Biphasic effect of amethocaine on the rat stomach strip.

The biphasic effect of amethocaine on the rat stomach strip was studied. Lower concentrations of amethocaine contracted the rat stomach strip. At higher concentrations, there was an initial contraction followed by a relaxation. When the tissue was partially contracted with carbachol (200 ng ml(-1)), all concentrations of amethocaine used produced a relaxation. The relaxation was not reduced by phentolamine (5 X 10(-6) g ml(-1)) but was abolished by propanolol (5 X 10(-6) g ml(-1)) which also blocked adrenaline-induced relaxation of the preparation. Treatment of the tissue with 6-OHDA (250 microgram ml(-1)) did not abolish the relaxation. It is suggested that amethocaine may relax the rat stomach strip by an action similar to beta-adrenoreceptor stimulation. This action of amethocaine may be independent of endogenous catecholamines.