CONTROVERSIES IN CARDIOVASCULAR RESEARCH* Do Vasomotor Nerves Significantly Regulate Cerebral Blood Flow?f
نویسنده
چکیده
IT IS worthwhile noting at the outset that this controversy is not new, the topic having been debated with vigor for the past 100 years or so. What has changed is the way in which the question at issue has been posed. In earlier experiments, the question was whether or not vasomotor nerves existed; but once they had been demonstrated, the problem was to assign a functional role to them. By the end of the 1930's, during which the action of vasomotor nerves and various drugs on pial vessels had been studied intensively, this question still was far from being resolved. On the one hand, it was clear that there were vasomotor nerves, and it was equally clear that section or stimulation of these nerves could markedly affect the caliber of pial vessels. On the other hand, the responses of pial vessels to such disturbances as hypoxia, hypercapnia, and hypotension were similar whether the nervous pathways were intact or not. Hence it was concluded that vasomotor nerves played little part in the regulation of cerebral vessels; the more important factors were intrinsic to the vascular bed. In the intervening years, extensive research has, if anything, sharpened the controversy. On the one hand, morphological and histological studies have shown that, in virtually every respect, the density of the adrenergic and cholinergic plexus on cerebral blood vessels and the appearance of the terminals at the neuromuscular junction are identical to those in other vascular beds. Pharmacological studies have identified adrenergic constrictor and cholinergic dilator receptors on smooth muscle, and experiments in which cerebral blood flow has been measured quantitatively have in most cases confirmed the earlier actions of vasomotor nerves. On
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تاریخ انتشار 2005