ANTIBODY-SUPPRESSIBLE AND NONSUPPRESSIBLE INSULIN-LIKE ACTIVITIES IN HUMAN SERUM AND THEIR PHYSIOLOGIC SIGNIFICANCE. AN INSULIN ASSAY WITH ADIPOSE TISSUE OF INCREASED PRECISION AND SPECIFICITY*

Abstract

Adipose tissue has been shown to respond to insulin in vitro by several groups of investigators whose work has recently been reviewed by Jean- renaud (1).Martin, Renold, and Dagenais (2) pointed out the extreme sensitivity of adipose tis- sue to insulin.Renold, Sheps, and co-workers (3, 4) used as a metabolic index of serum insu- lin-like activity (ILA) the oxidation of glucose-1- C14 to C140,.Several investigators adopted their method with equally good results (5-7).Hum- bel (8) and others (9, 10) measured the glucose uptake of epididymal adipose tissue as an index of ILA, and Ball and Merrill (11) determined the net gas exchange.When the fat-pad assay is applied to the determination of ILA in human serum, several discrepancies become apparent be- tween its results and those obtained by other biological and immunological assay technics currently in use.The mean value of ILA in undiluted serum of fasting normal subjects approximates 50 /AU per ml by the diaphragm technic (12-14) and about 20 MU per ml by the immunological assay pro- cedure of Yalow and Berson (15).The figures obtained with the adipose tissue method are substantially higher, and vary between 30 and 1,000 MU per ml (4, 16, 17).Randle (18) and Willebrands, Van der Geld, and Groen (19) determined ILA in diluted serum with the dia- phragm and found values in the same high range as those obtained with adipose tissue.Although these discrepancies cannot be fully explained at present, the following points are relevant.1) Adrenaline, noradrenaline, ACTH, growth hor- mone, and glucagon enhance the glucose uptake of adipose tissue in vitro.In contrast to insulin, however, these lipolytic hormones do not increase