In vivo release of prolactin in Rana ridibunda following an intravenous injection of thyrotropin-releasing hormone.

All experiments were performed on female Rana ridibunda during the months of April and May. Injections were made into the canulated vena abdominalis and blood samples were taken up to 8 hr thereafter and checked for prolactin concentration using a heterologous frog radioimmunoassay. An injection of 10 micrograms TRH (thyrotropin releasing hormone; pGlu-His-Pro NH2) will elevate control serum levels of 28.54 +/- 5.40 ng/ml prolactin to 59.56 +/- 8.78 ng/ml (n = 6) and this within half an hour. A smaller increase was present with 1 microgram of TRH and none with 0.1 or 0.01 microgram. Prolactin remains elevated up to 2 hr after the injection but reaches control values again after 4 hr. Two days after removal of the pars distalis serum levels have declined to 14.48 +/- 1.67 ng/ml (n = 15) and no influence of TRH injections, tested at several doses, on this is seen. previous thyroxine (T4) and tri-iodothyronine (T3) assays using the same blood have revealed that 1 and 10 micrograms TRH also increases T4 in a dose-related way after 1 hr, with a maximal increase at 2 hr, and T3 after 4 hr. It is concluded that TRH is able to induce the release of both prolactin and TSH from the hypophysis in the frog R. ridibunda as it does in mammals.