title: Pre-existing level of tone is an important determinant of cerebral artery autoregulatory responsiveness.
abstract: The objective of this study was to test the hypothesis that cerebral artery autoregulatory responses to increasing transmural pressure depend on the pre-existing level of vascular tone. Pial arteries were obtained from adult normotensive Wistar-Kyoto (WKY) rats, and were cannulated and studied under pressurized conditions using a video-assisted perfusion system. Myogenic tone developed spontaneously during equilibration, reducing the lumen diameter by 31% (n = 6). Each artery was then subjected to a series of step increases in transmural pressure of between 50 and 100 mmHg, a manoeuvre that produces autoregulatory constriction. Afterwards, serotonin was added to the perfusate to decrease lumen diameter by another 27% and the transmural pressure changes were repeated once more. The autoregulatory effectiveness in response to a change of 50----100 mmHg in transmural pressure was expressed as both the percentage change in diameter and the myogenic 'gain'. During the increased activation induced by serotonin, the autoregulatory responses to a change in transmural pressure were completely abolished; lumen diameter, which had previously decreased by 4.9 +/- 1.5%, increased by 10.5 +/- 4.5% (P less than 0.05). The nature of this change is further reflected in the myogenic gain, which was 0.39 +/- 0.14 in vessels with myogenic tone alone, and -1.14 +/- 0.56 for the same arteries at the higher level of activation (P less than 0.05). In additional experiments (n = 6), a comparable degree of constriction was induced with 0.5% ethanol, which increases calcium influx through receptor-independent mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)
authors: Department of Obstetrics and Gynecology, University of Vermont College of Medicine, Burlington 05405.
authors: G
authors: G
authors: Osol
authors: R
authors: R
authors: Osol
authors: W
authors: W
authors: Halpern
mesh_terms: D000818:Animals; D002536:Cerebral Arteries / Q000187:drug effects / Q000502:physiology*; D000431:Ethanol / Q000494:pharmacology; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology*; D009129:Muscle Tonus / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D011312:Pressure; D051381:Rats; D011921:Rats, Inbred WKY; D012701:Serotonin / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D012701:Serotonin; D000431:Ethanol