Neuro Hormonal Control of Intestinal Transport

Abstract

An extremely complex picture is emerging of factors which influence intestinal transport and it is likely that final control is dependent on the complicated interplay of a variety of agents which influence the transporting epithelium. While a clear division between hormonal and neurological chemical messengers was originally discerned it is now clear that the division between these is becoming somewhat indistinct and artificial. The classical hormones, liberated from glands at a site removed from the point of action, such as thyroid, adrenal cortex and gonad are fairly clear-cut. However, the gut endocrine system made up of isolated cells in the gut mucosa specialised to produce one or more peptides not only subserves a hormonal role, by secreting their peptides into the bloodstream, but they also effect the local epithelial and sub-epithelial cells without recourse to the circulation. Such may be the case, for example, for gastrin, CCK, substance P and enteroglucagon. There has been an explosion of developments in the recognition of a variety of neurotransmitters other than the classical cholinergic and adrenergic agonists. Thus vasoactive intestinal peptide (VIP), substance P, serotonin, enkephalins and bombesin have been found in the enteric nervous system. Some nerves apparently contain more than one type of peptide. It is clear that some of these peptides are not restricted to nerves but some may also be found in paracrine cells. In addition, some of the neurotransmitters may escape into the bloodstream and subserve an endocrine role.