AJP - Endocrinology and Metabolism, Vol 240, Issue 6 700-E704, Copyright © 1981 by American Physiological Society
Resumption of prolactin secretion after dopaminergic inhibition: differential effects of dopamine and its agonists
P. D. Woolf
The recovery of prolactin (PRL) secretion following dopaminergic inhibition
was studied in vitro using pituitary monolayer cultures. PRL secretion over
4 h was inhibited comparably by 10(-6) M dopamine (DA), 10(-7) M
apomorphine (APO), and 10(-10) M bromocriptine (45%, 42%, 51%,
respectively) with reciprocal increases in intracellular hormone content.
After drug removal, the PRL secretion rate in the cultures that had been
treated with DA was 208% of the control cultures by the 2nd h but returned
to control values by 4 h, whereas the secretion rate after APO was 131-142%
of control throughout the 4-h recovery period. In contrast, PRL secretion
remained significantly less than control 20 h after the removal of
bromocriptine. Although haloperidol (10(-7) M) prevented the inhibitory
action of bromocriptine when added simultaneously, the addition of
haloperidol did not restore PRL secretion when added in the posttreatment
period. Thus, DA and APO inhibition of PRL release is readily reversible
and is followed by early PRL hypersecretion. However, bromocriptine's
effects are sustained and once started are not reversed by DA antagonists.
