Vasodepressor responses to [D-Ala2]-endomorphin 2 (TAPP) are mediated by an L-NAME-sensitive mechanism in the rat.
Endomorphin 1 and 2 are newly discovered endogenous ligands for the mu-opioid receptor. We recently showed that endomorphin 1 and 2 have vasodepressor activity, and in this study, responses to a novel endomorphin analog [D-Ala2]-endomorphin 2 (TAPP) were investigated in the systemic vascular bed of the rat. Intravenous injections of TAPP, endomorphin 1, and endomorphin 2 decreased systemic arterial pressure in a dose-related manner. Decreases in systemic arterial pressure in response to TAPP were similar to vasodepressor responses to endomorphin 1 and 2 and were not altered by passage of time. Decreases in systemic arterial pressure in response to TAPP, endomorphin 1, and endomorphin 2 were attenuated by the opioid receptor antagonist naloxone (2 mg/kg, i.v.) when the vasodepressor response to the ORL1-receptor agonist nociceptin (orphanin FQ) was not altered. Decreases in systemic arterial pressure in response to TAPP, endomorphin 1 and 2, and acetylcholine were attenuated by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME; 50 mg/kg, i.v.) when decreases in systemic arterial pressure in response to nociceptin and calcitonin gene-related peptide (CGRP) were not altered. These results indicate that TAPP, endomorphin 1, and endomorphin 2 decrease systemic arterial pressure by a naloxone-sensitive mechanism and suggest that the vasodepressor response to TAPP, endomorphin 1 and 2, but not nociceptin, is mediated by the release of nitric oxide.
Department of Pharmacology, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA.
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Champion
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Kadowitz
D000578:Amidines / Q000494:pharmacology*; D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D015740:Calcitonin Gene-Related Peptide / Q000187:drug effects / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology; D018847:Opioid Peptides / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013008:Somatotypes / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects; D000097629:Nociceptin
D000578:Amidines; D015740:Calcitonin Gene-Related Peptide; D019331:NG-Nitroarginine Methyl Ester; D009270:Naloxone; D009292:Narcotic Antagonists; D018847:Opioid Peptides; D000097629:Nociceptin; C034807:tetra-4-amidinophenoxypropane