Effect of fast and hexose injection on serum insulin concentrations of sheep

Abstract

Immunoreactive serum insulin concentration in 15 wethers fasted 16–24 hr was 126 ± 12 µU/ml. Exogenous glucose produced a tenfold increase in serum insulin within 15 min; concentrations remained high for 1 hr and then declined. Fructose increased both blood glucose and insulin. The maximum response of the latter was delayed, in comparison with that produced by glucose injection, and coincided with a rise of blood glucose derived from fructose conversion. Galactose produced a moderate and immediate rise in insulin associated with elevated blood glucose concentrations. There was a positive relationship between the amount of insulin secreted and the utilization rate of injected glucose. Thus, insulin released by glucose loading in the sheep is both immunologically and biologically active. Prolonged fasting depressed glucose tolerance and the amount of insulin secreted following glucose injection. Certain characteristics of the sheep, such as reduced glucose tolerance and low glucose oxidation, are not due to a relative lack of circulating insulin or to an inability of hyperglycemia to mobilize insulin stores.