Hormonal and Hemodynamic Effects of Heat and Cold Tolerance Tests Before and After Multiple Cold Air Exposures

摘要

Ten male volunteers were repeatedly exposed, semi-nude, to cold (4 C) air for 30 minutes. Prior to and following the repeated cold air exposures, each subject was given a heat tolerance test (HTT) and a cold tolerance test (CTT), consisting of a 30 minute exposure to 48 C or 5 C air, respectively. Acute effects of the thermal tolerance tests had the following endocrinological effects: Plasma norepinephrine (NE) levels rose 175%, associated with vasco-construction and a rise in mean arterial pressure (MAP), during this relatively mild CTT. Plasma epinephrine (E) levels rose significantly during the HTT but not during the CTT. Plasma Renin Activity (PRA) was elevated in the heat but not in the cold, suggesting that Angiotensin II does not contribute to the general pressor effects associated with cold pressure. When compared before and after the repeated cold exposures, the physiological and biochemical changes that occurred during thermal tolerance tests showed the following differences: Finger skin temperatures were significantly lower during the final CTT. This drop in peripheral skin temperatures may be indicative of 'insulative' cold adaptation. The NE response to a HTT increased significantly following the repeated cold exposure. During or following the second HTT, MAP and plasma levels of E, prolactin, cortisol, and aldosterone also differed from the levels found during the first HTT. These findings tend to confirm the hypothesis that repeated cold exposures can alter responses to a standardized heat exposure and that adaptation to cold may decrease man's ability to tolerate heat. (aw)