Studies on the action of activin A

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1) Studies in Pituitary Cells: We studied the effect of activin A in human GH-producing pituitary adenoma cells in primary culture. Activin A stimulated FSH secretion in these cells and increased cytoplasmic free calcium concentration by augmenting calcium entry. 2) Studies in Fibroblasts: In Balb/c 3T3 cells, activin A inhibited cell-cycle progression induced by insulin-like growth factor-I (IGF-I). Activin did not affect calcium entry induced by IGF-I but significantly reduced IGF-mediated production of diacylgylcerol, which may be causally related to its action on cell-cycle progression. 3) Studies in Pancreatic Islet: In pancreatic islets, immunoreactivity of activin A existed in both A- and D-cells. Electron Microscopic analysis revealed that activin A and glucagon existed in the same secretory graniles in A-cells. Given that activin is a potent stimulant of insulin secretion, it is possible that activin A acts as a paracrine regulator of insulin secretion. 4) Studies in Hepatocytes: In cultured hepatocytes, activin A blocked DNA synthesis induced by EGF. Activin inhibited DNA synthesis by acting on it sown receptors. Hepatocytes produce significant amount of activin A when the growth is stimulated. Stimulatory action of EGF was enhanced when follistatin was included in culture medium, suggesting that endogenous activin A attenuates DNA synthesis induced by EGF.