Insulin Extraction from the Renal Peritubular Circulation in the Chicken

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Abstract
The chicken has a renal portal circulation with a variable amount of hind limb venous blood draining into the post-glomerular circulation before entering the systemic circulation. By injecting [125I]iodoinsulin into a saphenous vein labeled hormone was delivered directly into the peritubular circulation on the same side. At intervals up to 6 min after the injection of [125I]-iodoinsulin, total radioactivity per gram wet weight of kidney was 63% greater on the injected side as compared to the opposite side. Similarly immunoprecipitable radioactivity (less than 4% of total radioactivity) was 55% greater on the injected side. The difference between the 2 sides represents the accumulation of insulin extracted from peritubular blood during its 1st passage through the kidney. Since most of the difference in radioactivity between the 2 kidneys was not precipitable with insulin antibody, it is evident that degradation of extracted insulin must occur. That [125I]iodoinsulin accumulates in and is degraded by the kidney following its extraction from peritubular vessels suggests that loss of insulin in renal lymph is minor. Extraction of insulin from the peritubular circulation followed by its degradation in the kidney contributes significantly to renal insulin metabolism.