Isolation of Porcine Vasoactive Intestinal Polypeptide and Comparison of Its Biological Activities with Secretin and Glucagon

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Abstract
In the course of purification of secretin from porcine duodenum, a fraction containing VIP(vasoactive intestinal polypeptide)-like peptide was also found. This peptide was isolated by various chromatographic techniques and was identified as VIP by several chemical and biological criteria. Some comparative studies on the typical biological activities among VIP, secretin and glucagon were done. VIP had strong hypotensive activity on rats in the threshold dose of 38 ng/kg. Secretin and glucagon showed no effect even in a high dose of 5 .mu.g/kg. VIP had a very weak activity on rat pancreatic secretion in comparison with secretin, and glucagon had no effect. VIP and glucagon had no potentiating or inhibiting effects on rat pancreatic secretion stimulated by secretin. Hyperglycemic effects of VIP on urethane-anesthetized rats were nearly equivalent to those of glucagon, whereas secretin had no effect on blood glucose. While secretin exerted no influence on isolated guinea pig ileum, VIP had a dose-dependent contractile activity and glucagon had a weak contractile activity. VIP and secretin intensively relaxed rat fundus strip in a dose of 1 ng/ml with similar potencies. VIP also relaxed guinea pig tracheal chain in a dose of 20 ng/ml, but secretin and glucagon had no effect.