Prolonged treatment with
bromocriptine may lead to a decrease in
tumor size in patients with a gonadotroph, alpha-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 alpha-subunit concentrations in 10 such
adenomas in vitro. The release of FSH,
LH, alpha-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 alpha-subunit release which increased with duration of culture. Withdrawal of
bromocriptine during the culture period led to a recovery of
gonadotropin or alpha-subunit release in the 2
tumors in which it was tested. Intracellular
hormone and alpha-subunit concentrations in 3 of 4
tumors cultured for 4 or more weeks were significantly lower in
bromocriptine-treated than in untreated cells. We conclude that 1)
bromocriptine can suppress the in vitro release of
gonadotropins and alpha-subunit from the majority of clinically nonfunctioning, gonadotroph, and alpha-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 alpha-subunit, which eventually may lead to decreased intracellular concentrations of these
glycoproteins.