T3 enhancement ofin vitro estradiol-17β secretion by oocytes of rainbow trout,Salmo gairdneri, is dependent on cAMP.

The cellular mechanism of action of 3,5,3'-triiodo-L-thyronine (T3) in enhancing SG-G100 gonadotropin-induced ovarian secretion of 17β-estradiol (E2) was studiedin vitro using oocyte follicular preparations of rainbow trout. The dependence of the T3 stimulatory action on the level of intracellular 3',5'-cyclic adenosine monophosphate (cAMP) was shown in experiments in which forskolin or dibutyryl cAMP enhanced E2 secretion. In the presence of partially purified salmon gonadotropin (SG-G100), T3 stimulation of E2 secretion was prevented by theophylline, suggesting that T3 may exert part of its stimulatory action by inhibiting phosphodiesterase.