MELATONIN AND NOREPINEPHRINE RESPONSES TO COLD-EXPOSURE IN HUMANS

Contrasting data have been reported in the different experimental condition about melatonin response to stress and particularly to cold exposure. Our previous findings evidenced sex related responses of ACTH and Beta-Endorphin to low temperature. Aim of this study was to evaluate serum Melatonin and Norepinephrine levels in humans after short time cold exposure (30 min-4-degrees), taking into account possible differences between sexes. The test consisted in the individual permanence of short dressed healthy subjects (10 males and 10 females -age: 19-26), in a room at ambient temperature of 25-degrees-C for 30 min. followed by a period of 30 min. in a cold room at 4-degrees-C. A month later control tests at constant 25-degrees-C temperature for one hour were performed in the same subjects. During cooling, blood pressure rose and pulse rate decreased significantly in men, but not in women, whereas skin temperature dropped in both groups. However, after cold exposure skin temperature was significantly lower in women than in men. Female subjects showed a significant increase in melatonin concentration after cold stress (p < 0,001); male subjects didn't show any significant change in melatonin levels after cooling. All the subjects showed a significant cold-induced increase in norepinephrine levels with a significantly higher response (p <0,05) in men than in women. The present findings suggest sex-related melatonin involvement in human adaptation to low temperature and support the hypotesis that pineal gland may be influenced not only by sympathetic activation but also by other projection including endogenous opioid system.