Intraruminal propionate supplementation modifies hindlimb energy metabolism without changing the splanchnic release of glucose in growing lambs

The influence of propionate supplementation on the splanchnic metabolism of energy-yielding nutrients and the supply of glucose to the hindlimb was investigated in growing lambs. Six rumen-cannulated and multicatheterized lambs (32·2 kg), fed frozen rye grass at 690 kJ metabolizable energy intake/d per kg body weight0·75, were infused intraruminally with a salt solution (control) or with propionate solutions at 0·55 mol/d (P1) or 0·98 mol/d (P2) according to a replicated Latin square design. In the rumen fluid, supplementation decreased the acetate:propionate molar ratio from 2·36:1 to 1·37:1, without modifying the ruminal concentrations of acetate and NH4. As a result, the portal appearance of propionate increased by 51 and 72 % with P1 and P2, respectively, and that of L-LACTATE DOUBLED. ACROSS THE LIVER, NET EXTRACTION OF PROPIONATE INCREASED BY 47 AND 67 % WITH P1 AND P2, RESPECTIVELY. HOWEVER, THE NET HEPATIC PRODUCTION OF GLUCOSE REMAINED UNCHANGED, PROBABLY AS THE RESULT OF A SUBSTANTIAL RISE IN INSULIN SECRETION AND ITS HEPATIC EXTRACTION. OVERALL, THE NET SPLANCHNIC RELEASE OF ACETATE, GLUCOSE AND BUTYRATE WAS NOT MODIFIED WHILE THAT OF l-lactate increased. Despite this, the net uptake of acetate, glucose, l-lactate and non-esterified fatty acids by the hindlimb increased. Propionate probably enhanced the storage of energyyielding nutrients in the hindlimb, despite their unchanged release by the splanchnic tissues and the unmodified insulinaemia. Regulatory mechanisms are not clear.