Abstract
The information available concerning the evolution of endocrine regulation of three gastrointestinal functions in lower vertebrates—gastric acid secretion, gallbladder contraction, and pancreatic enzyme secretion—is reviewed. The actions of hormones of the cholecystokinin/gastrin family of peptides have been the most widely studied and are emphasized. It is concluded that regulation of pancreatic enzyme secretion is a primitive action of cholecystokinin and that the sensitivity of gallbladder muscle and gastric acid-secreting cells to these peptides evolved later, possibly in the ancestral lineage that led to the gnathostomes. The need for increased digestive efficiency to support the higher levels of activity made possible by the evolution of jaws is suggested as a strong selection pressure leading to this pattern of evolution of endocrine regulation of gastrointestinal function.
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