Changes of Glucose, Insulin and Glucagon Associated with Propionate Infusion and Vitamin B-12 Status in Sheep

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Abstract
The effect of propionate on hormonal and metabolic events was studied in ewes that were vitamin B-12 depleted (de-B12) and repleted (re-B12). Experiments were conducted before and after hydroxocobalamin resupplementation. De-B12 sheep had greater blood concentrations and total hepatic influx and efflux of glucose. However, rates of net hepatic release of glucose were similar. Comparable glucagon concentrations and fluxes were reduced in de-B12, but insulin values were unaffected by vitamin B-12 status. Intramesenteric infusion of propionate elevated concentrations of glucose, insulin and glucagon at nearly all samplings. Secretion of insulin was elevated at the first sampling only (15 minutes), while glucagon appeared elevated until 30 minutes. Rates of hepatic removal of hormones were not altered during infusion. Net hepatic release of glucose was increased at nearly all samplings, but de-B12 ewes had a greater increment of total hepatic influx and efflux. De-B12 ewes exhibited a diminished glucagon response to propionate infusion, whereas insulin concentrations and hepatic uptakes tended to be greater. Vitamin B-12 status, within the range usually considered normal, thus influences metabolic and hormonal responses to increased rates of propionate entry in the sheep, independent of feed intake.

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