Interaction between prostaglandins and gonadotrophins in the rabbit ovary

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Abstract
1 It has been suggested that prostaglandins function as feedback modulators of hormonal actions which are mediated by adenosine 3′,5′-monophosphate (cyclic AMP). This hypothesis has been tested on the rabbit ovary, whose steroidogenic response to luteinizing hormone (LH) is mediated by the cyclic nucleotide. 2 Prostaglandin E1 (1–100 μg/ml) reduced the production of progesterone by rabbit ovaries incubated in the presence of a submaximal concentration of LH, but had no effect on the formation of this steroid when exogenous cyclic AMP was used as the stimulating agent. The prostaglandin was without effect on the formation of 20α-hydroxypregn-4-en-3-one in the presence of either LH or cyclic AMP. 3 Prostaglandin E2 (1 μg/ml) was without effect on ovarian steroidogenesis in the presence of LH. 4 There was no evidence that exogenous prostaglandin E1 was inactivated during incubation with rabbit ovaries in the presence of LH. 5 Prostaglandin E-like compounds were detected in homogenates of incubated rabbit ovaries. However, concentrations of LH sufficient to stimulate steroidogenesis did not stimulate the synthesis of these compounds by the ovary in vitro, nor their release from the ovary in vivo. 6 It is concluded that the prostaglandin-like compounds detected in the ovary are unlikely to play a role in the regulation of steroidogenesis. The results of this investigation do not support the hypothesis that prostaglandins function as general modulators of hormonal actions which are mediated by cyclic AMP.