Insulin binding to liver plasma membranes from growing ruminating sheep. Maintained on different diets

The purpose of this work was to investigate insulin receptors in growing ruminant sheep given a control diet or undergoing nitrogen restriction. Live weights ranged within 30-36 kg in both groups. Before the animals were fed (i.e. at 8 a.m.) blood insulin was not significantly different in the two groups (0.39 vs 0.53 nM in experimentals and controls, respectively). The 125I-monoiodoinsulin binding to purified liver plasma membranes was studied. Membrane recovery and purity were similar in both groups. Results showed that specific 125I-iodoinsulin binding increased with time and reached a maximum value within 60-120 min. Increasing the nonlabelled insulin level inhibited 125I-iodoinsulin binding at steadystate. Among the animals from both groups, specific insulin binding decreased significantly with increased live weight. In addition, specific insulin binding lowered with increasing blood insulin. The latter relationship partly reflected the insulin binding-live weight-blood insulin relationships. The insulin binding was similar in both groups. Furthermore Scatchard analysis indicated no significant differences between apparent affinity constants and apparent binding capacities in the two groups.