Effects of tri-iodothyronine, cortisol and transcriptional inhibitors on vitamin D3-enhanced thyrotrophin secretion by rat pituitary cells in vitro

Abstract

The hormone 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) has been shown to selectively enhance agonist-induced TSH release in the rat thyrotroph in vitro. The interaction of 1,25-(OH)2D3 with tri-iodothyronine (T3) and cortisol was studied in primary cultures of dispersed anterior pituitary cells. TRH (1nmol/l)-induced TSH release over 1 h was enhanced by 70% (P < 0.01) following exposure to 10 nmol 1,25-(OH)2D3/l for 24 h. Pretreatment with T3 (1 pmol/l-1 μmol/l) for 24 h caused a dose-dependent inhibition of TRH-induced TSH release. Net TRH-induced TSH release was inhibited by 85% at T3 concentrations of 3 nmol/l or greater. Co-incubation with 1,25-(OH)2D3 resulted in enhanced TRH-induced TSH r..