Effect of 1,25(OH)2D3 on the TSH secretion from rat pituitary cells.

1,25(OH)2D3 slightly increases basal TSH in the incubation media after a 24 h incubation with increasing amounts of the hormone. The TRH induced TSH response increased significantly in the presence of 10(-8)M 1,25(OH)2D3 (P less than 0.05). The intracellular concentration of TSH after the TRH test showed a slight decreasing tendency after a 24 h incubation with increasing amounts of 1,25(OH)2D3. The presence of verapamil (10(-8) M) and propranolol (10(-8) M) blunted the enhancing effect of 1,25(OH)2D3. The results indicate an effect of 1,25(OH)2D3 on the secretion of TSH.