Endothelin B receptor-deficient rats as a subtraction model to study the cerebral endothelin system

doi:10.1016/S0306-4522(98)00663-0

Neuroscience

Volume 91, Issue 3, July 1999, Pages 1067-1075

https://doi.org/10.1016/S0306-4522(98)00663-0 Get rights and content

Abstract

Endothelins, due to their potent vasoactivity and mitogenicity, appear to play an important role in the brain, where all components of the endothelin system, peptides, receptors and converting enzyme, are expressed. To further elucidate the role of the cerebral endothelin system, astrocytes and cerebral vessels from sl/sl rats, devoid of functional endothelin B receptors, have been employed. Astrocytes from sl/sl rats display the following abnormalities as compared to wild-type (+/+) cells: (i) elevated basal extracellular endothelin-1 levels; (ii) exclusive presence of functional endothelin A receptors; (iii) increased extracellular endothelin-1 levels upon endothelin A receptor blockade; (iv) augmented basal endothelin-converting enzyme activity; (v) altered calcium response to endothelin-1. The basilar artery of sl/sl rats shows an enhanced constricting response to endothelin-1 and fails to dilate in response to endothelin-3, shifting the endothelin vasomotor balance to constriction.

In conclusion, endothelin B receptors may be essential for restricting extracellular endothelin-1 levels in the brain, as well as for a balanced cerebral vasomotor action of endothelins.

Section snippets

Rats

For all experiments, animals from the Wistar–Imamichi AR strain (congenital aganglionosis rat) were used.18., 30. These rats have an autosomal recessive 301-bp deletion in the ET_B gene, spanning exon 1 and intron 1, corresponding to the first and second transmembrane domains of the ET_B receptor.¹¹ The animals were bred in our laboratory by mating of heterozygous sl/+ rats. The genotype of each animal used for experiments was confirmed by polymerase chain reaction (PCR) amplification of genomic

Immunoreactive endothelin-1 concentrations in the supernatant of cortical astrocyte cultures: effect of selective endothelin A and B receptor antagonists (Fig. 1A)

There were no differences regarding growth of cells from either genotype in culture. In both sl/sl and +/+ cultures, immunoreactive (IR) ET-1 concentrations increased gradually over time. Basal levels of extracellular ET-1 were significantly (P<0.01) higher in ET_B-deficient as compared to wild-type cultures, reaching 356% (range: 238–577%) of the IR ET-1 concentration of the latter at the 48-h time-point. In accordance with our previous findings in astrocyte cultures of Wistar rats,¹⁶ addition

Discussion

The employment of ET_B-deficient rats as a subtraction model can serve two tasks: (i) exploration of the physiological role of the ET_B and of the ET_A receptor; (ii) recognition of functional/morphological consequences of ET_B deficiency, which occurs not only upon genetic lack of functional ET_B receptors, but also upon pathophysiological down-regulation.

We have shown that lack of ET_B receptors leads to measurable functional consequences in astrocytes and cerebral arteries. In ET_B deficiency,

Conclusion

Intact ET_B receptors in the CNS appear to play an important role, even under basal conditions, in the control of extracellular ET-1 levels and in counterbalancing ET_A-mediated vasoconstriction, thereby protecting against ischemia. ET_B-deficient rats are a suitable model to study the role of endothelin receptors within the cerebral endothelin system. This model may prove particularly helpful for understanding, and perhaps treating, the consequences of ET_B down-regulation as observed in the

Acknowledgements

This work was sponsored by grants from the DFG (Eh133/1-2,3) and from Knoll AG, Ludwigshafen, Germany. A.-L.S. was supported by the Alexander-von-Humboldt Foundation.

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Alzheimer's disease (AD) is a progressive brain disorder leading to impairment of learning and memory. Amyloid β (Aβ) induced oxidative stress has been implicated in the initiation and progression of AD. Endothelin (ET) and its receptors have been considered as therapeutic targets for AD. Recent studies indicate that stimulation of ET_B receptors may provide neuroprotection. The purpose of this study was to determine the preventative effect of selectively stimulating ET_B receptors on cognitive impairment and oxidative stress in Aβ treated non-diabetic and diabetic (induced by streptozotocin) rats. Rats were concurrently treated with Aβ_1–40 (day 1, 7 and 14) and either saline, IRL-1620 (an ET_B agonist), and/or BQ788 (an ET_B antagonist) daily for 14 days in the lateral cerebral ventricles using sterotaxically implanted cannula; experiments were performed on day 15. Aβ treatment produced a significant (p < 0.0001) increase of 360% and 365% in malondialdehyde levels (a marker of lipid peroxidation) in non-diabetic and diabetic rats, respectively, compared to sham group. Antioxidants (superoxide dismutase and reduced glutathione) decreased following Aβ treatment compared to sham group. Treatment with IRL-1620 reversed these effects, indicating that ET_B receptor stimulation reduces oxidative stress injury following Aβ treatment. In Morris swim task, Aβ treated rats showed impairment in spatial memory. Rats treated with IRL-1620 significantly reduced the cognitive impairment induced by Aβ. BQ788 treatment completely blocked IRL-1620 induced reduction in oxidative stress and cognitive impairment. Results of the present study demonstrate that IRL-1620 improved both acquisition (learning) and retention (memory) on water maze task and reduced oxidative stress parameters. It can be speculated that ET_B receptor stimulation prevents cognitive impairment and may be useful in neurodegenerative diseases.
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Endothelin B receptor-deficient rats as a subtraction model to study the cerebral endothelin system

Abstract

Section snippets

Rats

Immunoreactive endothelin-1 concentrations in the supernatant of cortical astrocyte cultures: effect of selective endothelin A and B receptor antagonists (Fig. 1A)

Discussion

Conclusion

Acknowledgements

Life Sci.

Eur. J. Pharmac.

Brain Res.

Brain Res.

Life Sci.

J. biol. Chem.

Brain Res.

Biochem. biophys. Res. Commun.

Prog. Neurobiol.

Fedn Eur. biochem. Socs Lett.

Analyt. Biochem.

Expl Neurol.

Biochem. biophys. Res. Commun.

Biochem. biophys. Res. Commun.

Trends pharmac. Sci.

Endothelin binding to NG108-15 cells: evidence for conventional ETA and ETB receptor subtypes and super-high affinity binding components

Cell. molec. Biol.

The endothelin system and endothelin-converting enzyme in the brain: molecular and cellular studies

Neurochem. Res.

Growth factor activity of endothelin-1 in primary astrocytes mediated by adhesion-dependent and -independent pathways

J. Neurosci.

Interstitial deletion of the endothelin-B receptor gene in the spotting lethal (sl) rat

Hum. molec. Genet.

Endothelin-induced contraction and relaxation of rat isolated basilar artery: effect of BQ-123

J. cerebr. Blood Flow Metab.

Endothelium-dependent relaxation counteracting the contractile action of endothelin-1 is partly due to ETB receptor activation

Res. exp. Med.

Null mutation of endothelin receptor type B gene in spotting lethal rats causes aganglionic megacolon and white coat color

Proc. natn. Acad. Sci. U.S.A.

Delayed loss of ETB-receptor-mediated vasorelaxation after cold lesion of the rat parietal cortex

J. cerebr. Blood Flow Metab.