MEASUREMENT OF SMALL QUANTITIES OF INSULIN-LIKE ACTIVITY USING RAT ADIPOSE TISSUE. I. A PROPOSED PROCEDURE*

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Abstract
A bioassay procedure suitable for measuring small quantities of insulin or "insulin-like activity" has been presented. The procedure is based upon the responsiveness to insulin of isolated epididymal rat adipose tissue. The index selected has been that of production of C14o2 from glucose-1-C14. The method is capable of detecting 10 [mu]U of insulin per ml. An advantage of the procedure derives from the ability to compare several standard solutions and unknown samples within tissue from any one animal. It is sufficiently convenient to allow for the routine comparison of 2 standards and 4 unknown samples in each of 3 rats on any given day. The effect of insulin upon this tissue is inhibited by pretreatment with reduced glutathione or by addition of antiserum obtained from guinea pigs. Although the tissue is responsive to many metabolic agents, information available so far has failed to reveal hormonal activities other than those of insulin which are likely to interfere significantly with the determination of insulin-like activity in samples containing physiological concentrations of these activities. It is essential, however, to consider any measured activity other than that derived from added crystalline insulin as "insulin-like" until sufficient evidence can be produced to establish its identity with insulin.