Inhibition by Substance P of Some Peripheral Actions of Acetylcholine in the Cat
The effect of substance P on contractions of the nictitating membrane and pressor responses to acetylcholine (ACh) and dimethylphenyl-piperazinium (DMPP) which were mediated via nocotinic receptors was studied in cats anaesthetized with chloralose. 2Substance P (2â€“20 nmol) injected into the lingual artery giving estimated concentrations in arterial blood of 10âˆ’6 to 10âˆ’5 m, or intravenously giving estimated concentrations in blood of 10âˆ’8 to 10âˆ’7 m, reduced hexamethonium-sensitive but not atropine-sensitive responses. 3The pressor effects of ACh and DMPP injected intra-arterially in atropinized and non-atropinized cats respectively were consistently attenuated by substance P given intra-arterially or intravenously. 4The contractile effect of ACh in atropinized and of DMPP in non-atropinized cats was attenuated by substance P injected intra-arterially but only rarely when the polypeptide was injected intravenously. 5The depressor effects of substance P per se were variable in magnitude and duration as were the inhibitory effects upon nicotinic receptors. The depressor and inhibitory effects of substance P were unrelated. 6There was desensitization to all of these effects of substance P which probably contributed to the variation in the magnitude of the effects observed. 7Substance P had no effect on muscarinic actions of acetyl-Î²-methylcholine on the nictitating membrane or blood pressure. 8The results are discussed in relation to the ubiquity of the modulatory actions of substance P on nicotinic receptors and in relation to the possible physiological significance of the action.
S. L. Clark and R. W. Ryall, "Inhibition by Substance P of Some Peripheral Actions of Acetylcholine in the Cat," British Journal of Pharmacology, British Pharmacological Society, Jan 1982.
The definitive version is available at https://doi.org/10.1111/j.1476-5381.1982.tb09259.x
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