Submitted on February 7, 2005
Accepted on April 18, 2005
ACUTE HYPOOSMOLALITY ATTENUATES THE SUPPRESSION OF CUTANEOUS VASODILATION WITH INCREASED EXERCISE INTENSITY
Hiroyuki Mitono1, Hiroshi Endoh2, Kazunobu Okazaki2, Takashi Ichinose2, Shizue Masuki2, Akira Takamata3, and Hiroshi Nose2*
1 Department of Anesthesiology and Resuscitation, Shinshu University School of Medicine, Matumoto, Nagano, Japan
2 Department of Sports Medical Sciences, Institute on Aging and Adaptation, Shinshu University Graduate School of Medicine, Matumoto, Nagano, Japan
3 Department of Environmental Health, Life Science and Human Technology, Nara Women's University, Nara, Nara, Japan
* To whom correspondence should be addressed. E-mail: nosehir{at}sch.md.shinshu-u.ac.jp.
We examined the hypothesis that elevation of the body core-temperature threshold for forearm skin vasodilation (THFVC) with increased exercise intensity is partially caused by concomitantly increased plasma osmolality (Posmol). Eight young male subjects, wearing a body suit perfused with warm water to maintain the mean skin temperature at 34 ± 1 °C (ranges), performed 20-min cycle-ergometer exercise at 30% peak aerobic power (VO2peak) under isoosmotic condition (C), and at 65% VO2peak under isoosmotic (HEXIOS) and hypoosmotic (HEXLOS) conditions. In HEXLOS, hypoosmolality was attained by hypotonic saline infusion with DDAVP, a V2 agonist, before exercise. In C and HEXIOS, isotonic saline was infused before exercise to adjust the plasma volume (PV) at 5-10 min of exercise, around which time THFVC was observed, to the same level as in HEXLOS. Posmol (mosmol.kgH2O-1) increased after the start of exercise in both HEX trials (P < 0.01) but not in C. The average Posmol at 5 and 10 min was 301 ± 1 in HEXIOS, higher than 293 ± 1 in C (P < 0.01), while that in HEXLOS was 298 ± 1, lower than in HEXIOS (P < 0.01). The change in THFVC was proportional to that in Posmol; 37.44 ± 0.09 °C in HEXIOS, higher than 36.98 ± 0.07 °C in C (P < 0.01), and 37.21 ± 0.08 °C in HEXLOS, lower than in HEXIOS (P < 0.01). The change in THFVC per unit change in Posmol (
THFVC/Posmol, °C mosmol-1.kgH2O) was 0.064 ± 0.012 when exercise intensity increased from C to HEXIOS, similar to 0.086 ± 0.020 when Posmol decreased from HEXIOS to HEXLOS (P > 0.1). Moreover, there were no significant differences in PV, heart rate, mean arterial pressure, and plasma lactate concentration around THFVC between HEXIOS and HEXLOS (P > 0.1). Thus, the increase in THFVC due to increased exercise intensity was at least partially explained by the concomitantly increased Posmol.
