Studies on the control of gluconeogenesis in sheep: effect of glucose infusion

Abstract

1. Effect of glucose infusions on the rate of gluconeogenesis, as indicated by changes in the irreversible loss of plasma glucose, synthesis of glucose from ruminal propionate or fixation of blood bicarbonate into glucose, has been examined in sheep.Sheep, feeding at hourly intervals, received intravenous infusions of [U-14C]glucose, NaH14CO3, or [6-3H]glucose, infused simultaneously with an intraruminal infusion of [2-14C]propionate. Glucose (4–144 mg/min) was infused intravenously at a single rate or at two different successive rates of equal duration. The glucose infusions were over a 6 h period and followed estimates of pre-infusion kinetic measurements.2. The infusion of glucose suppressed endogenous glucose production in direct proportion to that infused for sheep given diets of lucrene or wheat. The maximum rate of suppression recorded was equivalent to about 50–60% of the endogenous production rate of glucose.Transfer rates of carbon-14 from blood bicarbonate or ruminal propionate to plasma glucose were reduced during glucose loadings. The results indicate that administration of glucose was more effective in suppressing the synthesis of glucose from substrates other than ruminal propionate.3. The percentage of glucose carbon derived from blood bicarbonate was lower in sheep given wheat than in sheep given lucerne. It was suggested that this difference may have been due to absorption of glucose from the alimentary canal of sheep on the former ration. Approximately 8% of the wheat starch may have escaped fermentation and been absorbed as glucose in these animals.