Lowering prolactin level in a hyperprolactinemic man: responses of luteinizing hormone, follicle-stimulating hormone, and testosterone.

A 25-year-old man with hypogonadotropic hypogonadism and elevated prolactin levels, presumably from a microadenoma of the pituitary gland, was treated with bromocriptine mesylate. After three weeks, the prolactin level had fallen and the gonadotropin levels had shown a substantial rise, reaching supraphysiologic levels by eight weeks, eventually returning to normal by 15 weeks. The serum testosterone level did not rise until after three weeks and reached a maximum by 15 weeks. When the bromocriptine therapy was stopped for one week, all indexes returned to near pretreatment levels. Within two weeks of re-treatment with bromocriptine, the prolactin level had fallen and both testosterone and gonadotropin levels rose. These findings suggest that prolactin may block the secretion of luteinizing-releasing hormone, or may prevent the pituitary gland from responding to it.