Evidence that the contractile response of the guinea-pig ileum to capsaicin is due to substance P release.
The mechanism of action of capsaicin on the guinea-pig isolated ileum was studied. Capsaicin (1.5 x 10(-6) mol 1(-1) produced a large contractile response of the ileum which exhibited marked tachyphylaxis. The response was reduced by treatment of preparations with atropine, 5 x 10(-6) mol 1(-1), and by substance P-autodesensitization, and was abolished by a combination of these treatments. It was concluded that capsaicin released both substance P and acetylcholine from the guinea-pig ileum. Evidence for a cholinergic component in the action of high concentrations of substance P was also obtained and therefore it is proposed that capsaicin releases substance P from neurones in the ileum, and the released substance P in turn stimulates cholinergic neurones to release acetylcholine, as well as producing direct muscle contraction.
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002211:Capsaicin / Q000494:pharmacology*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D010830:Physostigmine / Q000494:pharmacology; D013373:Substance P / Q000378:metabolism*
D005231:Fatty Acids, Unsaturated; D013373:Substance P; D001285:Atropine; D010830:Physostigmine; D000109:Acetylcholine; D002211:Capsaicin