INVIVO DEMONSTRATION OF INSULIN-RECEPTOR DEFECT WITH I-123 LABELED INSULIN AND SCINTIGRAPHIC SCANNING IN SEVERE INSULIN RESISTANCE

OBJECTIVE - Insulin-receptor function in humans is usually studied in vitro on readily available celts, e.g., erythrocytes and fibroblasts. Although these cells are not metabolically important targets for insulin action, information derived from them are often taken as representative of other tissues. The aim of this study was to investigate insulin receptors in vitro on erythrocytes and in vivo on one of the main insulin-target organs, the liver. RESEARCH DESIGN AND METHODS - A 16-yr-old girl affected by severe insulin resistance was identified. Insulin receptor binding was measured on the erythrocytes of the patient and of 6 nondiabetic volunteers. The biodistribution of I-123-labeled insulin was studied in vivo by scintigraphic scanning in the insulin-resistant patient and in 10 nondiabetic volunteers. RESULTS - Erythrocytes of this patient displayed a markedly reduced [I-125]insulin binding. In vivo I-123-insulin biodistribution was characterized by lack of hormone uptake by the liver (4 vs. 21% of the injected dose in control subjects) contrasting with intense accumulation of radioactivity in the kidneys. CONCLUSIONS - Our studies show that defects of insulin binding can be directly demonstrated in vivo on liver receptors with a noninvasive technique with low radiotoxicity.