MEASUREMENT OF SMALL QUANTITIES OF INSULIN-LIKE ACTIVITY USING RAT ADIPOSE TISSUE. II. EVALUATION OF PERFORMANCE*

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Abstract
The characteristics of the biological assay method which utilizes the production of C14O2 from glucose-1-C-14 by the epididymal fat pads of rats to measure minute quantities of "insulin-like activity" (ILA) were studied by analyzing results obtained under routine laboratory conditions over a period of 25 months. All of the 102 routine assays with tissues from 3 rats and the current assay design had significant slopes. Results based on tissues of more than 500 rats were relatively reproducible, without evidence of important interassay error. The inherent precision of individual assays compares favorably with that of other biological methods presently in use; for example the mean index of precision [lambda][plus or minus] its standard deviation in the latest series of 55 assays, with standard insulin in concentrations of 31 and 500 mi-crounits per ml, was 0.23 [plus or minus] 0.09. Since 6 different combinations of substances and doses may be compared within each rat, several unknowns may be assayed together against a standard curve obtained at the same time. Estimates of ILA in indiluted human blood sera as well as some dilution studies, illustrate the possible applicability of the procedure to complex biological samples.