Evidence for independent regulation of human erythrocyte and adipocyte insulin receptors.

Specific binding of [125I]-insulin was measured in erythrocytes and fat obtained at the time of mastectomy in twenty-three subjects. There was a significant negative correlation between the level of specific binding to fat and fasting insulin concentration (r=0.55, p less than 0.05, n=23) suggesting down-regulation of fat insulin level by insulin. Insulin binding to erythrocytes did not correlate with insulin nor was there any relationship between insulin binding to erythrocytes and fat from the same subject. Thus while the erythrocyte insulin receptor may be of interest in its own right, it may not be subject to the normal regulatory influences seen in classical insulin target tissues. Insulin binding to erythrocytes may therefore be invalid as a model to study down-regulation of insulin receptors.