Comparative studies on secretin

Abstract

The mammalian intestinal hormone secretin is related in structure to the pancreatic hormone glucagon, and to two peptides recently isolated from hog duodenum, vasoactive intestinal peptide (VIP) and gastric inhibitory peptide (GIP). Because of their structural similarities it has been suggested that these peptides evolved from a common ancester, and comparative studies may be expected to shed light on this question. In the present series of experiments pure porcine secretin was found to be a weak stimulant of the flow of pancreatic juice in a bird (the turkey) although it was a strong stimulant in mammals such as cat and rat. In contrast, pure porcine VIP had weak actions on the flow of pancreatic juice in mammals but was a potent stimulant in birds, while porcine glucagon and GIP showed no stimulatory effects on exocrine pancreatic secretion in either birds or mammals. Like VIP, extracts of the intestine of birds (chicken) and teleost fish (pike and cod) had weak secretin-like actions on the pancreas in mammals but strong actions in birds. The results indicate that in the intestines of birds and fish there are factors with biological properties similar, but not identical, to those of mammalian secretin and VIP, and it is suggested that the secretin group of hormones has a long evolutionary history.