Regulation of release of somatotropin from in vitro cultures of bovine and porcine pituitary cells.

Bovine and human GH releasing factors (GHRF), in concentrations ranging from 10 pM to 10 nM, stimulated GH release from cultured bovine and porcine anterior pituitary cells. Agents that increase intracellular cAMP levels (e.g. isobutylmethylxanthine and 8-bromo-cAMP) also stimulated bovine and porcine GH release. Somatostatin, in doses ranging from 1-100 nM, inhibited both basal and GHRF-stimulated GH release from the bovine pituitary cultures, and 100 nM somatostatin inhibited GHRF-stimulated release of porcine GH. Addition of exogenous bovine GH suppressed basal, but not GHRF-stimulated, release of bovine GH. Human insulin-like growth factor I did not suppress basal or GHRF-stimulated release of bovine GH from bovine pituitary cells, although it has been confirmed in this report that insulin-like growth factor I suppresses stimulated release of GH from rat cells. Furthermore, the GH release peptides described by Momany et al. stimulated little or no GH release from bovine or porcine pituitary cell cultures, in contrast to their activity in rat cells. The results show that whereas some regulatory features of GH release from bovine, porcine, and rat pituitary cell cultures are similar, others differ significantly.