A method utilizing serial incubations of paired rat hemidiaphragms has been developed. In this technic, two basal glucose uptakes and two uptakes in the presence of insulin can be determined in a single rat, thus eliminating rat to rat variations when comparing two insulin effects. This system, particularly useful for the study of insulin antagonism, was applied to the assay of the albumin-associated antagonist in various human and commercial preparations. The presence of higher concentrations of this antagonist in untreated adult-onset diabetes was confirmed in two out of three diabetic patients tested. Albumin from a third diabetic patient was stimulatory. Varying amounts of antagonism were found in the commercial albumin preparations. Evidence is presented suggesting that total bound FFA do not play an important role in the albumin-associated insulin antagonism.

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