Micro-enzyme immunoassay of vasoactive intestinal polypeptide (VIP)-like immunoreactive substance in bovine milk.

A sensitive and specific enzyme immunoassay for vasoactive intestinal polypeptide (VIP)-like immunoreactivity was developed with the use of synthetic carboxy-terminal (C-terminal) fragment (residue 11-28) of porcine VIP conjugated with beta-D-galactosidase and a second antibody-coated immunoplate. Using 4-methylumbelliferyl beta-D-galactopyranoside as a fluorogenic substrate, the minimum amount of VIP-like immunoreactive substance (VIP-IS) detectable by this method was 0.1 fmol/well (2.5 pmol/l). The level of VIP-IS in bovine foremilk was above 100 pmol/l, which was more than eightfold higher than that in normal milk.