The overall aim of this thesis was to analyze the expression of key vasoregulatory genes in the vascular endothelium and smooth muscle following hypoxia. Hypoxia caused a reversal in endothelial cell function such that the vascular endothelium enhanced alpha-agonist induced contractions. Downregulation of endothelial nitric oxide synthase (eNOS) and impaired endothelium-dependent vasodilation were observed in the aortas of rats exposed to hypoxia for 12 and 48 hours. Following stimulation of aortic rings with acetylcholine, cyclic GMP and nitrite levels were also reduced. Decreased endothelial NO release may impair the vascular responses which defend vital organ oxygenation. This decrease in the capacity for vasodilator synthesis following hypoxia cannot by itself, however, mediate the observed enhancement of contractility. An increase in aortic endothelin-1 (ET-1) mRNA and protein was localized to the vascular endothelium. Treatment with the ET-1 receptor antagonist, BQ123, mimicked endothelial denudation and confirmed that locally secreted ET-1 accounts for endothelium-dependent enhancement of contractility. Concurrently, hypoxia caused an endothelium-independent impairment of smooth muscle reactivity to alpha-adrenoreceptor activation. Despite a decrease in eNOS in the aorta of rats exposed to hypoxia, Ca2+-dependent NOS activity remained unchanged suggesting the upregulation of neuronal NOS (nNOS). In endothelium-denuded aortic rings from hypoxic rats, L-NAME enhanced the contractile response to phenylephrine. In addition, it normalized the hypoxia-induced hypocontractility in intact aortic rings. The presence of nNOS was confirmed by Western blot analysis, immunohistochemistry, in situ hybridization and RT-PCR. Rat nNOS mRNA transcript bearing the alternately spliced exon 1b was shown to be expressed in the medial layer of aortas from hypoxic rats and in vascular smooth muscle cells cultured under hypoxic conditions. Cloning and analysis of the 5' regulatory
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.37849 |
| Date | January 2000 |
| Creators | Topors, Mourad. |
| Contributors | Ward, Michael E. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001802356, proquestno: NQ70166, Theses scanned by UMI/ProQuest. |
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