Effects of cold exposure and time relative to feeding on glucose metabolism of sheep using a glucose clamp approach

Abstract

An experiment combining a hyperinsulinaemic euglycaemic clamp approach and an isotope dilution method determined the effects of cold exposure and time relative to feeding on blood glucose metabolism in four sheep. The sheep, fed 20 g/kg body-weight (BW) of lucerne hay cubes and 5 g/kg BW of maize-based concentrates once daily, were exposed in turn to a thermoneutral environment (20 °C) and a cold environment (0 °C) for 20 days. The combined experiments were performed at four different times relative to feeding, i.e. 3 to 2 h, 2 to 1 h and 1 to 0 h before, and 1 to 2 h after the initiation of feeding for the basal periods, and 1 to 0 h before, and 0 to 1 h, 1 to 2 h and 3 to 4 h after the initiation of feeding for the glucose clamp periods in both environments. [U-¹³C]Glucose was continuously infused for 6 h after a priming injection. Insulin was continuously infused at 6·0 mU/kg BW per min for 2 h, which corresponded to the last 2 h of the [U-¹³C]glucose infusion. Blood glucose concentrations were maintained euglycaemic during the insulin infusion by concomitant variable glucose infusion. Blood glucose turnover rate (GTR) during the basal period was enhanced by cold exposure (P=0·01) and feeding (P=0·04). Blood GTR increased (P<0·01) with the glucose clamp. During the glucose clamp, blood GTR and glucose infusion rate (GIR) were greater (P=0·003 and P=0·001, respectively) during cold exposure than in the thermoneutral environment. Time relative to feeding influenced (P=0·003) the GIR, whereas changes in blood GTR and endogenous glucose production rate were not significant. No significant cold×feeding interaction was observed in these variables. It was suggested that, in sheep, glucose metabolism was enhanced by cold exposure and the glucose clamp. It was probable that blood glucose metabolism during the glucose clamp was influenced by cold exposure and feeding, but the combined effect of cold exposure and feeding was not significant.