FURTHER IMMUNOLOGICAL STUDIES ON THE FORM OF CIRCULATING INSULIN

Abstract

SUMMARY Preliminary observations of the responsiveness of the fat-pad to crystal-line insulin have shown a straight-line response to the log dose from 5 to 250 μu./ml. incubate, in respect of either 14CO2 or 14C-fat production from 14C-1-glucose in the incubate when the response is expressed as The response in this same metameter to added normal serum has shown a similar slope for additions of serum from 0·0625 to 0·45 ml./ml. incubate. In experiments on fasting dogs, venous serum has been sampled from pancreatic, hepatic and peripheral veins and assayed for insulin-like activity (i.l.a.) with and without added antibody, i.e. for total and 'atypical' i.l.a. Pancreatic venous serum contained about five times as much total i.l.a. as the other sites, but only 10% 'atypical' i.l.a., while the others contained 55—70% 'atypical' i.l.a. Similar experiments on dogs after intravenous administration of glucose showed a five- to ninefold rise in total i.l.a. in all sites, but only three- to fourfold rise in 'atypical' i.l.a. The 'atypical' i.l.a. resembled insulin in stimulating both 14CO2 and 14C-fat production and in being neutralized by cysteine, yet it could not be attributed to the added antiserum (which assayed alone could only produce < 3–12% of this activity).