© 1999 by European Society of Cardiology
Copyright © 1999, European Society of Cardiology
NOS inhibition potentiates norepinephrine but not sympathetic nerve-mediated co-transmission in resistance arteries
Autonomic Physiology Unit and Clinical Research Initiative in Heart Failure, Division of Neuroscience & Biomedical Systems, Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Scotland, UK
* Corresponding author. Tel.: +44-141-330-3187; fax: +44-141-337-1651. joyce.macmillan{at}bio.gla.ac.uk
Objective: The in vitro interaction between sympathetic nerves and basal nitric oxide release was studied in a resistance artery, since these interact powerfully in large vessels. Methods: The pharmacological interaction between L-NAME and vasoconstriction to field stimulation of sympathetic nerves or exogenous norepinephrine was studied in rabbit cutaneous resistance arteries in wire myographs. Results: Relaxation of norepinephrine-induced tone by acetylcholine, but not sodium nitroprusside, was blocked by N
-nitro-L-arginine methyl ester (L-NAME: 100 µM), indicating that the agonist-induced release of nitric oxide could oppose the vasoconstrictor effect of norepinephrine and confirming that L-NAME had no effect on endothelium-independent vasodilatation. L-NAME increased norepinephrine potency indicating basal NO release. With short bursts of electrical field stimulation purinergic transmission was dominant at low frequencies and adrenergic at high frequencies. L-NAME had no effect on nerve-mediated responses, even after blocking the purinergic component with 
,β-methylene ATP (3 µM), suggesting that the influence of spontaneously released nitric oxide does not extend to the vascular smooth muscle cells under adrenergic nervous control. Conclusion(s): This resistance artery exhibits a highly effective nitric oxide-mediated vasodilatation to acetylcholine. It has basal release of nitric oxide which antagonises exogenous norepinephrine. However, basal nitric oxide did not influence adrenergic nerve transmission, which contrasts with previous studies of larger arteries and veins. We speculate that in small resistance arteries there may be a spatial limitation to the zones of vascular smooth muscle influenced by the adrenergic nerves and by basal nitric oxide from the endothelium, respectively. The role of endogenous nitric oxide in modulating vascular tone may thus be less in resistance arteries than in conducting arteries or capacitance vessels and purinergic transmission appears to be particularly resistant.
KEYWORDS Acetylcholine; Adrenergic; Autonomic nervous system; Nitric oxide; N-nitro-L-arginine methyl ester; Rabbit
1 Present address: Department of Physiology and Pharmacology, University of Strathclyde, Royal College, 204 George St., Glasgow G1 1XW.
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