QUANTITATIVE ASSAY OF INSULIN IN BLOOD PLASMA IN NORMAL AND ALLOXANIZED DOGS BY RAT DIAPHRAGM METHOD

The hemidiaphragm technique has been critically examined as a quantitative assay for small amounts of insulin, to determine the insulin activity in plasma. It was found that over the range of insulin concentration 0.01-10.1 milliunits per ml. there was a linear regression between the extra glucose uptake of the hemidiaphragms and log-concentration of insulin added to the incubation medium. The slope of this regression line was 0.751 and the standard deviation of the points about the standard regression line was 0.212. The index of precision was 0.270. The extra glucose uptake by the isolated rat diaphragm in various dilutions of plasma was determined. Occasionally, the values calculated from the responses to two-fold dilutions were found to be low, while those to twenty-fold and two hundred-fold dilutions were always identical with each other. The possible reasons for this difference were discussed briefly and it was concluded that over twenty-fold dilutions of plasma should be used for the assay of the insulin activity in plasma. By this technique the insulin activity of plasma taken from normal and alloxanized dogs was determined. The insulin activity of plasma was found to be 0.27 x 0.11 mu. per ml. in normal fasted dogs, 2.30 ± 0.41 mu. per ml. in dogs 4 hours after the injection of alloxan, and 0.00 mu. per ml. 48 hours later.