Bromocriptine Increasingly Suppresses the in Vitro Gonadotropin and α-Subunit Release from Pituitary Adenomas during Long Term Culture

Prolonged treatment with bromocriptine may lead to a decrease in tumor size in patients with a gonadotroph, α-subunit-secreting, or clinically nonfunctioning pituitary adenoma. The effectiveness of the treatment, however, may depend on its duration. We investigated the effects of prolonged incubation with bromocriptine on the release and intracellular hormone and asubunit concentrations in 10 such adenomas in vitro. The release of FSH, LH, α-subunit, or a combination of these was demonstrated in 7 tumors. Bromocriptine significantly suppressed this release in 6 tumors. In 5 tumors bromocriptine had an inhibitory effect on gonadotropin and/or α-subunit release which increased with duration of culture. Withdrawal of bromocriptine during the culture period led to a recovery of gonadotropin or α-subunit release in the 2 tumors in which it was tested. Intracellular hormone and a-subunit concentrations in 3 of 4 tumors cultured for 4 or more weeks were significantly lower in bromocriptinetreated than in untreated cells. We conclude that 1) bromocriptine can suppress the in vitro release of gonadotropins and α-subunit from the majority of clinically nonfunctioning, gonadotroph, and a-subunit-secreting pituitary adenomas; 2) during prolonged incubation of these tumors with bromocriptine, this drug has a time-dependent increasing inhibitory effect on the release and synthesis of gonadotropins and a-subunit, which eventually may lead to decreased intracellular concentrations of these glycoproteins.