Artikel
Evidence for upregulation of endothelin(B) receptors in the cerebrovasculature following transient ischemia in the rat
Verstärkte Expression von Endothelin(B)-Rezeptoren in Hirngefäßen der Ratte nach transienter Ischämie
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Autoren
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G. Koch
- Institut für Neurochirurgische Forschung, Neurochirurgische Klinik, Klinikum der Stadt Mannheim, Universität Heidelberg, Mannheim
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N. Weinzierl
- Institut für Neurochirurgische Forschung, Neurochirurgische Klinik, Klinikum der Stadt Mannheim, Universität Heidelberg, Mannheim
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R. Erber
- Institut für Neurochirurgische Forschung, Neurochirurgische Klinik, Klinikum der Stadt Mannheim, Universität Heidelberg, Mannheim
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Lothar Schilling
- Institut für Neurochirurgische Forschung, Neurochirurgische Klinik, Klinikum der Stadt Mannheim, Universität Heidelberg, Mannheim
| Veröffentlicht: | 23. April 2004 |
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Gliederung
Text
Objective
To study changes of receptor expression and function in cerebral arteries after transient focal ischemia in rats. The focus was on the components of the endothelin (ET) system.
Methods
In male Sprague Dawley rats a 2 h focal ischemia was induced by intraluminal occlusion of the right middle cerebral artery (MCA) followed by 46 h of reperfusion. At the end of the experiment the animals were killed and the brains removed. In functional studies both MCAs were isolated and transferred into organ baths for measurement of isometric force. Tests of vasomotor stimuli included: (i) depolarisation-induced contraction (reference contraction), (ii) endothelium-dependent relaxation upon bradykinin (Bk), (iii) endothelium-dependent relaxation upon sarafotoxin 6c (S6c, a selective ETB receptor agonist), (iv) contraction upon ET-1 (ETA and ETB receptor agonist), (v) contraction upon S6c in the absence and presence of nitro-L-arginine (L-NNA) to inhibit nitric oxide synthetase. In gene expression studies both MCAs and branching arteries were isolated and total mRNA extracted. Reverse transcription (rt) was performed followed by polymerase chain reaction (PCR) using specific primers for the following genes: ET-1, ET(A) and ET(B) receptors, and ET converting enzyme (ECE).
Results
In the MCA taken from the ischemic side (i) stimulation of ET(B) receptors by S6c yielded significantly enhanced relaxation, (ii) stimulation of ET(A) receptors by ET-1 following ET(B) receptor desensitisation yielded significantly enhanced contraction, (iii) stimulation of ET(B) receptors by S6c resulted in contraction only in the presence of L-NNA, and (iv) after MCAO the relative levels of mRNA (compared to GAPDH as the housekeeping gene) were increased for ET(B) mRNA (x 3.2; p<0.05 vs. control) and ECE mRNA (x 1.8), but nor for ET(A) and ET-1 mRNA.
Conclusions
The functional studies suggest an upregulation of the relaxation-inducing ET(B1) and a de-novo expression of a contraction-inducing ET(B2) receptor in cerebral arteries. These alterations are reflected by an increased expression of the ET(B) mRNA on the side of ischemia. In contrast, there were no alterations of the expression of ET(A) mRNA suggesting that the enhanced contraction observed after stimulation of the ET(A) receptor is due to alterations in the second messenger cascade.
