Number and affinity of insulin receptors in intact human subjects.

A simple model of the distribution and metabolism of insulin in vivo has been evaluated using data from insulin infusion into a group of normal subjects. The major rate-limiting step for access to degradation pathways is assumed to consist of binding of the ligand to a single population of insulin receptor sites, except that provision is made for the possibility of linear non-receptor-mediated degradation and for the phenomenon of negative cooperativity. The model has been shown to accommodate the non-linearity of insulin metabolism, allows, evaluation of receptor association and dissociation constants and provides for the first time an estimate of total accessible receptor number in the intact organism. For normal fasting man the model predicts 1.00 +/- 0.05 nmol accessible binding sites/kg (mean +/- SD).