The polypeptide growth factor, multiplication stimulating activity (MSA), stimulates ornithine decarboxylase (ODC) activity in isolated porcine granulosa cells maintained under chemically defined conditions in vitro. The stimulatory action of MSA is saturable, and dose-dependent (0.1-1000 ng/ml). MSA effects are additive to those of luteinizing hormone (LH), but not those of follicle stimulating hormone (FSH). Stimulation of ODC activity by MSA requires cellular protein and RNA synthesis, and appears to be mediated independently of cyclic AMP. These observations provide the first demonstration of MSA action in the mammalian ovary.
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