Dopamine inhibition of prolactin release but not synthesis in the male Syrian hamster: in vitro studies.

The hypothalamic mechanisms controlling prolactin (PRL) cell function in the male Syrian hamster are unclear. Equally unclear is the role of dopamine (DA) in regulating lactotrophic cell activity in long photoperiod-exposed hamsters particularly with respect to PRL synthesis and release. The synthesis of PRL, as measured by the incorporation of 3H-leucine into newly synthesized PRL, by anterior pituitary glands from male hamsters is linear over a five h incubation period. Approximately two-fold more 3H-PRL remained in the pituitary glands than in the medium by the end of the incubation period. The incubation of hamster hemipituitaries with DA at concentrations of either 5 X 10(-7) M or 5 X 10(-5) M, resulted in a 77% to 83% inhibition of the release of immunoreactive PRL into the medium as compared with controls. Similarly, the release of 3H-PRL into the medium was inhibited by 71% to 76% as compared with controls; however, the synthesis of PRL was virtually the same among the experimental and control groups. These results suggest that DA may be an important regulator of short-term PRL release but not synthesis in the long photoperiod-exposed male hamster.