo of age (2). An increase in Diam type IIB MHC also has been reported in senescent male Fischer 344 rats (11, 21), as have decrements in type IIA MHC (21). However, those studies did not show decrements in Diam type I MHC. We have no explanation for these differences between studies; however, they may be due to a complex multiphasic continuum of MHC composition over the life span of the animal (2). They also may be due to differences in animal sources and housing (10), which are difficult factors to compare accurately between studies. In general, we interpret our Diam MHC shifts with aging to be consistent with prior studies.

Functional changes. The increased fatigue resistance of the shortening UN Diam, and the subsequent reversal of this effect with RF+GH (Fig. 4), is reflective of the idea that chronic UN resulted in MHC and performance shifts consistent with production of an energy-efficient, less fatiguable muscle phenotype. Consideration of these MHC shifts, in conjunction with the fact that RF alone did not restore these fatigue properties, suggests a role for GH administration in reestablishment of Diam functional properties in this model. However, as suggested by the estimated whole muscle power of the UN Diam, production of a less fatiguable muscle may not be so desirable, if the compromise is a significant decline in power capacity. Because the Diam can be considered as primarily a volume-displacement or flow generator, through its ability to shorten against inspiratory and expiratory loads, it necessarily requires that power capacity be maintained for the maintenance of respiratory function. Thus measures of specific force, velocity, and power in muscle segments may not reflect the critical alterations in whole Diam performance capacity that may compromise its normal function. This dilemma is reflected in the fact that the muscle CSA normalizations typically employed in these types of studies may mask the actual functional deficits, because decrements in force and CSA occur simultaneously, typically resulting in little or no change in specific force or power (Table 2). If the loss of cross-bridge-containing MHCs indeed occurs with chronic UN, as suggested by fiber CSA studies (16, 17, 22, 25), it stands to reason that the Diam loses force, and therefore power-generating, units. If chronic UN promotes Diam MHC switching (14), then our data suggest that MHCs with slower, less powerful cross bridges and kinetics likely become more prevalent, again resulting in power and force capacity diminutions. Thus either of these UN-induced events should result in significant decrements of whole muscle power capacity, as suggested by our estimates.

Role of GH. Because GH is 1) one of the most important protein anabolic agents in the body (8), 2) essential for protein synthesis throughout life (8), 3) shown to be decreased with aging (5), and 4) shown to reverse catabolic states (4), its therapeutic use in cachectic situations has been of interest in recent years (4, 7). Accordingly, one might also expect that GH administration would reverse some of these changes, as suggested by a study reporting that GH supplementation improved limb muscle strength in underweight COPD patients (20). Our results are consistent with these ideas, because of our observation of MHC shifts and significant decreases in Diam mass in the UN rats that were reversed with RF and RF+GH.

One potentially important factor in this hormonal scheme of muscle phenotype regulation is IGF-I. IGF-I is the active agent derived from GH and is a mediator of GH anabolic effects (6); it is also known to produce significant hypertrophy and increases in MHC content in skeletal myofibers (29). IGF-I levels also fall with aging (5) and UN (16, 27) and have been implicated in the decrement of protein synthesis capacity reported under these conditions (4, 23). The changes in Diam mass with UN in the present study are suggestive of a role for IGF-I, supported by previous evidence that IGF-I was significantly decreased with chronic UN in this same gender and strain (16). Furthermore, GH is a potent stimulus for IGF-I production (27). Thus an increase in circulating IGF-I with RF+GH (16) is a likely factor possibly promoting the reversal of UN-induced changes observed in the present study. Recovery of the functional characteristics with RF+GH suggests that GH administration was a necessary treatment, perhaps acting solely or synergistically through reestablishment of IGF-I levels (16).

We do not know the exact nature of the interaction between GH and IGF-I under these conditions. It is also possible that decreased activity of the thyroid axis with chronic UN may have resulted in a decrement in IGF-I production (15, 19, 27). However, the simple linkage of decreased thyroid hormone levels to rat skeletal and respiratory muscle MHC profile and performance has not been uniform (9, 12, 14), possibly depending on the technique utilized to induce hypothyroidism. For instance, severe acute hypothyroidism induced with propylthiouracil resulted in decrements in Diam specific force and velocity (12), which were not observed in the present study. Thus the fact that we observed significant increments in both types I and IIA MHC and an decrement in type IIX MHC with chronic severe UN suggests that several hormonal factors may have been involved.


    ACKNOWLEDGEMENTS

The authors gratefully acknowledge the technical support of Frank E. Phelps and Mark Barsic in the performance of these studies. The human recombinant growth hormone (Protropin) used in these studies was a generous research gift from Genentech.


