Effects of pituitary adenylate cyclase-activating polypeptide (PACAP), prostaglandin E 2 (PGE 2) and growth hormone releasing factor (GRF) on the release of growth hormone from cultured bovine anterior pituitary cells in vitro

Abstract

The effect of pituitary adenylate cyclase-activating polypeptide (PACAP) on growth hormone (GH) release was compared with that of prostaglandin E 2 (PGE 2) and growth hormone releasing factor (GRF) from cultured bovine anterior pituitary cells in vitro. Both PACAP and PGE 2 stimulated GH release at concentrations as low as 10 −9 and 10 −8 M, respectively, (P<0.01). However, GRF released GH at a concentration as low as 10 −13 M (P<0.01). Percent increases of GH compared with controls were not significantly different among GRF, PACAP, and PGE 2 at 10 −7 M; however, the increases of GH by the 10 −8 M GRF, PACAP and PGE 2 were 196, 118, and 27%, respectively, (P<0.01), and 124, 65, and 1% in the 10 −9 M media, respectively, (P<0.01). When GRF and somatostatin (SS) were added together, the GH releasing effect of GRF was blunted (P<0.01). Similar bluntness were observed in PACAP and PGE 2, when SS was added. The stimulatory effects of GRF and PGE 2 together were similar to that by either GRF or PGE 2 alone. When GRF and PACAP were added together, the GH released by both secretagogues was greater than that by PACAP alone (P<0.01); however, a synergistic effect was not clear when compared with GRF alone. These findings suggest that PACAP and PGE 2 may modulate the release of GH in cattle.