Insulin assay using mice

The studies on the insulin receptor of human lymphocytes led to the development of a sensitive radioreceptor assay which complements the radioimmunoassay in measuring minute quantities of substances in plasma with insulin bioactivity. Using this technique clinically, a patient with a primary defect in insulin receptor deficiency was reported . In the same study, acquired and reversible receptor deficiency was also observed in obese patients . In the obese-hyperglycemic mutant mouse, insulin-resistance appears to correlate directly with an irreversible deficiency in insulin receptor activity on the adipocyte and hepatocyte plasma membranes. Cuatrecasas and his co-workers, on the other hand, reported the same number of insulin-binding sites in adipocytes from obese and insulin-resistant rats as were present in those from normal animals They proposed that the metabolic defect in these animals resides in the coupling of the signals of the insulin-receptor complex to glucose transport. 

Morris et al. (495) observed a Cr(III) dependent increase in 2-deoxyglucose uptake by cultured mouse myotubes in the presence of insulin. The effect was caused by the addition of nanomolar concentrations of CrCl3 to the reaction medium [a standard minimal essential cell culture medium, containing amino acids, mineral salts, and glucose, which was purified with Chelex resin to remove trace heavy metal ions before the addition of Cr(III)]. The same Cr free medium was used for cell growth [growing the cells in the presence of a trace amount of Cr(III) reduced their sensitivity in the assays]. Thus, unlike the previous studies (491), an apparent insulin-potentiating effect of CrCls was demonstrated. However, Cr(III) most likely formed complexes with amino acids of the medium (80), which prevented its hydrolysis in a neutral aqueous solution and made it more available to the cells. 

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