To determine the effects of sympathetic denervation and dexamethasone on the individualcerebral vascular pressure profile during hypoxia, the authors measured the pial microvascular pres-sure in 24 anesthetized rabbits with a servo-null system. At a simulated altitude of 4000 meters, inthe intact group, the mean pressure in pial arterioles of 50-70 μm in diameter decreased markedly.The ratio of pressure drop between the upstream and downstream of the arteriole measured in-creased markedly, and the blood flow in the internal carotid artery was nearly doubled of the nor-mal. The pial arteriolar pressures of both the denervated and dexamethasone groups were significantlyhigher than that of the intact group, but were not different from their prehypoxic values. The ratioof pressure drop between the upstream and downstream of the denervated and dexamethasonegroups remained unchanged, and much lower than that of the intact group, These results lead tothe following conclusions: (1) Sympathetic nerves and dexamethasone exert no effect on thelongitudinal distribution of cerebro-vascular pressure in rabbits during normoxia, normocapnia andnormotension.(2) During hypoxia, pressure drop increases in the upstream arteries and/or decreasesin the downstream vessels of the microvascular pressure measured site (arterioles 50- 70 μm in diame-ter) partly due to the activation of the sympathetic nerve. (3) Dexamethasone can prevent theredistribution of cerebrovascular pressure induced by hypoxia, which can partly explained the ac-tion of dexamethasone in preventing high altitude sickness.
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