Urotensin-II is a nitric oxide-dependent vasodilator in the pial arteries of the newborn pig

Urotensin-II (UT-II) is a small circular peptide and is described as the most potent endogenous vasoconstrictor in various vascular beds. However, the in vivo effects of UT-II can be either vasoconstriction or vasodilation depending on the species and the tissue investigated. The present study sought to characterize the vasoactive effect of UT-II in the piglet cerebral circulation in vivo. Pial arteries of 99 +/- 6 mu m were visualized with intravital microscopy through a closed cranial window in anesthetized newborn piglets. Topical application of UT-II elicited a weak dose-dependent vasodilation of the arteries (0.001 mu M: 3 +/- 3 mu m, 0.1 mu M: 10 +/- 5 mu m, 10 mu M: 14 +/- 7 mu m). Smaller arteries with an initial diameter below 100 gm showed minimal or no vasodilation, while larger arteries between 100 and 120 gm had a pronounced dose-dependent effect. Systemic application of 15 mg/kg N-omega-nitro-L-arginine-methyl ester (L-NAME) completely inhibited the vasodilation. We conclude that UT-II, in contrast to most other vascular beds, is a weak NO-dependent vasodilator in the piglet pial vasculature. (c) 2005 Elsevier Inc. All rights reserved.