    FOOTNOTES

This work was supported by American Lung Association Research Grant RG-196-N. B. T. Ameredes was a Love Pulmonary Scholar, through the support of the George H. Love Pulmonary Foundation (Pittsburgh, PA).

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 and other correspondence: B. T. Ameredes, Div. of Pulmonary, Allergy, and Critical Care Medicine, Univ. of Pittsburgh, 440 Scaife Hall, 3550 Terrace St., Pittsburgh, PA 15261 (E-mail: ameredes{at}pop.pitt.edu).

Received 7 December 1998; accepted in final form 9 June 1999.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Ameredes, B. T., W. F. Brechue, G. M. Andrew, and W. N. Stainsby. Force-velocity shifts with repetitive isometric and isotonic contractions of canine gastrocnemius in situ. J. Appl. Physiol. 73: 2105-2111, 1992[Abstract/Free Full Text].

2.   Ameredes, B. T., R. M. Rogers, M. P. Donahoe, J. F. Rosas, M. Daood, and J. Watchko. Diaphragm myosin heavy chain composition shifts in aging chronically-undernourished Fischer 344 male rats. Aging Clin. Exp. Res. 10: 112-119, 1998.

3.   Burke, R. E., D. N. Levine, P. Tsairis, and F. E. Zajac III. Physiological types and histochemical profiles in motor units of the cat gastrocnemius. J. Physiol. (Lond.) 234: 723-748, 1973[Abstract/Free Full Text].

4.   Clemmons, D. R., and L. E. Underwood. Role of insulin-like growth factors and growth hormone in reversing catabolic states. Horm. Res. 38, Suppl. 2: 37-40, 1992.

5.   Corpas, E., S. M. Harman, M. A. Pieyro, R. Roberson, and M. R. Blackman. Growth hormone (GH)-releasing hormone-(1-29) twice daily reverses the decreased GH and insulin-like growth factor-I levels in old men. J. Clin. Endocrinol. Metab. 75: 530-535, 1992[Abstract].

6.   Daughaday, W. H., and P. Rotwein. Insulin-like growth factors I and II. Peptide, messenger ribonucleic acid and gene structures, serum, and tissue concentrations. Endocr. Rev. 10: 68-91, 1989[Abstract].

7.   Donahoe, M. Nutritional support in advanced lung disease. The pulmonary cachexia syndrome. Clin. Chest Med. 18: 547-561, 1997[Medline].

8.   Everitt, A., and J. Meites. Aging and anti-aging effects of hormones. J. Gerontol. A Biol. Sci. Med. Sci. 44: B139-B147, 1989.

9.   Florini, J. R. Limitations of interpretation of age-related changes in hormone levels: illustration by effects of thyroid hormones on cardiac and skeletal muscle. J. Gerontol. A Biol. Sci. Med. Sci. 44: B107-B109, 1989.

10.   Florini, J. R., and D. Z. Ewton. Skeletal muscle fiber types and myosin ATPase activity do not change with age or growth hormone administration. J. Gerontol. A Biol. Sci. Med. Sci. 44: B110-B117, 1989.

11.   Gosselin, L. E., B. D. Johnson, and G. C. Sieck. Age-related changes in diaphragm muscle contractile properties and myosin heavy chain isoforms. Am. J. Respir. Crit. Care Med. 150: 174-178, 1994[Abstract].

12.   Gosselin, L. E., W. Z. Zhan, and G. C. Sieck. Hypothyroid-mediated changes in adult rat diaphragm muscle contractile properties and MHC isoform expression. J. Appl. Physiol. 80: 1934-1939, 1996[Abstract/Free Full Text].

13.   Hu, F., A. Comtois, and A. E. Grassino. Optimal diaphragmatic blood perfusion. J. Appl. Physiol. 72: 149-157, 1992[Abstract/Free Full Text].

14.   Izumo, S., B. Nadal-Ginard, and V. Mahdavi. All members of the MHC multi-gene family respond to thyroid hormone in a highly tissue-specific manner. Science 231: 597-600, 1986[Abstract/Free Full Text].

15.   Keiss, W., U. Kessler, S. Schmidt, and B. Funk. Growth hormone and insulin-like growth factor I: basic aspects. In: Growth Hormone and Insulin-like Growth Factor I in Human and Experimental Diabetes, edited by A. Flyvbjerg, H. Ørskov, and K. G. M. M. Alberti. New York: Wiley, 1993, chapt. 1, p. 1-21.

