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Neurogenic Vasoconstriction as Affected by Cholinergic and Nitroxidergic Nerves in Dog Ciliary and Ophthalmic Arteries

From the Department of Pharmacology, Shiga University of Medical Science, Ohtsu, Japan.

PURPOSE. To determine the involvement of noradrenergic and other vasoconstrictor nerves in the contraction of ocular arteries and the modification by cholinergic and nitroxidergic nerves of vasoconstrictor nerve function.

METHODS. Changes in isometric tension were recorded in helical strips of the canine posterior ciliary and external ophthalmic arteries denuded of the endothelium, which were stimulated by transmurally applied electrical pulses (5 Hz). Vasoconstrictor mediators were analyzed by pharmacological antagonists, such as prazosin, ,ß-methylene ATP, a P_2X-purinoceptor antagonist, and BIBP3226, a neuropeptide Y receptor antagonist.

RESULTS. Transmural electrical stimulation produced contractions that were potentiated by N^G-nitro-L-arginine (L-NA), a nitric oxide (NO) synthase inhibitor. The contraction was partially inhibited by prazosin and abolished by combined treatment with ,ß-methylene ATP but was not influenced by BIBP3226. Stimulation-induced contraction was attenuated by physostigmine and potentiated by atropine. Contractions induced by exogenous ATP were reversed to relaxations by ,ß-methylene ATP. In the strips treated with L-NA, prazosin, and ,ß-methylene ATP, the addition of L-arginine elicited relaxations by nerve stimulation. The ATP-induced relaxation was attenuated by aminophylline, whereas neurogenic relaxation was unaffected.

CONCLUSIONS. Ciliary and ophthalmic arterial contractions by nerve stimulation are mediated by norepinephrine and ATP, which stimulate ₁-adrenoceptor and P_2X purinoceptor, respectively. ATP from the nerve is unlikely involved in vasodilatation. Acetylcholine derived from the nerve impairs the neurogenic contraction, possibly by interfering with the release of vasoconstrictor transmitters, and neurogenic NO also inhibits the contraction postjunctionally by physiological antagonism.

This article has been cited by other articles:

				N. Toda and T. Okamura The Pharmacology of Nitric Oxide in the Peripheral Nervous System of Blood Vessels Pharmacol. Rev., June 1, 2003; 55(2): 271 - 324. [Abstract] [Full Text] [PDF]

				K. Ayajiki, T. Tanaka, T. Okamura, and N. Toda Evidence for nitroxidergic innervation in monkey ophthalmic arteries in vivo and in vitro Am J Physiol Heart Circ Physiol, October 1, 2000; 279(4): H2006 - H2012. [Abstract] [Full Text] [PDF]