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

¹Department of Sports Medical Sciences, Institute on Aging and Adaptation, Shinshu University Graduate School of Medicine; ²Department of Anesthesiology and Resuscitation, Shinshu University School of Medicine, Matsumoto; and ³Department 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_EXI_OS) and hypoosmotic (H_EXL_OS) conditions. In H_EXL_OS, hypoosmolality was attained by hypotonic saline infusion with DDAVP, a V₂ agonist, before exercise. P_osmol (mosmol/kgH₂O) 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_EXI_OS was higher than in C (P < 0.01), whereas that in H_EXL_OS was lower than in H_EXI_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·kgH₂O^–1) was 0.064 ± 0.012 when exercise intensity increased from C to H_EXI_OS, similar to 0.086 ± 0.020 when P_osmol decreased from H_EXI_OS to H_EXL_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_EXI_OS and H_EXL_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

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