Effects of various prostanoids on thyrotropin secretion by superfused anterior pituitary cells

Continuously superfused rat anterior pituitary cells were used to study the effects of prostaglandins (PGs) and a thromboxane (TX) on the secretion of TSH. Indomethacin, a blocker of PG synthetase, inhibited the amount of TSH secreted in response to TRH. This reduction in TRH responsiveness was overcome by administration of PGE2 in combination with the TRH. Arachidonic acid, a prostanoid precursor, increased the amount of TSH released by TRH. Superfusion with TXB2 or imadazole, an inhibitor of TX synthetase, did not change TSH secretion. PGs A2, B2, D2, F1 alpha, F2 alpha, and endoperoxide analogs U-44069 and U-46619 had no effect on hormone release. PGE1 and E2 both increased TRH-stimulated TSH, but neither compound affected basal output; PGI2 was found to stimulate TSH release. Somatostatin inhibited TRH-induced TSH, but failed to block the effects of the PGs. These studies demonstrate that PGs, but no TXs, play a role in TSH secretion. PGE1 and PGE2 appear to modulate TRH responsiveness, while PGI2 directly stimulates hormone output.