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

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,, 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.