Direct measurement of plasma proinsulin in normal and diabetic subjects

Abstract

Over 650 separate plasma samples from ninety-five subjects in whom oral glucose tolerance tests were performed were analyzed for glucose, total immunoreactive insulin (TIR) and immunoreactive proinsulin (IRP) content. These subjects were divided into seven groups: (1) young normal subjects (twenty to forty years old), (2) older normal subjects (forty to sixty years old), (3) young diabetic subjects (twenty to forty years old), (4) older diabetic subjects, normal weight (forty to sixty years old), (5) older diabetic subjects, obese (forty to sixty years old), (6) obese subjects (forty to sixty years old), and (7) borderline diabetic subjects. IRP levels, total IRP response and the ratio of IRP:TIR response were established for each group. Age apppeared to be a significant factor in influencing IRP levels in the normal subjects since the older subjects (group 2) had a significantly greater IRP response and IRP: TIR response than the younger subjects (group 1). Obesity and carbohydrate intolerance were each associated with slightly increased IRP levels, but the combination of obesity and carbohydrate intolerance was associated with marked increases in IRP levels and a significant increase in IRP:TIR response. The duration of diabetes may be important in the pattern of IRP release since rises in IRP levels after the oral intake of glucose occurred earlier (by thirty minutes) in both the young diabetic and borderline diabetic subjects (groups 1 and 7) than in the other groups.