Comparative effects of acetylcholine on the reptilian and mammalian aortae.
Responses of the lizard and the rabbit thoracic aortae to acetylcholine were studied. Acetylcholine (ACh) (10 nM-100 microM), carbachol (10 nM-50 microM) and PGF2 alpha (100 nM-100 microM) produced concentration-dependent contractions of the lizard thoracic aorta (LTA) with rapid tachyphylaxis. On the other hand, acetylcholine and carbachol relaxed the rabbit thoracic aorta (RTA) dose-dependently. There was no tachyphylaxis. Tachyphylaxis in the LTA was prevented by indomethacin (1 microM) or by rubbing the endothelium. Endothelial removal abolished ACh-induced relaxation of the RTA. Relaxation of the RTA and contractions of LTA were blocked by atropine, pirenzepine, acetoxy-N-methyl-piperidine methbromide (4-DAMP) and diltiazem. Removal of the endothelium rendered RTA insensitive to ACh. However, ACh-induced contractions of the LTA were not so influenced by removal of endothelial cells. It is concluded that the lizard thoracic aorta releases a metabolite of arachidonic acid that mediates tachyphylaxis. Relaxation of the RTA after ACh is mediated via the release of endothelium-dependent relaxing factor.
Ogundahunsi
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OA
Department of Pharmacology, Obafemi Awolowo College of Health Sciences, Ogun State University Teaching Hospital, Sagamu, Nigeria.
Tayo
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FM
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D015237:Dinoprost; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008116:Lizards / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D011460:Prostaglandins F / Q000494:pharmacology; D011817:Rabbits; D013045:Species Specificity
D002121:Calcium Channel Blockers; D011460:Prostaglandins F; D002217:Carbachol; D015237:Dinoprost; D000109:Acetylcholine; D007213:Indomethacin