ROLE OF PLASMA OSMOLALITY IN THE DELAYED-ONSET OF THERMAL CUTANEOUS VASODILATION DURING EXERCISE IN HUMANS

To elucidate the role of increased plasma osmolality (P-osmol), which occurs during exercise in the regulation of cutaneous vasodilation (CV D) during exercise, we determined the relationship between the change in esophageal temperature (Delta T-es) required to elicit CVD (Delta T -es threshold for CVD) and P-osmol during light and moderate exercise (30 and 55% of peak oxygen consumption, respectively) and passive body heating. Then we compared the relationship with the data obtained in our previous study [A. Takamata, K. Nagashima, H. Nose, and T. Morimot o.Am. J. Physiol. 273 (Regulatory Integrative Comp. Physiol. 42): R197 -R204, 1997], in which we determined the relationships during passive body heating following isotonic (0.9% NaCl) or hypertonic (2 or 3% NaC l) saline infusions in the same subjects. P-osmol values at 5 min afte r the onset of exercise were 287.5 +/- 0.9 mosmol/kgH(2)O during light exercise and 293.0 +/- 1.2 mosmol/kgH(2)O during moderate exercise. P -osmol just before passive body heating was 289.9 +/- 1.4 mosmol/kgH(2 )O. The Delta T-es threshold for CVD was 0.09 +/- 0.05 degrees C durin g light exercise, 0.31 +/- 0.09 degrees C during moderate exercise, an d 0.10 +/- 0.05 degrees C during passive body heating. The relationshi p between the Delta T-es threshold for CVD and P-osmol was shown to be on the same regression line both during exercise and during passive b ody heating with or without infusions [A. Takamata, K. Nagashima, H. N ose, and T. Morimoto. Am. J. Physiol. 273 (Regulatory Integrative Comp . Physiol. 42): R197-R204, 1997]. Our data suggest that the elevated b ody core temperature threshold for CVD during exercise could be the re sult of increased P-osmol induced by exercise and is not due to reduce d plasma volume or the intensity of the exercise itself.