Interactions among epinephrine, thyrotropin (TSH)-releasing hormone, dopamine, and somatostatin in the control of TSH secretion in vitro.

Epinephrine and TRH independently release TSH from rat anterior pituitary cells in primary monolayer culture (ED50, 11 and 5 nM, respectively; maximum responses, 80% and 110%, respectively). The effects of these compounds together are additive, even at concentrations at which each is maximally effective alone. Dopamine inhibited basal and epinephrine-stimulated TSH secretion by 25 +/- 5% (+/-SE; ED50, 50 +/- 9 nM in each case). Somatostatin was effective against epinephrine-stimulated, but not basal, TSH secretion (80 +/- 4% inhibition; ED50, 1 +/- 3 nM). The data show that epinephrine is a potential regulator of TSH secretion by its own action and via its interactions with TRH, dopamine, and somatostatin.