Regulation of immunoreactive activin A secretion from cultured rat anterior pituitary cells.

Immunoreactive activin A (ir-activin A) release from cultured rat anterior pituitary cells was examined by measuring ir-activin A in culture medium by a specific radioimmunoassay. Ir-activin A release into the medium increased over 1-18 days, and reached a maximal level at 12-15 days. The basal levels of ir-activin A in the culture media were 0.70 +/- 0.10 (mean +/- SD), 1.30 +/- 0.36 and 1.83 +/- 0.44 ng/10(6) cells, when cultured for 6 days with 0, 2 and 10% fetal calf serum, respectively. LHRH induced an approximate 1.4-fold increase in ir-activin A release in contrast to a 40-60% inhibition with FSH, but LH did not affect the activin A release. In the presence of 12-o-tetradecanoylphorbol acetate (TPA), iractivin A release was enhanced, but no significant effect was induced by forskolin. Activin A was distinctly immunostained in cultured rat anterior pituitary cells. These results suggested that activin A release from the pituitary is modified by FSH and LHRH, and that the activation of protein kinase C may be involved in the action of LHRH.