Thyrotropin-releasing hormone blockade of the ergocryptine and apomorphine inhibition of prolactin release in vitro.

The interaction of thyrotropin-releasing hormone (TRH) and ergocryptine or apomorphine in affecting prolactin secretion was examined. Ergocryptine and apomorphine inhibited the release of 3H-prolactin labeled in an in vitro incubation of the rat anterior pituitary and led to a retention within the gland of 3H-prolactin. TRH (1.4 X 10(-8) M) partially blocked the inhibitory effect of 4 x 10(10) M ergocryptine on 3H-prolactin release and totally blocked the effect on radioimmunoassayable prolactin release. TRH also completely blocked the inhibitory effects of 5 x 10(-8) M apomorphine on both 3H-prolactin and radioimmunoassayable prolactin release. Since TRH can also completely block the inhibitory effects of dopamine upon prolactin secretion, these results are consistent with apomorphine and ergocryptine stimulating "dopaminergic" sites and also further support the role of TRH as a prolactin-releasing factor.