Nitric Oxide and Vasoactive Intestinal Peptide as Dual Mediators of Neurogenic Relaxation in the Sheep Middle Cerebral Artery
In the cerebral circulation, large arteries are thought to contribute significantly to total vascular resistance. The physiological regulation of these blood vessels has a neural component (1). The identification of the neurotransmitter mechanisms will allow a greater understanding of how the distribution of cerebral blood flow is controlled. Although it is over 60 years since cerebral arteries were shown receive a vasodilator innervation (reviewed in 8), the transmitter candidate(s) remains a source of controversy. In 1975, Lee et al (5) demonstrated in the cat that the response was non-adrenergic and non-cholinergic in nature. In recent years, evidence has accumulated from studies on cerebral arteries implicating nitric oxide (NO) as the mediator of neurogenic vasodilation (2,3).However, NO is highly diffusible through membranes and therefore could not be stored in vesicles or released in a directional manner like classical transmitters. One possibility is that following stimulation, another substance present in nerves may activate NO synthase to produce NO.
KeywordsVasoactive Intestinal Peptide Cerebral Circulation Electrical Field Stimulation Classical Transmitter Neurogenic Response
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