Radioimmunoassays for Human, Pork and Ox C-peptides and Related Substances

Summary

Antibodies reacting with ox, pork and human C-pep-tide have been prepared using ox and pork proin-sulin and human b-component as the immunogens. Specific assays for C-peptide and/or proinsulin-like substances were established by using ¹²⁵I-Tyr-C-peptide as tracer. In solutions (serum and pancreatic extracts) containing C-peptide, proinsulin and insulin, the two latter substances were bound by addition of insulin antibodies and separated from C-peptide by ethanol precipitation. Thus the determination of C-peptide could be performed on the supernatant without interference from proinsulin. Pancreatic extracts were found to contain equimolar amounts of insulin and C-peptide, whereas proinsulin constituted about 3% (molar) of the total IRI. After i.v. injections of glucagon, equimolar amounts of insulin and C-peptide were found to be secreted into venae pancreatico-duodenales. The average concentration of C-peptide in serum from 9 normal persons was found to be 0.33 ± 0.05 pmole/ml. After oral administration of 1.75 g glucose per kg, the value increased to 2.3 ± 0.3 pmole/ml.