The eupeptide system: A general theory of gastrointestinal hormones.

Increasing knowledge of gastrointestinal "hormones" suggests a system which differs in many, if not most, respects from other endocrine systems. The established model of endocrine function, derived from studies of the hormones regulating growth, metabolism, and sexual function, is inappropriate; attempts to apply concepts such as the importance of plasma-hormone concentrations to the digestive tract have met with limited success. A new model of the gastrointestinal polypeptide system is proposed in which local "paracrine" action may be no less important, or more important, than distant "endocrine" action, and in which modulation of integrated neural control is a major function. The application of the word "hormone" to this polypeptide system is a devaluation of the term and an obstacle to the design of relevant physiological studies; an alternative nomenclature is proposed.