Insulin Binding and Free Insulin in Serum of Insulin-Treated Diabetics

Abstract

Insulin-I¹²⁵ (0.1 ml, 0.1 microCi) was added to the equal volume of serum and fractionated on 9 × 300 mm column of Sephadex G-100 into protein-bound (B) and free (F) insulin immediately or after 24-hour incubation. When the fractionation was performed immediately, the B/F ratio was in 10 healthy persons 0.045 ± 0.006 (just like that of labelled insulin preparation itself), and in twenty-six insulin-treated diabetics 0.605 ± 0.073. After incubation B/F ratio were correspondingly 0.056 ± 0.011 and 2.021 ± 0.103. There was no overlapping between normals and diabetics (P < .001), and no protein binding of insulin by normal serum was evident. At pH 3 the bound insulin dissociated, and virtually all the radioactivity appeared with free insulin fraction. Free insulin level in the serum of diabetics as determined after serum fractionation on Sephadex G-100 was 35.8 ± 4.0 microU/ml only and did not correlate with B/F ratios; insulin dose or blood glucose. No (free)-hyperinsulinemia was found in severe insulin-treated diabetics.

Key words

Free Insulin - Insulin Antibodies - Diabetes