Evolution of Gastro-Entero-Pancreatic Endocrine Systems in Lower Vertebrates

Abstract

Although the title of this chapter uses the term endocrine, the division between the endocrine and nervous systems in vertebrates, particularly with regard to neurohormonal peptides, is now so small as to be virtually non- existent. For this reason it is impossible to consider the gut endocrine system in isolation, and necessarily this chapter will include, where relevant, due appreciation of neuronal peptides. In recent years increasing attention has been focussed upon the regulatory mechanisms in the vertebrate gut and their evolutionary interrelationships. The common feature which has emerged from these studies is that of the fundamental role of the peptide regulator. Peptide hormones have long been acknowledged to play an important part in gastrointestinal control mechanisms following the discovery of secretin over 80 years ago (Bayliss and Starling, 1903). Since this time, knowledge of gastro-entero-pancreatic (GEP) endocrine systems has evolved in a somewhat staccato fashion, bursts of activity frequently resulting from the appearance of new technical methods. The availability of immunochemical techniques has been a key development in recent years while currently, recombinant DNA technology has heralded a new era in GEP hormone research.