Effects of activin A on anterior pituitary cells fractionated by centrifugal elutriation

Abstract

We have shown previously that activin A increases the number of immunoreactive follicle-stimulating hormone (FSH) cells. To further investigate the action of activin A, we examined its effects on anterior pituitary cells fractionated by centrifugal elutriation. Before activin A treatment, FSH cells were widely distributed among various fractions; a higher proportion of FSH cells was found in larger cell fractions (fractions 5–9), and a lower proportion in smaller cell fractions (fractions 2–4). After culture of the cells in each fraction with activin A (10 ng/ml) for 72 h, the number of FSH cells in fraction 4 only was significantly ( P< 0.05) higher by 225% than that in cells cultured without activin A. The amount of FSH secreted into the medium was minimal or undetectable in fractions 1–4. However, FSH secretion tended to be, or was significantly ( P <0.0 l in fraction 9), stimulated by activin A in fractions 5–9, in which the numbers of FSH cells were not significantly affected. These results suggest a dual mode of action of activin A on FSH: activin A increases the number of FSH cells in a specific type(s) of middle-sized cell fraction, and stimulates FSH secretion at least from larger cells without affecting the number of FSH cells.