A Pharmacological Analysis of the Responses to Transmural Stimulation in Isolated Intestinal Preparations

nineteenth century by Langley (1898) and by Bayliss & Starling (1899), and has since been reported at intervals (for example, Auer & Meltzer, 1907; Veach, 1925 ; McSwiney & Wadge, 1928; Harrison & McSwiney, 1936; Martinson & Muren, 1960, 1963; Paton & Vane, 1963; Campbell, 1966a).Harrison & McSwiney (1936) suggested that the inhibitory responses they recorded were caused by adrenergic fibres in the vagus nerves, and this view was tentatively supported by Greeff, Kasperat & Osswald (1962) and by Paton & Vane (1963).Recent studies, however, both in whole animals (Martinson & Muren, 1963;Martinson, 1964Martinson, , 1965) and in isolated intestinal preparations (Burnstock, Campbell & Rand, 1966; Bennett, Burnstock & Holman, 1966; Campbell, 1966a) do not support this hypothesis.Thus the inhibitory responses to transmural stimulation in the taenia coil persisted in the presence of guanethidine or bretylium in concentrations which abolished the effects of sympathetic stimulation (Burnstock, Campbell & Rand, 1966).Moreover, the electro- physiological studies of Bennett, Burnstock & Holman (1966) on the taenia suggest that the inhibitory responses to sympathetic and to transmural stimulation are mediated by different sets of nerves.Recently, Holman & Hughes (1965) have obtained biphasic responses consisting of inhibitory and motor components after transmural stimulation of isolated intestinal preparations taken from mice, rats, guinea-pigs and rabbits.We have obtained similar responses in isolated intestinal preparations taken from rabbits and kittens, and have attempted a pharmacological analysis of the components of the response.In most experiments we have used the isolated ileum of the rabbit because its responses to sympathetic stimulation and its susceptibility to blocking drugs have been well character- ized, and the preparation shows regular activity for many hours.A preliminary account of some of this work has already been published (Day & Warren, 1967).