Influence of vitamin B-12 status on hepatic propionic acid uptake in sheep.
Pregnant ewes were fed a depletion diet low in cobalt (0.06 ppm) for 3 1/2 months. Chronic catheters were implanted 8 weeks postpartum and 7 experiments were performed on these nonlactating vitamin B-12-depleted sheep (de-B12: 340 +/- 30 ng vitamin B-12 per gram wet liver) prior to repletion by intramuscular injection of hydroxocobalamin. Six experiments were then repeated after vitamin B-12 repletion (re-B12: 2220 +/- 50 ng vitamin B-12 per gram wet liver). The hepatic extraction ratios (HER) in continuously fed sheep were 0.81 and 0.77 for de-B12 and re-B12 corresponding to net hepatic uptakes of 460 +/- 50 and 440 +/- 40 mumol propionate per minute, respectively. Continuous infusion of unlabeled propionate into a mesenteric vein at 1 mmol/minute reduced the HER, yet this depression was greatest for re-B12 (0.74 vs. 0.63 for de-B12 and re-B12, respectively). Net hepatic uptake of propionate was increased (1145 +/- 100 vs. 985 +/- 95 mumol/minute, respectively), although vitamin B-12 status was without effect. It is concluded that the ability of liver to extract propionate is not affected at vitamin B-12 concentrations greater than 250 ng/g wet liver. However, when propionate entry rate was enhanced by intramesenteric infusion, the livers of de-B12 sheep had a greater capacity to remove propionate suggesting that alternate routes of metabolism may occur.
D000818:Animals; D007263:Infusions, Parenteral; D008099:Liver / Q000378:metabolism*; D011422:Propionates / Q000008:administration & dosage / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*; D012757:Sheep Diseases / Q000378:metabolism; D014805:Vitamin B 12 / Q000502:physiology*; D014806:Vitamin B 12 Deficiency / Q000378:metabolism / Q000662:veterinary
D011422:Propionates; C029658:propionic acid; D014805:Vitamin B 12