The effects of bromocriptine, thyrotropin-releasing hormone, and gonadotropin-releasing hormone on hormone secretion by gonadotropin-secreting pituitary adenomas in vivo and in vitro.

The characteristics and dynamics of hormone secretion in vivo and in vitro were investigated in six patients with gonadotropin-secreting pituitary adenomas. All six tumors secreted and contained FSH and different combinations of LH, beta-LH, and alpha-subunit. In addition, immunohistochemical examination of the pituitary tumor tissue showed staining with both LH and FSH in three and either LH or FSH in the other three tumors. TRH and GnRH stimulated hormone secretion in vivo and in vitro, and they also increased the hormone content of the cultured tumor cells. Bromocriptine significantly inhibited hormone release and reduced the hormone content of the tumor cells. In vivo, 2.5 mg bromocriptine significantly suppressed plasma hormone levels; the inhibiting effect on alpha-subunit concentrations was in general more marked than that on LH and FSH. We conclude that hormone release by gonadotropin-secreting pituitary adenomas can be stimulated by TRH and GnRH and inhibited by bromocriptine. Most of these tumors synthesize FSH, but there is a wide variation in the production of LH, beta-LH, and alpha-subunits. The sensitivity of hormone release to bromocriptine suggests that chronic therapy with this drug might have a beneficial effect on pituitary tumor size.