Vasoactive intestinal peptide induces the synthesis of the cholesterol side-chain cleavage enzyme complex in cultured rat ovarian granulosa cells.

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Abstract
Vasoactive intestinal peptide (VIP) has been identified in ovarian nerves and stimulates steroid secretion from immature ovaries. To gain insight into its mechanism of action, the effect of VIP on the synthesis of the cholesterol side-chain cleavage enzyme complex was studied in ovarian granulosa cells from immature estrogen-primed rats. The cells were cultured for 48 hr in serum-free medium; the proteins were labeled with [35S]methionine; and the synthesis of cytochrome P-450, iron-sulfur protein, and NADPH:iron-sulfur protein reductase was evaluated by electrophoretic analysis after immunoisolation with polyclonal antibodies directed against the bovine adrenal enzymes. VIP at concentrations ranging from 0.001 to 1 .mu.M stimulated 3-to 5-fold the synthesis of cytochrome P-450 and iron-sulfur protein. Peptide NH2-terminal histidine, COOH-terminal isoleucine, which has >50% sequence homology of VIP, stimulated the synthesis of both proteins at .apprxeq.50% of VIP effectiveness. Secretin, another member of the glucagon-secretin family of peptides, which has only 30% sequence homology of VIP, was without effect. Similar results were observed with the NADPH:iron-sulfur protein reductase. VIP-induced synthesis of the cholesterol side-chain cleavage enzyme complex was accompanied by a dose-related increase in cAMP accumulation and progestin formation. It is concluded that VIP regulates the synthesis of the ovarian cholesterol side-chain cleavage enzyme complex, which catalyzes the rate-limiting reaction in progesterone biosynthesis, and that the VIP effect is at least partially mediated through cAMP. It is suggested that a stimulatory action of VIP on the synthesis of ovarian progesterone may contribute to regulating the functional development of the ovary.