In vitro Studies with Thyrotropin Releasing Factor. ∗

Summary

Porcine TRF stimulates the release of TSH from rat anterior pituitaries in vitro at doses as small as 0.01 nanog. By increasing the doses of TRF, greater amounts of TSH are released into the incubation media. The pituitary response to TRF is inhibited by small amounts of T₃ and T₄. Act D does not abolish the response to TRF, indicating that de novo synthesis of TSH is not required for TRF to exert its effect, _a- and β-MSH do not stimulate the release of TSH in vitro and did not reverse the inhibitory effect of T₄ on TSH release in vitro. Preincubation with Act D reverses the inhibition of TSH release induced by T₃ and T₄. This may indicate that Act D interferes with the formation of inhibitory substances, induced by T₃ and T_4, which suppress the release of TSH after TRF.