| Abstract: | Pretreatment of normal subjects with apomorphine, a dopamine receptor agonist, resulted in significant impairment of the subsequent prolactin (PRL) response to thyrotropin releasing hormone (TRH). The mean maximal increment of PRL was 27.9+/-2.4 ng/ml after TRH alone, and 11.9+/-3.0 ng/ml (P less than 0.001) after apomorphine plus TRH. In contrast, the.thyrotropin (TSH) response to TRH was unaffected by apomorphine (10.5+/-2.9 vs. 9.5+/-1.8 muU/ml, P greater than 0.5). These results demonstrate that dopaminergic effects are capable of inhibiting PRL responses to TRH, probably via a direct effect on the lactotrope cell. They also suggest that dopaminergic influences are not important in the regulation of TSH secretion. |
