MOLECULAR VARIANTS OF VASOACTIVE INTESTINAL POLYPEPTIDE IN DOG, RAT AND HOG

Molecular forms of vasoactive intestinal polypeptide (VIP) were studied in the gut and brain of dog, rat and hog. Fractionation of acid extracts on CM-Sephadex revealed 3 components cross-reacting in a radioimmunoassay using an amino-terminal specific antiserum. One of the components was compatible with standard porcine octacosapeptide VIP; the other two eluted earlier and are so likely to be less positively charged peptides. After gel filtration on Sephadex G50, the same peaks of activity eluted in a similar position to porcine VIP, indicating similar molecular size. There were marked species differences in the distribution of the different molecular forms. In both muscle and mucosal layers of the rat intestine, 50-90% of total immunoreactive VIP was due to the molecular variants; in hog colon the variants were found predominantly in the mucosa and accounted for .apprx. 50% of total immunoreactivity. A form of VIP compatible with the authentic peptide accounted for over 75% of activity in the brain of all 3 spp. The biological activity of the VIP variants is not known and caution should be taken in interpreting the physiological significance of studies on the action, release and metabolism of VIP.