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) s ecretion caused by feeding or the intraruminal infusion of an acetate, propionate, and butyrate mixture (107 and 214 mu mol . kg(-1) . min(- 1) over 6 h) was examined in ovariectomized ewes. Intraruminal infusio n at the rate of 107 mu mol . kg(-1) . min(-1) increased peripheral pl asma short-chain fatty acid (SCFA) concentrations to approximately the physiological levels noted after feeding. Plasma GH was markedly supp ressed by feeding and at both the 107 and 214 mu mol . kg(-1) . min(-1 ) SCFA infusion rates; however, cholinergic blocking agents completely blocked the suppressed GH secretion after feeding and only at the 107 mu mol . kg(-1) . min(-1) infusion rate. Plasma glucose increased at both infusion rates, and the plasma free fatty acids decreased after f eeding and at both infusion rates. However, both metabolites were unch anged relative to the saline control after the injection of the cholin ergic antagonists. It is suggested that the decrease in plasma GH obse rved after feeding and a near-physiological ruminal SCFA increment is mediated via the parasympathetic nerve and not by pharmacological rumi nal SCFA increments attributed to other pathways.