title: Bihormonal regulation of the thyrotropin-releasing hormone receptor in mouse pituitary thyrotropic tumor cells in culture.
abstract: Receptors for thyrotropin-releasing hormone (TRH) are present on mouse pituitary thyrotropic tumor cells. Incubation of thyrotropes with 100 nM TRH or 4 nM L-triiodothyronine (T3) for 48 h decreased the number of TRH receptors to approximately equal to 50 and 20% of control, respectively. There was no effect on the equilibrium dissociation constant which was 3-5 nM. The depletion in the number of available TRH receptors was time- and dose-dependent. TRH, 100 nM, decreased the receptor number to 70% after 24 h, 50% after 48 h, and 45% of control after 72 h. T3, 4 nM, decreased the receptor number to 52% after 24 h, 20% after 48 h, and 17% of control after 72 h. After 48 h, half-maximal depletion occurred with 1-2 nM TRH and approximately equal to 0.15 nM T3. Incubation with 100 nM TRH and 4 nM T3 caused a significantly greater reduction in the receptor level than either hormone alone. The decrease in the receptor level was reversible within 72 h after removal of TRH, 100 nM, but was only partially reversed, from 20 to 40% of control, after removal of T3, 4 nM, after 120 h. By regulating the number of available TRH receptors on the thyrotrope. TRH and T3 interact to control thyrotropin release.
mesh_terms: D002478:Cells, Cultured; D009374:Neoplasms, Experimental / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000187:drug effects* / Q000378:metabolism; D013972:Thyrotropin / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism* / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D011956:Receptors, Cell Surface; D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin