Min-Soon Choi

Cyclooxygenase-derived products, rather than nitric oxide, are endothelium-derived relaxing factor(s) in the ventral aorta of carp (Cyprinus carpio)

In some fish blood vessels, the existence of a NO (nitric oxide) system has been reported. We examined the possibility that this NO system acts as an endothelium-derived relaxing factor (EDRF) in carp aorta using the carp aorta alone and in a combined carp-rat aorta donor-detector system. Use of the typical NO stimulating agent in mammal acetylcholine (ACh) only induced constriction of the carp aorta. This response was not modified by denudation or by NO synthesis inhibition with N-nitro-L-arginine methyl ester. Neither the indirect NO stimulating agents bradykinin and histamine nor the direct NO releasers sodium nitroprusside (SNP) and SIN-1 induced vasorelaxation. Both SNP and ACh elevated the cGMP concentration in rat aorta, but not in carp aorta. In the aorta combination set-up, where carp served as a NO donor and rat aorta served as a NO detector, no relaxation of the rat aorta was observed. The calcium ionophore A23187, a known EDRF producer in mammals, induced relaxation of carp aorta through an endothelium- and cyclooxygenase-dependent mechanism. These results indicate that carp aorta does not produce NO as an EDRF nor does it respond to exogenously supplied NO. The major EDRF in carp is apparently a product(s) of cyclooxygenase metabolism.