The responses of 22 kD immunoreactive growth hormone and its relationships with changes of body water and sweating characteristics during heat acclimation

Date of Completion

January 2005


Biology, Animal Physiology|Health Sciences, Recreation




This study examined responses of 22 kD immunoreactive growth hormone (iGH), body fluid regulation, and sweating characteristics during heat acclimation (HA). HA was achieved via exercise in the heat (37°C, 52% rh) for 90 min or until volitional exhaustion during 8 consecutive days. Eight men exhibited mean (SD) age, height, weight, body fat, and V˙O2max of 22 (3) y, 176 (8) cm, 78.56 (12.00) kg, 10 (3) %, and 50.55 (4.29) (ml·kg-1·min-1), respectively. Morning iGH concentration significantly decreased by 48% over the first 3 days, while serum aldosterone significantly increased by 143%. Extracellular fluid volume was significantly increased by 0.7 L (4%) by HA. Sodium balance was similar across days, although morning urine sodium concentration decreased. Sweat rate was significantly elevated on day 8 by 0.5 L·h-1 compared to day 1. Sweat sodium concentration significantly decreased from 28 (6) mEq·L-1 on day 2 to 18 (4) and 19 (4) mEq·L -1 on days 4 and 8, respectively. ONSET was significantly reduced by 0.3°C by HA. iGH and aldosterone significantly increased during exercise-heat exposure, however, the responses of both hormones were similar across HA days. ^ 22 kD iGH does not appear to be involved in fluid retention during HA. The observation that resting levels were suppressed indicates that HA may alter the hypothalamic control or pituitary secretion of 22 kD iGH, however, the physiological consequences of this were not apparent. iGH was not related to ONSET, sweat sodium, sweat rate, or aldosterone, further, iGH measured during exercise was not altered by HA. ^