Response of plasma prolactin to changes in ambient temperature and humidity in man.

The present study examined the relationship between plasma PRL and ambient temperature and relative humidity (RH) in man. Six normal men sat in an environmental room on four occasions. On each occasion, a thermoneutral control period at 27 C dry bulb (db)/16 C wer bulb (wb; 32% RH) was followed by a 90-min exposure to 27 C db/16 C wb, 13 C db/9 C wb, 45 C db/26 C wb, or 27 C db/26 C wb (92% RH) and a recovery period. Blood was drawn at 30-min intervals. Plasma PRL rose 53% (P < 0.05) in the heat and fell 37% (P < 0.05) in the cold in comparisons with control levels. No changes occurred during increased RH alone. Maximum PRL changes were associated with an increase in mean skin temperature of 3.0 C in the heat and a decrease of 4.3 C in the cold. Corresponding changes in auditory meatal temperature were +1.0 and -0.2 C, respectively. Plasma osmolality and serum Na+ and K+ levels did not change, except in the cold where serum K+ rose 0.6 meq/liter (P < 0.01). These data suggest an association between ambient temperature and plasma PRL in man which is not associated with changes in water and electrolyte status.