[Neuro-hormonal regulation of the function of the enterocyte]

The intestinal epithelial cell, or enterocyte, performs a dual function: absorption and secretion. Absorption takes place in the villi and secretion in the crypts (and perhaps also in the villi). Both functions are controlled by complex extra- and intracellular systems. The extracellular system is mediated by neuromediators released in the subcellular space. Some mediators, like the vasoactive intestinal peptide (VIP) or the prostaglandins, stimulate secretion while others, like enkephalins, stimulate absorption. All these mediators act on intracellular metabolic processes by activating "second messengers" (e.g. amp or intracellular calcium) which in turn regulate the enterocyte transport system. Diarrheogenic processes are frequently due to disturbances in enterocyte control with abnormal stimulation of the secretory processes. Some pancreatic cancers and sympathicoblastomas release VIP into the blood stream in sufficient amounts to stimulate cAMP production by the enterocytes and, consequently, secretion. The cholera toxin and the E-coli thermolabile toxin can also induce stimulation of intracellular cAMP production. Conversely, the most promising antidiarrhoeal drugs are antisecretory agents, like opiates, which stimulate the enterocyte absorption processes.