Endogenous ghrelin released in response to endothelin stimulates growth hormone secretion in cattle

Abstract The purpose of this study was to evaluate whether circulating ghrelin and growth hormone (GH) concentrations in cattle are regulated by endothelin-1 (ET-1), endothelin-3 (ET-3), and secretin. Six Holstein steers (242 ± 1 d old, 280.5 ± 4.4 kg body weight [BW]; mean ± SEM) were allocated randomly in an incomplete Latin square design to receive each of 4 treatment compounds (vehicle, ET-1, ET-3, and secretin) with 1-d intervals between successive treatments. The treatment compounds were injected intravenously via a catheter inserted into the external jugular vein of each steer. Blood was sampled from the indwelling catheter at -30, -15, 0, 5, 10, 15, 20, 30, 45, 60, 90, 120, 150, and 180 min. Plasma ghrelin and GH responses to the treatment compounds were measured by a double-antibody radioimmunoassay system. Data were analyzed by using a MIXED procedure of SAS, version 9.1. Plasma acyl ghrelin, total ghrelin, and GH concentrations were increased by both ET-1 and ET-3 injection (ET-1 injection: 311 ± 15 pg/mL vs 245 ± 15 pg/mL, 2.4 ± 0.2 ng/mL vs 1.61 ± 0.05 ng/mL, 4.73 ± 0.92 ng/mL vs 1.17 ± 0.09 ng/mL for acyl ghrelin, total ghrelin, and GH, respectively; ET-3 injection: 337 ± 27 pg/mL vs 245 ± 15 pg/mL, 2.6 ± 0.1 ng/mL vs 1.61 ± 0.05 ng/mL, 5.56 ± 0.97 ng/mL vs 1.17 ± 0.09 ng/mL for acyl ghrelin, total ghrelin, and GH, respectively; P in vivo in cattle.