Effect of peripheral and central alpha-adrenoceptor blockade on cerebral microvascular and blood flow responses to hypoxia.

Abstract

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.

• Authors: I Kissen, H R Weiss
• Journal: Life sciences (Life Sci) Vol. 48 Issue 14 Pg. 1351-63 ( 1991) ISSN: 0024-3205 [Print] Netherlands
• PMID: 1672555 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Adrenergic alpha-Antagonists
• Receptors, Adrenergic, alpha

Topics

• Adrenergic alpha-Antagonists (pharmacology)
• Animals
• Brain (blood supply)
• Hemodynamics (drug effects)
• Hypoxia (physiopathology)
• Male
• Microcirculation
• Rats
• Receptors, Adrenergic, alpha (physiology)