Hypothalamic-pituitary-testicular function in men with PRL-secreting tumors

We studied the hypothalamic-pituitary-gonadal system in 33 men with PRL-secreting tumors to determine at which level(s) high PRL levels interfere with testicular function. In basal conditions serum PRL levels ranged between 24-4500 ng/ml, serum LH and FSH concentrations were lower than normal in 61% and 39% of patients; low testosterone (T) levels and sexual impotence appeared more common (85% and 88%) than that we expected on the basis of gonadotropin deficiency. Mean T increase after hCG in 14 patients with prolactinomas was significantly less than in normals (3.3 +/- 0.7) ng/Ml vs 7.3 +/- 0.5 ng/ml; p less than 0.025); a significantly higher T response to hCG was obtained in 5 cases retested after PRL levels had been reduced by therapy. GnRH test induced a normal LH rise in 45% of patients, Mean serum LH increase after clomiphene administration did not differ from that in normals, though 4 out of 10 patients showed an impared response. Metoclopramide injection did not cause a rise of LH in 11 patients so tested. These data, while not excluding a central influence of PRL on LHRH, suggest that in men the antigonadotropic effects of PRL are mainly exerted at the gonadal levels.