Quantitative aspects of propionate metabolism and gluconeogenesis in sheep

Abstract

Labeled propionate was infused into a rumen vein of 10 conscious sheep and blood samples were collected from the portal vein. Glucose turnover rates were measured in 4 additional experiments. The mean rate of propionate absorption into the portal system was 24 mmoles/hr. (0.45 mmole/kg/hr.) in normal sheep and about 13 mmoles/hr. in sheep fed half-rations. About 50% of the propionate was converted to glucose and 40% was synthesized to other compounds. One-fourth was oxidized to CO2 but most of this occurred after transformation to glucose. The percentage of the glucose turnover originating from propionate was only 27% in normal animals, and this was proportional to the rate of propionate metabolism. At a rate of 70-80 mmoles/hr. (1.4 mmoles/ kg/hr.), which was attained by infusion of carrier propionate, a maximum of about 65% of the glucose originated from propionate. It is concluded that protein probably accounts for much of the glucose requirements of adult ruminants and that, depending on the diet, propionate probably forms only 20-40% of the glucose.