INTRAPERITONEAL TEST OF INSULIN ACTIVITY ON THE RAT DIAPHRAGM IN VIVO: FACTORS CONTROLLING THE VARIABILITY OF RESPONSE

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Abstract
Rafaelsen's intraperitoneal assay of insulin in rats, where the effect measured is the increased incorporation of [U-14C] glucose into diaphragm glycogen, is extremely sensitive and has important advantages over techniques using muscle preparations in vitro, as well as over the more usual techniques in vivo. To make the test more precise and more reproducible from day to day, the optimal conditions have been derived from an examination of each of the principal steps of the technique and from an analysis of the data obtained over a period of 51/2 years. For comparative purposes, the response to a single concentration of insulin, 1 mU/ml, was examined throughout. The principal factors affecting the variability of response are (a) nutritional state of the rats, and (b) weight range of the animals. The proportion of experiments having high relative standard deviations was substantially reduced by fasting the rats for 24 h before the test, and ensuring that they were adequately fed immediately before the fast. It was found that insulin sensitivity changes appreciably with body weight over the complete weight range used (70 to 120 g before fasting) and, consequently, although correcting for variations in body weight reduces variability, the weight range within an individual experiment should be kept as small as possible.

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