Differential effects of nitroblue tetrazolium on the hemodynamic responses elicited by activation of α1-adrenoceptors and 5-HT2 receptors in conscious rats

This study determined the effects of the lipophobic electron acceptor, nitroblue tetrazolium (5 μmol/kg, i.v.) on the vasoconstrictor responses elicited by the 5-hydroxytryptamine2 (5-HT2) receptor agonist, α-methyl-5-HT (5-50 μg/kg, i.v.) and the α1-adrenoceptor agonist, phenylephrine (2.5-20 μg/kg, i.v.) in conscious Sprague-Dawley rats. The systemic injection of nitroblue tetrazolium elicited pronounced hemodynamic responses that subsided by 10-15 min. Prior to the administration of nitroblue tetrazolium, the injections of α-methyl-5-HT and phenylephrine elicited dose-dependent increases in mean arterial blood pressure and mesenteric, renal and hindquarter vascular resistances. After administration of nitroblue tetrazolium, the vasoconstrictor responses elicited by α-methyl-5-HT were augmented whereas those elicited by phenylephrine were diminished. These results are consistent with the possibility that nitroblue tetrazolium interacts with the extracellular ligand-binding domains of 5-HT2 receptors and α1-adrenoceptor and that this interaction has opposite effects on activities of these G protein coupled receptors.