Effect of peripheral and central alpha-adrenoceptor blockade on cerebral microvascular and blood flow responses to hypoxia.
The purpose of this study was to evaluate the effects of vascular and central alpha-adrenoceptor blockade on cerebral blood flow (CBF) and utilization of brain arteriolar and capillary reserve in conscious rats during normoxia and hypoxia (8% O2 in N2). Animals were divided into three groups and administered either saline, N-methyl chlorpromazine (does not cross the blood-brain barrier), or phenoxybenzamine (crosses the blood-brain barrier) in equipotent doses. Neither agent affected regional CBF and the utilization of brain microvascular reserve during normoxia. CBF increased from 70.9 +/- 2.9 (SEM) ml/min/100 g in the control normoxic group to 123.8 +/- 4.2 ml/min/100 g in control hypoxic animals. In control, hypoxic flow to pons and medulla of the brain was higher than to cortex, hypothalamus or thalamus. The percent of arterioles/mm2 perfused increased from 49.6 +/- 2.0% during control normoxia to 65.6 +/- 3.0% during control hypoxia. The percentage of capillaries/mm2 perfused changed similarly. Hypoxic CBF was increased similarly after administration of N-methyl chlorpromazine or phenoxybenzamine. Administration of N-methyl chlorpromazine or phenoxybenzamine eliminated regional differences in hypoxic CBF and the utilization of arterioles, and did not affect capillary response. There was no difference between the effect of N-methyl chlorpromazine and phenoxybenzamine on cerebral microvascular and blood flow responses to hypoxia. It was concluded that peripheral alpha-adrenoceptors affect the distribution of regional microvascular and blood flow responses to hypoxia, and central alpha-adrenoceptors probably do not participate in this effect.
Kissen
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Department of Physiology and Biophysics University of Medicine and Dentistry of New Jersey Robert Wood Johnson Medical School, Piscataway 08854-5635.
Weiss
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D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000098:blood supply*; D006439:Hemodynamics / Q000187:drug effects; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D008833:Microcirculation; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*
D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha