Effects of growth hormone (GH)-releasing hormone and its analogs on GH secretion from cultured adenohypophysial cells in cattle

The effects of the human growth hormone (GH)-releasing hormone (hGRF(1-44)-NH2: hGRF-44), bovine GRF (bGRF(1-44)-NH2: bGRF-44), and their analogs (hGRF(1-29)-NH2, [D-Ala(2)]-hGRF(1-29)-NH2, bGRF(1-29)-NH2, [D-Ala(2), Ala(15)]-bGRF(1-29)-NH2) as well as rat GRF (rGRF) on bovine GH release from anterior pituitary (AP) cells were studied in vitro in steers. The AP cells were incubated for 2 hr with the GRFs after preincubation for 3.5 d. Both of the hGRF-44 and hGRF(1-29)-NH2 (hGRF-29) significantly stimulated GH release from cultured cells at doses from 10(-14) to 10(-8) M (P < 0.01). The analog [D-Ala(2)]-hGRF-29 significantly induced GH release in media at doses from 10(-18) to 10(-8) M (P < 0.01). The bGRF-44, bGRF(1-29)-NH2 (bGRF-29), and [D-Ala(2), Ala(15)]-bGRF-29 significantly induced GH release in media at doses as low as 10(-18) 10(-17), and 10(-16) M, respectively (P < 0.01). At doses from 10(-11) to 10(-8) M, there were no significant differences in GH-releasing potency between the hGRFs and bGRFs. The rGRF significantly stimulated GH release at doses ranging from 10(-14) to 10(-8) M (P < 0.01). The linear regression tests showed that the hGRFs, bGRFs, and rGRF, at doses from 10(-14) to 10(-8) M, induced GH release in a dose-related manner (P < 0.01). These results suggest that the hGRF, bGRF, and their analogs, as well as rGRF, are potent secretagogues of GH release from adenohypophysial cells in vitro in cattle. (C) Elsevier Science Inc. 1997.