Insulin responsiveness, action and sensitivity in growing lambs and mature rams

Abstract

Insulin responsiveness, action and sensitivity, using the glucose clamp technique, were measured in ruminating growing lambs (5 and 9 mo old) and mature rams (3 yr old). In the hyperglycemic clamp experiment, blood glucose concentrations were designed to remain 50 mg dL−1 above basal concentrations for more than 1 h. Plasma insulin concentrations during glucose infusion were lower (P < 0.05) for 5 mo-old lambs than for 9 mo-old lambs and mature rams and were higher (P < 0.05) for 9 mo-old lambs than for 5 mo-old lambs and mature rams. In the hyperinsulinemic euglycemic clamp experiment, insulin was infused over five sequential 1-h periods at rates from 0.64 to 25 mU kg−1 min−1 with concomitant glucose infusion to maintain preinfusion blood glucose concentrations. Glucose infusion rates during insulin infusion were lower (P < 0.05) for 5 mo-old lambs than for 9 mo-old lambs and plasma insulin concentration at half-maximal glucose infusion rate was numerically lower for 5 mo-old lambs, whereas maximal glucose infusion rate did not differ among growth stages. It is likely that in ruminating sheep insulin responsiveness, action and sensitivity may change with growth stage. Key words: Development, insulin response, insulin sensitivity, sheep, glucose clamp technique