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INHIBITION BY SUBSTANCE P OF SOME PERIPHERAL ACTIONS OF ACETYLCHOLINE IN THE CAT
Author(s) -
CLARK S.L.,
RYALL R.W.
Publication year - 1982
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1982.tb09259.x
Subject(s) - acetylcholine , substance p , peripheral , neuroscience , pharmacology , cats , medicine , chemistry , biology , neuropeptide , receptor
1 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. 2 Substance P (2–20 nmol) injected into the lingual artery giving estimated concentrations in arterial blood of 10 −6 to 10 −5 m , or intravenously giving estimated concentrations in blood of 10 −8 to 10 −7 m , reduced hexamethonium‐sensitive but not atropine‐sensitive responses. 3 The 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. 4 The 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. 5 The 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. 6 There was desensitization to all of these effects of substance P which probably contributed to the variation in the magnitude of the effects observed. 7 Substance P had no effect on muscarinic actions of acetyl‐β‐methylcholine on the nictitating membrane or blood pressure. 8 The 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.