Preliminary study of the vasorelaxant effects of (+)-nantenine, an alkaloid isolated from Platycapnos spicata, in rat aorta.
In this work, the potential vasorelaxant activity of (+)-nantenine, an alkaloid isolated from Platycapnos spicata, was studied for the first time in rat aorta. (+)-Nantenine (3 - 30 microM) totally relaxed, in a concentration-dependent manner and with almost equal effectiveness, the contractions induced by noradrenaline (NA) or by a high KCl concentration (60 mM) in intact rat aortic rings. Mechanical removal of endothelium and/or pretreatment of aorta rings with glibenclamide (10 microM) or tetraethylammonium (TEA, 2 mM) did not significantly modify the vasorelaxant effects of this aporphine alkaloid. In the experiments in Ca(2+)-free medium, (+)-nantenine (10 microM) had no effect on caffeine-induced contractions. Furthermore, in the studies with radiolabelled Ca(2+), (+)-nantenine (3 - 30 microM) did not modify the basal uptake of (45)Ca(2+) but decreased, in a concentration-dependent fashion, the influx of (45)Ca(2+) induced by NA and KCl in endothelium-containing and endothelium-denuded rat aortic rings. In addition, (+)-nantenine (3 - 30 microM) was ineffective to scavenge superoxide anion (O(2) (-)) radicals generated by the hypoxanthine (HX)-xanthine oxidase (XO) system and/or to inhibit XO activity. These results indicate that: a) the vasorelaxant effects of (+)-nantenine in rat aorta are due, at least in part, to a blockage of Ca(2+) influx through transmembrane calcium channels, b) the activation of ATP-sensitive K(+) channels (K(ATP)) and large conductance Ca(2+)-activated K(+) channels (K(Ca)) present in smooth muscle cells, the presence (integrity) of endothelial system, an inhibitory action on XO enzymatic activity and/or O(2)(-) radicals scavenging properties are not involved in the vascular effects of (+)-nantenine in rat aorta described above.
Orallo
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F
Departamento de Farmacología, Facultad de Farmacia, Universidad de Santiago de Compostela, Spain. fforallo@usc.es
Alzueta
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AF
D000818:Animals; D001011:Aorta / Q000187:drug effects* / Q000502:physiology; D001060:Aporphines / Q000737:chemistry / Q000494:pharmacology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D028101:Papaveraceae; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013481:Superoxides / Q000378:metabolism; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology*; D014969:Xanthine Oxidase / Q000378:metabolism
D001060:Aporphines; D002121:Calcium Channel Blockers; D010936:Plant Extracts; D014665:Vasodilator Agents; D013481:Superoxides; D002110:Caffeine; D014969:Xanthine Oxidase; D002118:Calcium; C041615:nantenine