ANGIOTENSIN-II INTERFERES WITH STEROIDOGENESIS IN PORCINE GRANULOSA-CELLS

The elements for the synthesis and activity of the vasopressor angiote nsin II (All) are present in the mammalian ovary. In the present inves tigation, the effects of All were determined on three parameters of st eroidogenic function in porcine granulosa cells in vitro: the accumula tion of progesterone, the cellular content of the enzyme 3 beta-hydrox ysteroid dehydrogenase Delta(5-4) isomerase (3 beta-HSD), and the accu mulation of mRNA for 3 beta-HSD. Cells were incubated with LH (200 ng/ ml) in the presence or absence of All (10(-7) M) or phorbol 12-myrista te 13-acetate (PMA, 10(-7) M); doses of All from 10(-10) to 10(-6) M i n the presence or absence of LH; the All receptor antagonist saralasin (10(-6) M) in the presence of All or in combination of All and LH; an d All in the presence or absence of (Bu)(2) cAMP. The results demonstr ate that LH increased progesterone, 3 beta-HSD message, and 3 beta-HSD content. Both PMA and All interfered with the LH-induced progesterone accumulation, reducing the response by 50% or more. All also abrogate d the LH-induced increases in 3 beta-HSD mRNA and 3 beta-HSD enzyme co ntent in porcine granulosa cells. The All inhibition was dose-dependen t. The All receptor antagonist saralasin blocked the inhibitory effect s of All on LH-induced steroidogenic events. All interfered with the ( Bu)(2) cAMP induction of steroidogenesis and 3 beta-HSD mRNA and enzym e accumulation when (Bu)(2) cAMP was present at a concentration of 30 mu M. Pretreatment of cell cultures with PMA for 24 h to downregulate protein kinase C (PKC) reduced basal and LH-stimulated progesterone as well as 3 beta-HSD and mRNA accumulation. Comparison across the PMA d own-regulated cultures demonstrated that LH mildly stimulated progeste rone accumulation, but increased SP-HSD mRNA accumulation 4-fold relat ive to the PMA down-regulated control. All had no effect on LH-stimula ted 3 beta-HSD mRNA accumulation, further suggesting that Ail acts thr ough the PKC pathway. The results indicate that the mechanism by which All inhibits steroidogenesis includes inhibition of the transcription of the 3 beta-HSD gene or alteration of 3 beta-HSD mRNA stability. Al l functions through its receptor to express this inhibition, which inc ludes some interference with cellular function beyond the generation o f cAMP, All may be a paracrine agent associated with the limitation of follicular development in the pig ovary.