A stimulatory effect of somatostatin: enhancement of activin A-mediated FSH secretion in rat pituitary cells.

The interaction between somatostatin and activin A was studied in terms of FSH secretion in rat pituitary cells in primary culture. Incubation of pituitary cells with 1 nM activin A for 48 hrs resulted in an increase in FSH release into incubation medium. The effect of activin A was dependent on cell-density and the higher the density, the smaller the stimulatory action of activin A. Somatostatin, by itself, did not affect the FSH secretion. When 100 nM somatostatin was included together with activin A or the cells were pretreated with somatostatin for 2 hrs, the activin A-induced FSH secretion was enhanced. This potentiation effect of somatostatin was inversely dependent on the cell-density. These results indicate that somatostatin enhances, rather than inhibits, the activin A action in pituitary cells.