Plasma levels of proinsulin, insulin and C-peptide in chronic renal, hepatic and muscular disorders.

Proinsulin, insulin and C-peptide levels were investigated in chronic renal, hepatic and muscular disorders. The proinsulin levels in human plasma were determined by radioimmunoassay using insulin-degrading enzyme (IDE). The fasting levels of proinsulin in 29 patients with chronic renal failure (0.95 +/- 0.05) were significantly higher than those in 10 patients with liver cirrhosis (0.46 +/- 0.04), six with muscular dystrophy (0.37 +/- 0.02) and 52 normal subjects (0.24 +/- 0.02 ng/ml, mean +/- S.E.). The fasting levels of insulin and C-peptide in chronic renal failure were also the highest among these groups. The insulin levels in liver cirrhosis and muscular dystrophy were significantly greater than those in normal subjects and increased molar ratios of proinsulin to total insulin immunoreactivity in chronic renal failure were observed. These results suggest that the kidney, liver and muscle are related to circulating insulin levels and that the kidney plays a particularly important role in circulating proinsulin levels. It can be concluded that increases in these peptides are due to a hypersecretion of B-cells, a decreased degradation or excretion.