Role of insulin and glucose on metabolite uptake by the hind half of beef steers

Arterial and venous concentrations, extraction ratios and uptake of glucose, L-lactate and volatile fatty acids were measured in the hind half of four beef steers (340 to 360 kg) fitted with indwelling catheters in the posterior aorta and vena cava. The steers were fed hourly a pelleted, 85% concentrate diet. Treatments were control, iv infusion of insulin (1.4 IU/min) and iv infusion of glucose (149.4 mmol/h). Arterial blood concentration of glucose decreased from 3.23 mM (control) to 1.51 mM (insulin), then increased to 4.29 mM (glucose). Extraction ratio of glucose increased about threefold from 2.6 and of L-lactate decreased about fourfold from 9.2 during insulin infusion, then returned toward control values during glucose infusion. Extraction ratios of acetate (39), propionate (45) and butyrate (28) were similar among treatments. Uptake (two steers) of glucose from blood (mmol/h) increased from 38 (control) to 76 (insulin) and 99 (glucose). Uptake of acetate, propionate and butyrate from plasma (mmol/h) was, respectively, 105, 6.5, .93 (control); 170, 11.9, 3.53 (insulin) and 134, 10.9, 3.12 (glucose). Rates of uptake of glucose and propionate during control were slower (P less than .05) than rates during insulin or glucose infusion; nonsignificant changes in uptake of butyrate followed a similar pattern. Uptake of L-lactate tended to be inversely related to uptake of glucose. Treatments did not affect uptake of acetate or valerate. Uptake of all metabolites except valerate was positive, indicating net use by the hind half.