Multiple actions of recombinant activin-A in vivo.

Activin stimulates the secretion of FSH from cultured pituitary cells and enhances the differentiation of erythroid progenitors in vitro. The role of activin in the physiological regulation of either process, however, is unknown. We report here that systemic administration of recombinant human activin-A to immature female rats caused a marked increase in serum FSH levels. In addition, in ovariectomized estrogen-treated rats recombinant human activin-A induced a small but statistically significant increase in the circulating concentrations of red blood cells and hemoglobin. These data demonstrate the efficacy of activin in vivo, supporting the hypothesis that this protein is an important regulator of gonadotropic and erythroid function.