Diabetologia
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A simple and sensitive human proinsulin radioimmunoassay system was developed using guinea pig anti-proinsulin serum, which cross-reacted neither with human insulin nor C-peptide. The recognition site of the antiserum seems to be located near the junction between the B chain and C-peptide. With this assay system, we studied the serum proinsulin concentration at fasting and after an oral 100 g glucose load in 25 healthy subjects, 21 subjects with impaired glucose tolerance and 40 patients with Type 2 (non-insulin-dependent) diabetes mellitus. ⋯ Diabetic patients with high fasting plasma glucose had a very poor insulin response, but the proinsulin response was similar to control subjects. There was a linear correlation between summed proinsulin values and summed insulin values, but the slope of the regression line was steeper in diabetic patients than in control subjects. There was a relative increase in serum proinsulin both in subjects with impaired glucose tolerance and diabetic patients.(ABSTRACT TRUNCATED AT 250 WORDS)