Busija DW, Leffler CW. Exogenous norepinephrine constricts cerebral arterioles via alpha 2-adrenoceptors in newborn pigs.
J Cereb Blood Flow Metab 1987;
7:184-8. [PMID:
3031091 DOI:
10.1038/jcbfm.1987.42]
[Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The purpose of this study was to determine whether exogenous norepinephrine mediates cerebrovascular constriction via alpha 1- or alpha 2-adrenoceptors in anesthetized neonatal pigs. Diameters of pial arterioles in anesthetized piglets, 1--6 days old, were investigated using a "closed" cranial window. We examined constrictor effects of norepinephrine on pial arterioles in the absence and presence of relatively selective alpha 1-(prazosin) and alpha 2-(yohimbine) adrenoceptor antagonists (1 mg/kg i.v.). Yohimbine and prazosin inhibited pial arteriolar constriction induced by topical application of clonidine and phenylephrine (10(-6) and 10(-4) M, respectively), and yohimbine did not affect the response to topical phenylephrine. In one group diameter was 188 +/- 13 (mean +/- SEM) micron during control and 146 +/- 12 micron during 10(-5) M norepinephrine (22 +/- 5% constriction). Following yohimbine the same vessels did not constrict significantly. In another group 10(-5) M norepinephrine constricted arterioles by 22 +/- 5%, and this response was unaffected by prazosin (24 +/- 5% constriction). We conclude that pial arterioles are responsive to both alpha 1- and alpha 2-adrenoceptor agonists, that intravenous administration of prazosin and yohimbine results in these drugs crossing the blood-brain barrier and inhibiting constrictor effects of agonists, and that norepinephrine constricts pial arterioles predominantly via alpha 2-adrenoceptors.
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