Acute hypoosmolality attenuates the suppression of cutaneous vasodilation with increased exercise intensity

1 Department of Sports Medical Sciences, Institute on Aging and Adaptation, Shinshu University Graduate School of Medicine; 2 Department of Anesthesiology and Resuscitation, Shinshu University School of Medicine, Matsumoto; and 3 Department of Environmental Health, Life Science and Human Technology, Nara Women’s University, Nara, Japan Submitted 7 February 2005 ; accepted in final form 18 April 2005 We examined the hypothesis that elevation of the body core temperature threshold for forearm skin vasodilation (TH FVC ) with increased exercise intensity is partially caused by concomitantly increased plasma osmolality (P osmol ). 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 ( O 2 peak ) under isoosmotic conditions (C), and at 65% O 2 peak under isoosmotic (H EX I OS ) and hypoosmotic (H EX L OS ) conditions. In H EX L OS , hypoosmolality was attained by hypotonic saline infusion with DDAVP, a V 2 agonist, before exercise. P osmol (mosmol/kgH 2 O) increased after the start of exercise in both H EX trials ( P < 0.01) but not in C. The average P osmol at 5 and 10 min in H EX I OS was higher than in C ( P < 0.01), whereas that in H EX L OS was lower than in H EX I OS ( P < 0.01). The change in TH FVC was proportional to that in P osmol in every subject for three trials. The change in TH FVC per unit change in P osmol ( TH FVC / P osmol , °C·mosmol –1 ·kgH 2 O –1 ) was 0.064 ± 0.012 when exercise intensity increased from C to H EX I OS , similar to 0.086 ± 0.020 when P osmol decreased from H EX I OS to H EX L OS ( P > 0.1). Moreover, there were no significant differences in plasma volume, heart rate, mean arterial pressure, and plasma lactate concentration around TH FVC between H EX I OS and H EX L OS ( P > 0.1). Thus the increase in TH FVC due to increased exercise intensity was at least partially explained by the concomitantly increased P osmol . esophageal temperature; threshold; plasma osmolality Address for reprint requests and other correspondence: H. Nose, Dept. of Sports Medical Sciences, Shinshu Univ. Graduate School of Medicine, 3-1-1 Asahi Matsumoto 390-8621, Japan (E-mail: nosehir{at}sch.md.shinshu-u.ac.jp )