Insulin binding and action on bovine adipocytes.

The present study was undertaken to determine whether bovine adipocytes could bind and respond to insulin. Adipose tissue from young bulls showed little response to physiological and higher concentrations of insulin over a 3-h incubation. In contrast, insulin did 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 about 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. In summary, 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.