Effect of age and sex on circulating and pituitary prolactin levels in human.

In an attempt to determine whether age or sex affects prolactin secretion in the human, basal levels of serum prolactin, and its response to TRH administration as well as the pituitary content of this hormone were compared between both sexes and among the different agent groups. In 315 adult subjects of various ages, the mean basal levels of prolactin were found to be higher in women than in men of the same age groups with the exception of the sixth decade. The effect of age on serum prolactin concentrations, on the other hand, was not demonstrated. Similarly, the prolactin response to intravenous injections of 500 mug of TRH was significantly greater in female subjects than in males of both young and aged groups. No relationship between the prolactin response and the day of menstrual cycle in young women was apparent. Although quantitative difference in TRH-induced prolactin release was not observed between young and elderly subjects, the occurrence of prolactin peak and the elimination of the circulating prolactin following TRH administration were delayed in the aged groups. Taken together with the demonstration of a higher content of this hormone in female pituitary glands compared with those of males, it was concluded that prolactin secretion is enhanced in female subjects throughout life after puberty and that aging, per se, is not associated with an alteration in the rate of secretion of this hormone in human subjects.