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A comparison of the excitatory and inhibitory effects of non‐adrenergic, non‐cholinergic nerve stimulation and exogenously applied ATP on a variety of smooth muscle preparations from different vertebrate species

1 . The responses to non‐adrenergic, non‐cholinergic nerve stimulation have been compared with those to exogenously applied ATP on seventeen different tissues from a number of vertebrate classes. 2 . Stimulation of all the mammalian gut preparations studied (with the exception of the guinea‐pig ileum) after blockade of the effects of adrenergic and cholinergic nerve stimulation by guanethidine (3·5 μm) and hyoscine (1–3 μm) caused inhibition; exogenously applied ATP mimicked this inhibitory response. 3 . Stimulation of the guinea‐pig ileum in the presence of hyoscine and guanethidine, usually caused a diphasic response, relaxation followed by contraction; exogenously applied ATP mimicked this response, in contrast to acetylcholine and noradrenaline which caused excitation and relaxation respectively. 4 . Stimulation of preparations of lower vertebrate gut and guinea‐pig bladder in the presence of hyoscine and guanethidine caused contraction; exogenously applied ATP mimicked this contractile response. 5 . In each preparation the time course of the response to ATP was similar or identical to the response to non‐adrenergic, non‐cholinergic nerve stimulation. 6 . The results are consistent with the hypothesis that a purine nucleotide may be the transmitter substance released from non‐adrenergic, non‐cholinergic nerves supplying smooth muscle preparations from a number of vertebrate classes.