Glucose utilization in sheep

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Abstract
Measurement of glucose utilization in sheep by isotope dilution has indicated the central importance of glucose in sheep metabolism. Glucose utilization rates in fed and starved (24 hr.) animals, measured by a constant-infusion method, were 2.7 [plus or minus] 0.2(7) and 1.5 [plus or minus] 0.09 (13) mg/min./kg body wt. respectively. When calculated in terms of metabolic body weight (W0.6) utilization rates in starved sheep were about 75% of those reported for starved dogs. Corresponding values for the volume of distribution of the body glucose pools, expressed as a percentage of body weight, were 27 [plus or minus] 1.7(7) and 23 [plus or minus] 1.2(13). A comparison of single-injection and constant-infusion methods for the measurement of glucose-utilization rates indicated that significantly higher results were given by the former technique. Evidence of some inhibition of endogenous glucose entry under glucose load was obtained when utilization rates were measured at high concentrations of circulating glucose achieved by constant infusion. A roughly linear relationship was observed when glucose-utilization rates obtained in all constant-infusion experiments were plotted against corresponding plasma glucose concentrations. Rough estimates of the contribution of glucose to overall oxidative metabolism were obtained by a comparison of the specific activities of plasma glucose and blood CO2. The results suggested that in fed and in starved animals 22-23% and 11-19% respectively of blood CO2 was derived from glucose. Under glucose load this value rose to about 30%.