Enkephalins and enkephalinase inhibitors in intestinal fluid and electrolyte transport.

Opioids have long been known to inhibit intestinal fluid and electrolyte secretion. They act locally on central and peripheral opiate receptors where they are rapidly degraded by neuropeptidases, the major one being enkephalinase (EC 3.4.24.11). A number of studies have shown that, when the problem of degradation can be overcome, enkephalins have potent antisecretory properties. In 1980, an enkephalinase inhibitor was described which increased the functional availability of enkephalins. More recently an orally active enkephalinase inhibitor, acetorphan, has been shown to inhibit infectious and chemically induced diarrhoea. Acetorphan does not appear to affect gastrointestinal motility and, although it also inhibits the breakdown of a range of other neuropeptides, such as substance P and neuropeptide Y, it is a promising agent with therapeutic potential.