Stimulation of prolactin release in vivo by thyrotropin-releasing hormone (TRH) through direct action on the ectopic rat pituitary.

Abstract

Hypophysectomized female rats which had received renal grafts of anterior pituitary (AP) were sampled by heart puncture under pentobarbital (PB) anesthesia. Serum prolactin in sequential samples from each rat was measured by radioim-munoassay to determine the effect of exogenous TRH and median eminence (ME) lesions on prolac-tin release fromectopic AP. A pretreatment sample was taken from each rat 45 min after PB injection after which either TRH (0.3–0.6 µig) or isotonic saline was injected iv, and samples were taken at 10 and 30 min post-treatment. TRH caused a significantly greater increase in prolactin at 10 min than did saline. Serum prolactin at 30 min post-treatment always tended to be higher after TRH than after saline, but this difference was not statistically significant in allexperiments. I order to determine whether the effect of TRH might be mediated by the hypothalamus, the experiments were repeated in rats in which ME lesions had been placed 7 days previously. Compared with rats subjected to...