Role of the Kidney in the Disposal of Radioiodinated and Nonradioiodinated Insulin in Dogs

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Abstract
Insulin concentration in each sample of dog urine, carotid artery plasma, or renal vein plasma was estimated following the infusion of bovine insulin-I-125, unlabeled bovine insulin, or glucose. Insulin was estimated by immunoassay and by TCA insoluble radioactivity. Whenever insulin-I-125 and unlabeled insulin were infused together both methods were used on each sample. In agreement with the conclusions of others, who have used less direct technics, it was found that the use of plasma TCA insoluble radioactivity to determine radioinsulin degradation in vivo results in an underestimate of insulin removal, and hence an overestimate of insulin half life. This finding was shown to apply not only to the whole animal but also the kidney. All forms of insulin were removed by the kidney but the radioactive estimate of kidney insulin removal was less than that by immunoassay. Data from experiments in which radioactive insulin was bound to guinea pig anti-insulin serum prior to infusion and from experiments in which ureteral ligation was performed prior to infusion indicated that the kidney removed insulin primarily by glomerular filtration but that direct absorption also played a role.