16.   Lanz, J. K., Jr., M. Donahoe, R. M. Rogers, and M. Ontell. Effects of growth hormone on diaphragmatic recovery from malnutrition. J. Appl. Physiol. 73: 801-805, 1992[Abstract/Free Full Text].

17.   Lewis, M. I., G. C. Sieck, M. Fournier, and M. J. Belman. Effect of nutritional deprivation of diaphragm contractility and muscle fiber size. J. Appl. Physiol. 60: 596-603, 1986[Abstract/Free Full Text].

18.   Lowry, O. H., N. J. Rosebrough, A. L. Farr, and R. J. Randall. Protein measurements with the folin phenol reagent. J. Biol. Chem. 193: 265-275, 1951[Free Full Text].

19.   McGilvery, R. W. Nutrition: fuels. In: Biochemistry, A Functional Approach (2nd ed.). Philadelphia, PA: Saunders, 1979, chapt. 40, p. 770-784.

20.   Pape, G. S., M. Friedman, L. E. Underwood, and D. R. Clemmons. The effect of growth hormone on weight gain and pulmonary function in patients with chronic obstructive pulmonary disease. Chest 99: 1495-1500, 1991[Abstract/Free Full Text].

21.   Powers, S. K., D. Criswell, R. A. Herb, H. Demirel, and S. Dodd. Age-related increases in diaphragmatic maximal shortening velocity. J. Appl. Physiol. 80: 445-451, 1996[Abstract/Free Full Text].

22.   Prezant, D. J., B. Richner, T. K. Aldrich, D. E. Valentine, E. I. Gentry, and J. Cahill. Effect of long-term undernutrition on male and female rat diaphragm contractility, fatigue, and fiber types. J. Appl. Physiol. 76: 1540-1547, 1994[Abstract/Free Full Text].

23.   Richardson, A. The relationship between aging and protein synthesis. In: Handbook of Biochemistry in Aging, edited by J. R. Florini. Boca Raton, FL: CRC, 1981, p. 70-101.

24.   Sieck, G. C. Diaphragm muscle: structural and functional organization. Clin. Chest Med. 9: 195-210, 1984.

25.   Sieck, G. C., M. I. Lewis, and C. G. Blanco. Effects of undernutrition on diaphragm fiber size, SDH activity, and fatigue resistance. J. Appl. Physiol. 66: 2196-2205, 1989[Abstract/Free Full Text].

26.   Sieck, G. C., W. Z. Zhan, Y. S. Prakash, M. J. Daood, and J. F. Watchko. SDH and actomyosin ATPase activities of different fiber types in the rat diaphragm muscle. J. Appl. Physiol. 79: 1629-1639, 1995[Abstract/Free Full Text].

27.   Thissen, J., J. Ketelslegers, and L. E. Underwood. Nutritional regulation of the insulin-like growth factors. Endocr. Rev. 15: 80-101, 1994[Abstract].

28.   Van Balkom, R. H. H., W.-Z. Zhan, Y. S. Prakash, P. N. R. Dekhuijzen, and G. C. Sieck. Corticosteroid effects on isotonic contractile properties of rat diaphragm muscle. J. Appl. Physiol. 83: 1062-1067, 1997[Abstract/Free Full Text].

29.   Vandenburgh, H. H., P. Karlisch, J. Shansky, and R. Feldstein. Insulin and IGF-I induce pronounced hypertrophy of skeletal myofibers in tissue culture. Am. J. Physiol. 260 (Cell Physiol. 29): C475-C484, 1991[Abstract/Free Full Text].

30.   Woledge, R. N., A. Curtin, and E. Homsher. Mechanics of contraction. In: Energetic Aspects of Muscle Contraction, edited by R. Woledge, N. A. Curtin, and E. Homsher. London: Academic, 1985, chapt. 2, p. 27-117.

31.   Wolf, R. F., D. B. Pearlstone, E. Newman, M. J. Heslin, A. Gonenne, M. E. Burt, and M. F. Brennan. Growth hormone and insulin reverse net whole body and skeletal muscle protein catabolism in cancer patients. Ann. Surg. 216: 280-290, 1992[Medline].

32.   Wu, F. C. Endocrine aspects of anabolic steroids. Clin. Chem. 43: 1289-1292, 1997[Abstract/Free Full Text].

33.   Yu, B. P., E. J. Masoro, and C. A. McMahan. Nutritional influences on aging of Fischer 344 rats. I. Physical, metabolic, and longevity characteristics. J. Gerontol. A Biol. Sci. Med. Sci. 40: 657-670, 1985.

J APPL PHYSIOL 87(4):1253-1259
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