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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


Figure 1
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  		Fig. 1. Effects of increasing concentration of serotonin (5-HT; A), endothelin-1 (ET-1; B) and noradrenaline (NA; C), on the relative tension of alligator intrapulmonary arteries. The effects of NA were evaluated on relaxed vessels as well as vessels preconstricted with ET-1 (10–8 mol l–1) before and after incubation with propranolol (10–5 mol l–1). Contraction is expressed relative to the contraction induced by 60 mmol l–1 KPSS and relaxation is given as a percentage of the precontraction. Values are means ± s.e.m.; each dose–response relationship is based on six blood vessels from six different animals, using a total of 13 alligators. An asterisk indicates a significant difference (P<0.05) from control values evaluated by a one-way ANOVA for repeated measures or a two-way ANOVA followed by Dunnett's post hoc test.

 

Figure 2
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  		Fig. 2. Original tension recordings showing the effects of hypoxia (PO2<5 mmHg) on an alligator intrapulmonary artery, internal circumference 1086 µm, preconstricted with endothelin-1 (ET-1; 10–8 mol l–1). The hypoxic constriction is compared to the constriction induced by KPSS (60 mmol l–1). The degree of relaxation with acetylcholine (ACh; 10–5 mol l–1) verifies an intact endothelium; W, wash with PSS.

 

Figure 3
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  		Fig. 3. Effects of hypoxia (45 min, PO2<5 mmHg) on alligator intrapulmonary arteries. (A) Relaxed vessels (baseline), (B) vessels preconstricted with serotonin (5-HT) and (C) vessels preconstricted with endothelin-1 (ET-1) with an intact endothelium (black bars) or denuded (grey bars). Contraction is expressed relative to the contraction induced by 60 mmol l–1 KPSS. Values are means ± s.e.m., N=3 (A) and N=6 (B,C). Different letters indicate a significant difference (P<0.05) from baseline evaluated by a two-way ANOVA followed by a Tukey post hoc test. Haematoxylin/Eosin staining shows the presence (D) and absence (E) of endothelium in representative vessels (40xmagnifications). The arrow shows endothelial cells.

 

Figure 4
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  		Fig. 4. Effects of increasing concentrations of endothelin-1 (ET-1) on the relative tension of alligator intrapulmonary arteries: non-treated vessels, vessels incubated with either the specific ETA-receptor antagonist BQ-123 (3x10–6 mol l–1), the specific ETB-receptor antagonist BQ-788 (3x10–6 mol l–1) or the general ET-receptor antagonist tezosentan (10–5 mol l–1). Contraction is expressed relative to the contraction induced by 60 mmol l–1 KPSS. Values are means ± s.e.m., N=7 (ET-1) and N=4 (ETB, ETA and tezosentan). An asterisk denotes a significant difference (P<0.05) from control treatment with ET-1 alone, evaluated by a two-way ANOVA followed by a Tukey post hoc test.

 

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  		Fig. 5. Representative micrographs showing immunofluorescent staining with anti-ETA (A,D) and anti-ETB (B,E) receptor antibodies in longitudinal sections of an alligator intra-pulmonary artery (internal circumference: 586 µm). (C,F) Negative controls. (A,B) strong staining for ETA-receptors and weaker staining for ETB-receptors in media and adventitia (20xmagnification). (D,E) strong staining for ETA-receptors and weaker staining for ETB-receptors in endothelial cells (40xmagnification). Arrows in D,E indicate epithelial cells.

 

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