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First published online May 2, 2008
Journal of Experimental Biology 211, 1565-1570 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.014662
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Hypoxia-induced vasoconstriction in alligator (Alligator mississippiensis) intrapulmonary arteries: a role for endothelin-1?

Nini Skovgaard1,2,*, Helle Zibrandtsen2, Britt Elmedal Laursen2, Ulf Simonsen2 and Tobias Wang1

1 Zoophysiology, Department of Biological Sciences, University of Aarhus, Building 1131, 8000 Aarhus C, Denmark
2 Department of Pharmacology, University of Aarhus, Denmark

* Author for correspondence (e-mail: nini.jensen{at}biology.au.dk)

Accepted 17 March 2008

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive response that diverts pulmonary blood flow from poorly ventilated and hypoxic areas of the lung to better ventilated parts, matching blood perfusion to ventilation. HPV is an ancient and highly conserved response expressed in the respiratory organs of all vertebrates. However, the underlying mechanism and the role of the endothelium remain elusive. Isolated intrapulmonary arteries (internal diameter <346 µm) from the American alligator Alligator mississippiensis were mounted in microvascular myographs for isometric tension recording. Resting vessels and vessels contracted with either serotonin (5-HT) or endothelin-1 (ET-1) were exposed to sustained (45 min) hypoxia (PO2<5 mmHg). In ET-1-contracted vessels, hypoxia induced a monophasic, sustained and fully reversible constriction, which was independent of the endothelium. In relaxed or in 5-HT-contracted vessels, hypoxia did not cause constriction. The effects of ET-1, ETA and ETB as well as the general ET-receptor antagonist were studied. ET-1 caused a contraction of the pulmonary arteries through stimulation of ETA-receptors. ETA and ETB immunoreactive staining revealed the location of both receptors in the smooth muscle layer and of ETB receptors in the endothelium. In conclusion, because precontraction with serotonin did not facilitate HPV, the required precontraction in alligators seems specific to ET-1, which implies that ET-1 plays an important permissive role for the HPV response in alligators.

Key words: reptile, alligator, hypoxic pulmonary vasoconstriction, endothelin-1, ETA-receptor, ETB-receptor, serotonin, noradrenaline


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