The Sympathetic Nervous System Is Involved in the Maintenance but Not Initiation of the Hypertension Induced by N ω -Nitro- l -Arginine Methyl Ester

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Abstract
Studies in anesthetized animals have advanced the theory that there is an important neurogenic component to the hypertension caused by pharmacological inhibition of nitric oxide, but studies in conscious animals have produced conflicting evidence for and against this theory. To try to reconcile the seemingly contradictory data, we hypothesized that the neurogenic component of this hypertension is time dependent such that the sympathetic nervous system is involved primarily in the maintenance, rather than the initiation, of the hypertension. We measured intra-arterial pressure in conscious, unrestrained rats with and without guanethidine-induced sympathectomy during varying durations of intravenous Nω-nitro-l-arginine methyl ester (L-NAME). The major new finding is that sympathectomy had no effect on the hypertensive response to bolus injections of L-NAME but in the same rats it produced a greater than 50% attenuation in the hypertension seen after 6 days of continuous L-NAME (change in mean arter...