Effects of thyroliberin, triiodothyronine and cyclic guanosine 3'5'-monophosphate on the volume of nuclei of thyrotropic cells in rat anterior pituitary in vitro.

Influence of TRH, T3 and cGMP on the volume of thyrotropic cells nuclei in rat pituitary in vitro has been examined. A significant increase of the volume of thyrotropic cells nuclei in the culture exposed to TRH, in another one exposed to cGMP and in the third one exposed to both TRH and cGMP together have been observed. The mean volume of cells nuclei within the group exposed to T3 was significantly lower, when compared to the control. T3 inhibited the TRH-induced increase of the volume of thyrotrophs nuclei. The obtained results suggest that the role of cGMP and T3 in the regulation of the thyrotropic cell function are independent and rather opposed. Since TRH increases the level of cAMP in the anterior pituitary, additive effect of TRH and exogenous cGMP support the assumption that both the cyclic nucleotides within the thyrotropic cell act in the same direction.