Role of sympathetic nerve activity in the generation of vascular nitric oxide in urethane-anesthetized rats. Hypertension

The aim of the present study was to examine the involvement of the sympathetic nervous system in the generation or release of vascular nitric oxide. In urethane-anesthetized rats, the administration of the novel nitric oxide synthesis inhibitor L-jV-nitro arginine (LNA) (0.02 mmol/kg i.v.) increased mean arterial pressure and renal, mesenteric, and hindquarter vascular resistances. The intravenous administration of L-arginine (60 nig/kg plus 12 mg/kg/ min i.v.) produced small reductions in arterial pressure and vascular resistances and abolished the hemodynamic effects of LNA. Pretreatment with the ganglion blocking agent chlorison-damine lowered mean arterial pressure and vascular resistances, abolished the LNA-induced pressor and renal vasoconstrictor response, and attenuated the increases in mesenteric and hindquarter resistances. In contrast, the vasodilator hydralazine lowered mean arterial pressure and vascular resistances to levels equivalent to that of ganglionic blockade; however, the subsequent administration of LNA still produced significant increases in arterial pressure and regional vascular resistances. In ganglion-blocked rats in which pressure and vascular resistances were returned to normal levels by infusion of arginine vasopressin or phenyleph-rine, the pressor and vasoconstrictor effects of LNA were restored. However, phenylephrine wa