Sex-related responses of beta-endorphin, ACTH, GH and PRL to cold exposure in humans

To establish a possible different reaction between the male and the female to short-term exposure to cold, thermal, cardiovascular and pituitary hormonal responses to cold stress were measured in eight normal men and eight women (ages 19–24). The women were eumenorrheic and were tested in the follicular phase. Each subject, lightly clad, was required to remain for 30 min in a room at an ambient temperature of 2 5°C followed by a 30 min period in a cold room at 4°C. A month later, control tests were carried out at a constant 25°C temperature for 1 h in the same subjects. Skin temperature, heart rate, blood pressure and plasma levels of beta-endorphin, ACTH, cortisol, GH and PRL were measured before and after cold exposure in the two groups. Before the test, all examined parameters were similar in the two groups. During cooling, blood pressure rose and pulse rate decreased significantly in the men, but not in the women, whereas skin temperature dropped in both groups. However, after cold exposure skin temperature was significantly lower in the women than in the men. A slight, but not significant increase in beta-endorphin, ACTH, cortisol and GH levels was observed after cooling in the men, whereas the women showed significant increments of these hormones, When values of skin temperature were combined with the differential (after minus before cold test) hormonal values, significant negative correlations were found for beta-endorphin, ACTH, cortisol and GH. As observed by other authors, a significant and peculiar cold-induced decline in plasma PRL levels was observed in the men; by contrast, a slight, but not significant decrement of PRL was found in the women. Control tests at a constant 25°C temperature did not show significant thermal, cardiovascular or hormonal changes in any subject. These data reflect stronger thermal, cardiovascular and PRL responses to cooling in men than in women. On the other hand, the women, but not the men, showed significant cold-stress-induced increments of beta-endorphin, ACTH and GH, suggesting that the more efficient adaptation to cold of the men might be what prevents the stress-induced hormonal changes observed in the women.