Effect of drugs and electrical field stimulation on circular muscle strips from human lower oesophagus

Sphincteric muscle from human lower oesophagus may be identifiable in vitro by its ability to develop a very high level of tone (sustained resting tension). Circular muscle strips from human lower oesophagus generally behave in a similar manner to strips from the opossum oesophagus with respect to development of tone, responses to electrical field stimulation and responses to a variety of drugs. Pharmacological analysis of responses to field stimulation in strips from the region of the oesophago-gastric junction suggests that the typical biphasic response (relaxation followed by an after-contraction) is mediated by nerves which are neither adrenergic nor cholinergic. Of the substances examined only vasoactive intestinal peptide (VIP) cannot be excluded as a possible candidate for the role of inhibitory transmitter. The mechanism producing the after-contraction is not clear but it would seem unlikely that this is simply a rebound contraction. The after-contraction can be blocked independently of the relaxation by a variety of agents and is potentiated by metoclopramide.