Abstract
Resistance blood vessels play an important role in maintenance of blood pressure and regulation of tissue blood flow (Mulvany and Aalkjaer, 1990). Resistance vascular tone is mainly controlled by sympathetic adrenergic nerves through the release of the neurotransmitter norepinephrine (Mulvany and Aalkjaer, 1990). Indeed, electrical field stimulation (EFS) of perivascular nerves in blood vessels isolated from various species evokes vasoconstriction, which is blocked by a-adrenoceptor antagonists (prazosin), adrenergic neuron blockers (guanethidine), and the neurotoxin tetrodotoxin (TTX). However, EFS of precontracted blood vessels isolated from various species causes vasodilation (Bevan and Bryden, 1987), which can be abolished by TTX but not by 13-adrenoceptor antagonists or muscarinic cholinoceptor antagonists (atropine). These results suggest nonadrenergic, noncholinergic (NANC) vasodilator innervation. However, these studies have been performed on relatively large arteries and/or conduit arteries in vitro, and evidence of NANC innervation and NANC neurotransmitter in small arteries and/or resistance arteries is scarce.
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