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Influence of Vitamin B-12 Status on Hepatic Propionic Acid Uptake in Sheep¹

Department of Animal Science, New York State College of Agriculture & Life Sciences ^* Department of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca, NY 14853-0281

Pregnant ewes were fed a depletion diet low in cobalt (0.06 ppm) for 3 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 µmol 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 µmol/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.

KEY WORDS: • propionate • liver uptake • vitamin B-12

¹ Presented in part at the 65th annual meeting of Federation of American Societies for Experimental Biology. Atlanta. GA, April 13, 1981. Fed. Proc. 40, 866 (1981).

² To whom reprint requests should be sent.

Manuscript received 15 November 1982.