Effect of cholinergic blockade on inhibited GH secretion by feeding and intraruminal SCFA infusion in sheep

The effect of cholinergic blockade on suppressed growth hormone (GH) secretion caused by feeding or the intraluminal infusion of an acetate, propionate, and butyrate mixture (107 and 214 μmol · kg^-1 · min^-1 over 6 h) was examined in ovariectomized ewes. Intraluminal infusion at the rate of 107 μmol · kg^-1 · min^-1 increased peripheral plasma short-chain fatty acid (SCFA) concentrations to approximately the physiological levels noted after feeding. Plasma GH was markedly suppressed by feeding and at both the 107 and 214 μmol · kg^-1 · min^-1 SCFA infusion rates; however, cholinergic blocking agents completely blocked the suppressed GH secretion after feeding and only at the 107 μmol · kg^-1 · min^-1 infusion rate. Plasma glucose increased at both infusion rates, and the plasma free fatty acids decreased after feeding and at both infusion rates. However, both metabolites were unchanged relative to the saline control after the injection of the cholinergic antagonists. It is suggested that the decrease in plasma GH observed after feeding and a near-physiological ruminal SCFA increment is mediated via the parasympathetic nerve and not by pharmacological ruminal SCFA increments attributed to other pathways.