Insulin Binding and Action on Bovine Adipocytes

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Abstract
Whether bovine adipocytes could bind and respond to insulin was studied. Adipose tissue from young bulls showed little response to physiological and higher concentrations of insulin over a 3 h incubation. Insulin did not stimulate glucose uptake during prolonged incubations and also increased the activity of pyruvate kinase; in each case, half-maximum stimulation was observed with concentrations of .apprx. 0.5 ng/ml. Specific binding of [125I] iodoinsulin to bovine adipocytes was observed; the binding capacity was greater than that of young female rats determined under the same conditions. Bovine adipocytes internalized insulin. Incubation of bovine adipocytes with insulin resulted in a concentration-dependent loss of insulin receptors from the adipocyte surface. Bovine adipocytes possess the capacity to both bind and respond to insulin; these findings are discussed in relation to a recent report to the contrary.