Vagal non-adrenergic inhibition of guinea-pig stomach

1. The effect of vagal and sympathetic stimulation on the mechanical and electrical activity (intracellular recording) of the body of the guinea-pig stomach was investigated in vitro.2. Following atropine, 1 x 10(-6)-1 x 10(-7) g/ml., vagal responses were reversed from excitatory to inhibitory.3. Sympathetic blockade, produced by alpha- and beta-receptor antagonists and adrenergic neurone-blocking agents, reduced or abolished sympathetic, but not vagal inhibition.4. Hexamethonium (5 x 10(-5) g/ml.) reduced vagal relaxation to 11-30% according to the stimulation rate. The residual response was maintained in the presence of 5-hydroxytryptamine tachyphylaxis.5. Many muscle cells were observed to be under the influence of both vagus and sympathetic nerves: the effect of sympathetic stimulation was always inhibitory in nature, but high stimulation rates were required. The effect of vagal stimulation was both excitatory and inhibitory even in the absence of atropine: low stimulation rates gave rise either to E.J.P.s (excitatory junctional potentials), often followed by spikes, or to I.J.P.s (inhibitory junctional potentials).6. In some spontaneously firing cells the interruption of electrical activity produced by vagal stimulation at 2/sec and sympathetic stimulation at 20/sec was recorded for a long enough time to check the effect of guanethedine (5 x 10(-6) g/ml.): the drug selectively blocked sympathetic inhibition.7. The significance of the inhibitory non-adrenergic transmitter, released by the intramural neurones activated by preganglionic vagal fibres, is discussed.