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J Auton Nerv Syst. 1997 Mar 19;63(1-2):68-76.

Vip-induced relaxation of small arteries of the rainbow trout, Oncorhynchus mykiss, involves prostaglandin synthesis but not nitric oxide.

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Department of Zoophysiology, Göteborg University, Sweden.


Small arteries (internal diameter 376 +/- 69 microns) from the proximal intestine region of the rainbow trout were mounted in a myograph apparatus where changes in isometric tension could be recorded. VIP (vasoactive intestinal polypeptide) caused a concentration-dependent relaxation (10(-9)-3 x 10(-7) M) of vessels precontracted with the alpha-adrenoceptor agonist phenylephrine (10(-5) M). The nitric oxide synthase inhibitor L-NAME (10(-4) M) did not affect the VIP-relaxation, neither did the lipoxygenase inhibitor esculetin (10(-5) M). However, the cyclooxygenase inhibitor indomethacin (10(-6) M) shifted the concentration-response curve significantly to the right. The VIP-relaxation was still present after mechanical removal of the endothelium. Sodium nitroprusside (10(-9)-10(-6) M) caused a concentration-dependent relaxation of the precontracted vessel, indicating the presence of soluble guanylate cyclase in the vascular smooth muscle cells. VIP-immunoreactivity was found in varicose nerve fibers in these vessels, but nitric oxide synthase-immunoreactivity could not be demonstrated. These results suggest that in rainbow trout, as in mammals, VIP is an endogenous vasodilating neuropeptide. No endothelium-dependent mechanism seems to be involved, neither is production of nitric oxide. Instead the relaxation is mediated, at least in part, via prostaglandin synthesis.

[Indexed for MEDLINE]

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