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First published online December 14, 2006
Journal of Experimental Biology 210, 129-137 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02620

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Dual mechanisms for nitric oxide control of large arteries in the estuarine crocodile Crocodylus porosus

Brad R. S. Broughton^* and John A. Donald

School of Life and Environmental Sciences, Deakin University, Geelong, Victoria, 3217, Australia

View larger version (121K): [in this window] [in a new window]   Fig. 1. Photomicrographs showing whole-mount (A,B,D) and sectioned (C) preparations of the crocodile right aorta (A), vena cava (B), aortic anastomosis (C) and dorsal aorta (D) following processing for NADPH-d histochemistry (A-C) and endothelial NOS IHC (D). In all vessels, punctate endothelial NOS-positive staining (arrowheads) occurred around the nuclei (arrows) of the endothelial cells. Scale bars, 10 µm.

View larger version (109K): [in this window] [in a new window]   Fig. 2. Photomicrographs showing wholemount preparations of the crocodile right aorta (A), vena cava (B), aortic anatomosis (C) and dorsal aorta (D) following processing for NADPH-d histochemistry (A,D) and neural NOS IHC (B,C,). A moderate plexus of neural NOS-positive perivascular nerve fibres (arrows) was observed in the outer layers of the wall of each vessel. In addition, some neural NOS-positive perivascular nerve bundles (arrowhead) were observed. Scale bars, 100 µm.

View larger version (8K): [in this window] [in a new window]   Fig. 3. Tension recordings showing the effect of SNP (A), ACh (B) and nicotine (C) on the crocodile right aorta (A,C) and dorsal aorta (B). The vessels were incubated with ET-1 (10-8 mol l-1) until a maximal constriction was achieved, and then either SNP (10-4 mol l-1), ACh (10-5 mol l-1), or nicotine (3x10-4 mol l-1) was added. All three chemicals caused a marked vasodilation. (D) Mean response of pre-constricted right aorta (filled bars) and dorsal aorta (open bars) to SNP (10-4 mol l-1), ACh (10-5 mol l-1) and nicotine (3x10-4 mol l-1). Values are means ± s.e.m., N=5.

View larger version (7K): [in this window] [in a new window]   Fig. 4. Tension recordings showing the effect of ACh (A-D), SNP (A-D) and rANP (B) on the crocodile right aorta in the presence of ODQ (B), L-NNA (C) and atropine (D). The aortae were pre-treated with ODQ (10-5 mol l-1), L-NNA (10-4 mol l-1) or atropine (10-6 mol l-1) for approximately 10 min before being constricted with ET-1 (10-8 mol l-1). Once maximal constriction was achieved, ACh (10-5 mol l-1) was added, followed by SNP (10-4 mol l-1); rANP was added to vessels pre-treated with ODQ only. The ACh-mediated vasodilation was abolished in the presence of ODQ, L-NNA and atropine, whereas the SNP-mediated vasodilation was only abolished by ODQ. Rat ANP induced a potent vasodilation in the presence of ODQ (N=5).

View larger version (5K): [in this window] [in a new window]   Fig. 5. Tension recordings showing the effect of nicotine (A-C), rANP (B) and SNP (C) on the crocodile dorsal aorta in the presence of ODQ (B) and L-NNA (C). The aortae were pre-treated with ODQ (10-5 mol l-1) or L-NNA (10-4 mol l-1) for approximately 10 min before being constricted with ET-1 (10-8 mol l-1). Once maximal constriction was achieved, nicotine (3x10-4 mol l-1) was added, followed by either rANP (10-8 mol l-1), which was added to the vessels pre-treated with ODQ, or SNP (10-4 mol l-1), which was added to the vessels pre-treated with L-NNA. The nicotine-mediated vasodilation was abolished in the presence of ODQ or L-NNA, but rANP and SNP both induced a potent vasodilation in the presence of ODQ and L-NNA, respectively (N=5).

View larger version (10K): [in this window] [in a new window]   Fig. 6. Tension recordings showing the effect of ACh on the crocodile right aorta with the endothelium intact (A) and with the endothelium removed (B). Haematoxylin and Eosin staining was used to verify that the endothelium was present or removed (see inset). The preparations were exposed to ET-1 (10-8 mol l-1) until a maximum constriction was achieved, and then ACh (10-5 mol l-1) was added. Acetylcholine only induced a vasodilation in the vessels with the endothelium intact (N=5).

View larger version (16K): [in this window] [in a new window]   Fig. 7. Tension recordings showing the vasodilatory effect of nicotine on the crocodile right aorta with the endothelium intact (A) and with the endothelium removed (B). Haematoxylin and Eosin staining was used to verify that the endothelium was present or removed (see inset). The preparations were exposed to ET-1 (10-8 mol l-1) until a maximum constriction was achieved and then nicotine (3x10-4 mol l-1) was added. Nicotine induced a vasodilation in both preparations. The lower graph shows the mean response of nicotine on pre-constricted right and dorsal aortae with the endothelium intact (filled bars) or the endothelium removed (open bars). There is no significant difference in the nicotine-mediated vasodilation with or without the endothelium (right aorta, P=0.52, dorsal aorta, P=0.63, N=5).