Hypohydration and Acclimation: Plasma Renin Activity and Aldosterone during Heat/Exercise Stress

This study was designed to assess the effects of hydration, acclimation, and environment on the response of fluid regulatory hormones to exercise. Sixteen subjects exercised (1.34 m/sec), both pre- and post-acclimation, when euhydrated or hypohydrated (-5% of body weight) in a comfortable (20 C, rh = 40%), hot-wet (35 C, rh = 79%), or hot-dry (49 C, rh = 20%) environment. While light exercise in a thermoneutral environment had no effects on plasma levels of renin activity (PRA) or aldosterone (ALD), exercise in both hot environments resulted in significantly increased levels of these hormones. Increments in both PRA and ALD were greater when hypohydrated, and PRA effects were significantly moderated by heat acclimation in both the euhydration and hypohydration experiments. While PRA and ALD responses were generally correlated, acclimation did not consistently attenuate ALD increments. We concluded that hydration state, acclimation level, and environmental conditions all affected the responses of these hormones to light exercise. (Author)