Existence in fetal and adult rat of several forms of material reacting with anti-insulin antibody (IRI).

The double antibody procedure detects 3 peaks in the elution fractions of adult or fetal rat sera, after passage on Sephadex G50 or G100 columns. Peak A (apparent MW 6000) contains insulin monomer; peak B (apparent MW 10-12000) is tentatively attributed to proinsulin (or proinsulin like substances); peak C (apparent MW 50-100000) is similar to the so called "big big" insulin. During intravenously induced hyperglycemia, the 3 peaks show parallel increases, but, after the disappearance of peaks A and B in streptozotocin treated rats, peak C remains unaltered. Pancreatic extracts and secreta present a very minor and inconstant peak C, the bulk of their immunoreactive material belonging to peaks A and B. A companion paper further discusses the nature of peaks B and C materials.