Effects of cross-gender steroid hormone treatment on prolactin concentrations in humans

It is well known that peripheral prolactin levels are significantly higher in menarcheal women than in men. Higher levels of prolactin in menarcheal women are related to exposure to higher levels of estrogen in women than in men. Increased exposure to androgens in men has also been proposed as a possible reason to account for lower prolactin levels in men; however, this suggestion has not been conclusively proven. The current study sought to evaluate the cross-gender effects of male and female hormones on basal levels and the pituitary store of prolactin in humans. Four groups of individuals were involved: normal men and women, male and female transsexuals primed with female hormones and testosterone, respectively for at least 6 months. A metoclopramide challenge test was carried out on each subject of each group. Subjects were rested for 1 h, with an indwelling catheter in the antecubital vein, before a blood sample was collected for estimation of basal hormone levels. Following an oral ingestion of 10 mg of metoclopramide, blood samples were collected at 15, 30, 60, 90, 120, 150 and 180 min. Prolactin, estradiol and testosterone concentrations were measured by radioimmunoassay. Basal levels as well as metoclopramide-induced releases of prolactin (as measured by area under the curve) in normal women were significantly higher (p less than 0.05) than corresponding levels in normal men. Following long-term priming with female hormones, the pattern of response to metoclopramide in male transsexuals was dramatically changed.(ABSTRACT TRUNCATED AT 250 WORDS)