Measurement of proinsulin in human pancreatic juice

In this study, we measured proinsulin in human pancreatic juice by radioimmunoassay (RIA). Affinity chromatography was used to separate proinsulin and insulin from C-peptide; and high-performance liquid chromatography, to separate proinsulin from insulin. In the RIA procedure for proinsulin we used porcine insulin antiserum as the antibody and porcine proinsulin as the standard and labelled antigen. The concentrations of proinsulin in human pancreatic juice obtained 5, 10, 15 and 20 minutes after intravenous injection of secretin were 29 +/- 6, 41 +/- 4, 35 +/- 14 and 37 +/- 17 (pmol/l +/- SD, means of 7 subjects), respectively. These values were higher than those in serum from fasted subjects, 12 +/- 4 pmol +/- SD. This work shows that proinsulin is present in human pancreatic juice.