Studies in the renal handling of insulin in juvenile diabetics.

A technique is described for the accurate radioimmunoassay of insulin in serum and urine. This method was applied to study of renal clearance and excretion of endogenous and exogenous insulin in untreated juvenile diabetics and healthy young adults. There was good agreement between our results for normal adults and previously reported values. In six non-obese juvenile diabetics, urinary insulin clearance values, both basal (fasting) and following glucose loading (entire range 0.03 ml/min to 1.23 ml/min) were similar to those obtained for the adults (entire range 0.17 ml/min to 2.35 ml/min). The basal urinary excretion in these diabetics was generally of the same order of magnitude as that in the normals. The clearance of exogenous insulin, administered for the first time, was also of the same order as that for endogenous insulin. Markedly elevated urinary clearance and excretion of insulin during fasting and non-fasting states was demonstrated in four non-obese juvenile diabetics with no clinical evidence of abnormal proteinuria, though they demonstrated slight to mild clinical dehydration and acidosis compared with the other diabetics studied. Clearance and excretion of exogenous insulin was similarly elevated. This finding could reflect renal tubular dysfunction in these diabetics, and this dysfunction could relate to even the mild degree of dehydration and acidosis found in this study. Endogenous and exogenous insulin clearance in an obese diabetic child was similar to that for the control group.