Insulin action and glucose metabolism in sheep fed on dried-grass or ground, maize-based diets

Abstract

I. The effect of an exogenous supply of glucose, provided by the digestion of maize starch in the small intestine, on endogenous glucose metabolism and insulin action was studied in sheep using the euglycaemic insulin clamp procedure.2. Insulin was infused intravenously at rates of 0.2, 0.5, 1.0 and 6.0 mU/min per kg live weight for four consecutive periods in each of four sheep fed on dried-grass and maize-based diets. Glucose was also infused intravenously at a variable rate, sufficient to maintain the plasma glucose concentration at basal levels. Whole-body rates of glucose metabolism were determined using a continuous infusion of [6-3H]glucose.3. From the resultinginsulin dose-response curves, it was observed that, when the sheep were fed on the dried-grass diet, the responsiveness of glucose metabolism to insulin was less than that reported for non-ruminants.4. When fed the maize-based diet, the glucose metabolic clearance rates (MCR) observed during insulin infusions were significantly greater (P < 0.05) than those observed for the dried-grass diet. However, after correcting for the non-insulin-mediated glucose disposal, differences between diets were not significant. 5. The sensitivity of glucose utilization to insulin was not affected by diet. The plasma insulin concentrations causing half-maximal insulin-mediated glucose MCR were 103 (SE 21) and 85 (SE 11) mU/l for the dried-grass and maize-based diets respectively. 6. The sensitivity of endogenous glucose production to insulin was also unaffected by diet. The plasma insulin concentrations resulting in the suppression of endogenous glucose production to half the basal level were 80 (SE 26) and 89 (SE 29) mU/l for the dried-grass and maize-based diets respectively. 7. It is concluded that the observed increase in glucose utilization on the maize-based diet was due partly to a slight change in responsiveness to insulin and also partly to a change in the rate of non-insulin-mediated glucose disposal.

Effect of supplemental calcium propionate on insulin action to blood glucose metabolism in adult sheep

“…In the glucose clamp procedure, blood GTR increased with increased insulin infusion rates in a dose-dependent manner as reported previously [15,33,34]. This reflected enhanced glucose utilization in insulin dependent tissues such as skeletal muscle and adipose tissue [35].…”

“…Sano et al [21] obtained a similar ratio to the present experiment in sheep. On the contrary, Janes et al [15] reported that in sheep, the EGPR was completely suppressed during the hyperinsulinemic euglycemic clamp procedure at 6 mU·kg -1 BW per min of insulin infusion. Bergman et al [33] also reported that in sheep, complete suppression of endogenous glucose appearance rate occurred at insulin concentrations of 50 to 300 μU·mL -1 .…”

“…The hyperinsulinemic euglycemic clamp procedure was applied to determine blood glucose metabolism in response to insulin infusion [12,15]. Insulin (64 and 400 U·L -1 of saline solution for two lower and two higher infusion rates, respectively; Actrapid monocomponent porcine insulin, Novo Industri, Denmark) was infused over four sequential 2-h periods at rates of 0.64, 1.6, 4.0 and 10 mU·kg -1 BW per min by another peristaltic pump through the same jugular catheter during the last 8 h of [U- 13 C]glucose infusion.…”

Combined effect of salinomycin and feeding on whole body glucose kinetics in sheep fed a high-concentrate diet

“…Endogenous glucose production was suppressed by 30 to 60% and glucose utilization was stimulated by 0 to 30% when plasma insulin concentration was increased to twofold that of basal states by insulin infusion with a maintained plasma glucose concentration [29][30][31]. This suggests that the increase in plasma insulin concentration during the postfeeding period in the present study should produce a decrease in glucose entry and no change or a slight increase in glucose utilization.…”

“…However, the mechanism is unclear as well as that of a possible increase in insulin-independent glucose utilization with feeding. Research may be needed for elucidating the mechanism, because insulin-independent glucose utilization accounts for over 80% of total glucose utilization in ruminants in a basal state [29].…”