PLASMA PROINSULIN IN RECENTLY DIAGNOSED TYPE-2 DIABETES-MELLITUS

We measured levels of immunoreactive insulin (IRI) and proinsulin usin g a sensitive and specific immunoradiometric assay (IRMA), in non-obes e recently diagnosed type 2 diabetic subjects. The proinsulin IRMA sho wed full cross reaction with intact proinsulin, des 31-32 proinsulin a nd des 64-65 proinsulin, but no reaction with insulin or C-peptide. In a group of 41 recently diagnosed non-obese Caucasian type 2 diabetic subjects (study group), mean fasting proinsulin levels were greater th an that of 40 age and body mass index (BMI) matched controls (study gr oup 17.4 +/- 2.0, controls 10.1 +/- 0.9 pmol-1, P < 0.001). Following a standard test meal, 30 and 60 min levels were not significantly diff erent between groups but 90- and 120-min proinsulin levels were elevat ed in the study group. The maximum proinsulin to IRI ratio was 20% in the fasting state and did not differ between study and control groups. Proinsulin profiles were similar in subjects receiving oral hypoglyca emic agents and those on dietary treatment alone. Proinsulin did not c orrelate with indices of glycaemic control, total cholesterol, triglyc erides or HDL cholesterol, but a relationship was observed with IRI be fore and after the meal. These results suggest that increased secretio n of insulin precursors of low biological activity occurs in non obese recently diagnosed type 2 diabetic subjects under reasonably good gly caemic control; in such individuals the elevated levels of these precu rsors are approximately in proportion to the increase in IRI and are l ess than those reported in some previous studies.