Nitric oxide, a potent vasodilator of the aortic anastomosis in the estuarine crocodile, Crocodylus porosus

The effects of five neuropeptides (CGRP, SOM, SP, NPY, VIP), L-NAME (nitric oxide synthase inhibitor), and adrenaline on the contractile tone of the a ortic anastomosis in the estuarine crocodile, Crocodylus porosus, were inve stigated. None of the neuropeptides, which had previously been found to be present in the aortic anastomosis, had any direct effect on the tension dev eloped by ring preparations. L-NAME itself significantly increased the basa l tone of the vascular ring preparations, suggesting a tonic release of nit ric oxide in the preparation. Adrenaline produced concentration-dependent v asoconstrictions that were counteracted by profound reflex vasodilatations that were susceptible to blockade by L-NAME. Immunohistochemistry revealed the presence of nitric oxide synthase and tyrosine hydroxylase-containing ( indicating the presence of a adrenergic innervation) nerve fibres in the ad ventitia and adventitio-medial border of the aortic anastomosis. These data demonstrate opposing actions of adrenaline and nitric oxide on the vascula r smooth muscle in the anastomosis of the C. porosus. The morphology of the anastomosis, with the extremely thick muscular vessel wall, suggests a sph incter-like function for this vessel that could be controlled mainly by adr energic and nitrergic mechanisms, (C) 2001 Academic Press.