2003 Volume 50 Issue 3 Pages 289-295
To clarify the direct effects of ghrelin on growth hormone (GH) release from anterior pituitary (AP) cells in cattle, GH-releasing effects of human ghrelin (hGhrelin) and rat ghrelin (rGhrelin) on bovine AP cells were compared with those of GH-releasing hormone (GHRH) in vitro. The AP cells were obtained from Holstein steers and were incubated for 2 h with the peptides after incubating in DMEM for 3 days. hGhrelin and rGhrelin significantly stimulated GH release from the cultured cells at doses from 10-10 to 10-7 M and from 10-9 to 10-7 M, respectively (P<0.05). The rates of increase in GH at 10-10, 10-9, 10-8 and 10-7 M hGhrelin were 26, 26, 59 and 100% compared with controls, respectively, and those of increase in GH at 10-9, 10-8 and 10-7 M rGhrelin were 58, 74 and 106%, respectively. GHRH significantly increased GH concentrations in cultured media at a dose as low as 10-13 M compared with the control (P<0.05). When hGhrelin (10-8 M) and GHRH (10-8 M) were added together, the release of GH induced by both peptides was significantly greater than that by hGhrelin alone (P<0.05), and tended to be greater than that by GHRH alone. Somatostatin (SS, 10-7 M) significantly blunted GH release induced by hGhrelin (10-8 M) and GHRH (10-8 M)(P<0.05). In the presence of SS, the percent increase in GH released with hGhrelin plus GHRH was 42% and 14% greater than that by either hGhrelin or GHRH alone, respectively (P<0.05). These results show that ghrelin directly stimulates the release of GH from anterior pituitary cells, and that SS modifies ghrelin-stimulated GH release in cattle.
