ABSTRACT
Vasopressin ([Arg(8)]vasopressin)-induced contraction was characterized using receptor agonists and antagonists for vasopressin and channel blockers in the rat basilar artery ring preparations. Vasopressin induced rhythmic contractions superimposed on a contraction in endothelium-intact preparations but not in denuded ones. Endothelium removal shifted the concentration-response curve for vasopressin leftward and upward. In endothelium-denuded preparations, vasopressin V(1) receptor antagonist shifted the concentration-response curve for vasopressin downward and rightward. Vasopressin V(1) receptor agonist caused contraction but V(2) receptor agonist did not. The contractile response to vasopressin was partly inhibited by nifedipine, SK&F 96365 (1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole) and niflumic acid. In the absence of extracellular Ca(2+), vasopressin produced a transient contraction. Charybdotoxin produced an upward and leftward shift of the concentration-response curve for vasopressin. These results suggest that vasopressin elicits contraction due to Ca(2+) influx through voltage-dependent and receptor-operated Ca(2+) channels and to Ca(2+) release from Ca(2+) stores by activating vasopressin V(1) receptors in the rat basilar artery.
Subject(s)
Basilar Artery/drug effects , Vasoconstriction/drug effects , Vasopressins/pharmacology , Animals , Antidiuretic Hormone Receptor Antagonists , Apamin/pharmacology , Basilar Artery/physiology , Calcium/pharmacology , Charybdotoxin/pharmacology , Dose-Response Relationship, Drug , Endothelium, Vascular/physiology , Imidazoles/pharmacology , In Vitro Techniques , Male , Potassium Chloride/pharmacology , Rats , Rats, Wistar , Receptors, Vasopressin/agonists , Vasodilation/drug effectsABSTRACT
The reaction of nucleotides with superoxide gave the corresponding nucleobases in good yield. The base-release reaction of nucleotides due to superoxide was examined and compared to that of nucleosides. Hence, the phosphate moiety greatly enhances the yields, in particular those of adenine from adenosine monophosphates. Superoxide in combination with the phosphate moiety has been revealed to be more active than superoxide alone. The phosphate peroxy radical, generated in situ from superoxide and phosphate, seems to be the species responsible for the formation of the free bases.
