Abstract
Summary
1. Procedures for routine preparation from rat serum of fractions uniformly inhibitory to glucose uptake of rat diaphragm have been developed; it was possible to obtain such fractions not only from diabetic rat serum, as previously reported, but also from normal rat serum. Inhibitory activity of fractions from normal serum was enhanced by prior treatment of serum donor with pituitary growth hormone; adrenocorticotrophic hormone or thyrotrophic hormone had no such effect. 2. Inhibitory fractions had gross properties of β-lipoproteins and could be prepared free of lipides having electrophoretic mobility of albumin or α-globulins. Average ratio of total lipide to protein was .25 for fractions from diabetic rat serum and .11 for fractions from normal rat serum; phosphatide/total lipide ratio was lower in such fractions than in parent sera. Relation of inhibitory activity to lipide content requires further clarification, as inhibitory activity may be lost by delay during preparation of fractions without significant change of lipide content or electrophoretic behavior of fractions. 3. Inhibitory fractions interfered with stimulatory action of insulin on diaphragm muscle. The fraction from 1 ml of diabetic or normal rat serum nullified the stimulatory effect of at least .0004–.001 unit of insulin.
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