The effects of growth hormone (GH) and prolactin (PRL) (1, 10, 100, 1000 or 10,000 ng/ml medium) on oxytocin, vasopressin, progesterone, cAMP and cGMP release by cultured bovine granulosa cells were studied. It was found that GH significantly stimulated oxytocin, vasopressin and cAMP but suppressed progesterone secretion. PRL tended to have the same pattern of action on nonapeptide, cAMP and steroid release, but its effect was not as great, with only a high supraphysiological dose (10,000 ng/ml) producing a statistically significant effect. No significant influence of GH on cGMP output was observed. Physiological doses of PRL (1, 10, 100 or 1000 ng/ml) significantly inhibited cGMP production whilst a high dose (10,000 ng/ml) resulted in stimulation. These observations suggested that GH may regulate ovarian oxytocin, vasopressin, progesterone and cAMP secretion. The effects of PRL on the release of these substances appeared to be non-specific, possibly resulting from its structural similarity to GH.

Keywords: Branched chain amino acid; protein; leucine; isoleucine; valine INTRODUCTION

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The secretion of oxytocin and arginine-vasopressin was demonstrated in bovine granulosa cell culture. It was found that dbcAMP or 3-isobutyl-l-methyl-xanthine (an inhibitor of intracellular cAMP metabolization) additions increased both oxytocin and vasopressin release. The Ca²⁺ ionophore A23187 also stimulated, while the Ca²⁺ channel blocker verapamil inhibited the secretion of both nonapeptide hormones. These results suggest the involvement of cAMP- and Ca²⁺-dependent intracellular mechanisms in the stimulation of both oxytocin and vasopressin secretion by bovine granulosa cells.

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