ALDOSTERONE AND VASOPRESSIN RESPONSES IN THE HEAT - HYDRATION LEVEL AND EXERCISE INTENSITY EFFECTS

We examined the separate and combined effects of hypohydration level a nd exercise intensity on aldosterone (ALD) and arginine vasopressin (A VP) responses during exercise-heat stress. Nine heat acclimated men pe rformed 50 min of treadmill exercise in a warm room (30 degrees C dry bulb (DB), 50% relative humidity (RH) at 25%, 45% and 65% VO2max when euhydrated and when hypohydrated by 3% and 5% of body weight. Blood sa mples were drawn at rest and at 20 min of exercise. ALD and AVP increa sed (P < 0.05) in a graded manner with hypohydration level, and this e ffect persisted during exercise-heat stress. High intensity exercise p roduced greater ALD and AVP increases than low intensity exercise. ALD responses during exercise were independent of hypohydration level. AV P responses were closely related to osmolality (N = 6 of 7 subjects; r = 0.51 to r = 0.98; average r = 0.84) despite varying hydration, exer cise intensity, or core temperature. We conclude that: 1) ALD and AVP increase in a graded manner with hypohydration, and this effect persis ts during exercise-heat stress; 2) ALD and AVP increases elicited by e xercise are greater during high intensity than low intensity exercise; 3) Hypohydration and exercise intensity have additive effects on ALD; and 4) AVP responses are closely coupled to osmolality.