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 (PACA P) on growth hormone (GH) release was compared with that of prostaglan din E(2) (PGE(2)) and growth hormone releasing factor (GRF) from cultu red bovine anterior pituitary cells in vitro. Both PACAP and PGE(2) st imulated GH release at concentrations as low as 10(-9) and 10(-8) M, r espectively, (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 contr ols were not significantly different among GRF, PACAP, and PGE(2) at 1 0(-7) M; however, the increases of GH by the 10(-8) M GRF, PACAP and P GE(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 somato statin (SS) were added together, the GH releasing effect of GRF was bl unted (P<0.01). Similar bluntness were observed in PACAP and PGE,, whe n SS was added. The stimulatory effects of GRF and PGE(2) together wer e similar to that by either GRF or PGE(2) alone. When GRF and PACAP we re added together, the GH released by both secretagogues was greater t han that by PACAP alone (P<0.01); however, a synergistic effect was no t clear when compared with GRF alone. These findings suggest that PACA P and PGE(2) may modulate the release of GH in cattle.