Urotensin II is a cyclic undecapeptide which activates the GPR14 receptor and exerts potent vasoconstrictor effects in some species of fish and mammals. The present study intended to investigate isolated vessels from various species in an attempt to find sensitive preparations to be used in studies of the human urotensin (hU-II)/GPR14 system. Contractile responses evoked by noradrenaline (NA), angiotensin II (Ang II), endothelin 1 (ET-1) and hU-II were measured in large vessels (aorta and some large arteries and veins) of rats, guinea pigs, rabbits, pigs and humans. Relaxing effects of hU-II, bradykinin (BK) and substance P (SP) were measured in pig coronary arteries contracted with KCl 30 mM. The rat mesenteric vasculature was investigated from the arterial and venous site to establish the function of ET-1 and hU-II receptors. Results indicate that the only preparation showing high sensitivity to hU-II (pEC(50)=8.27) is the rat aorta, whose contractions in response to hU-II develop slowly and persist for hours, similar to those of ET-1 (pEC(50)=8.35). Effects of NA (pEC(50)=8.12) and Ang II (pEC(50)=7.95) develop and reverse more rapidly. Tissues treated with ET-1 and hU-II show marked desensitization, in contrast to those treated with NA. Specific antagonists for alpha(1) (prazosin, p A(2)=10.46), AT(1) (EXP 3174, p A(2)=10.20), 5HT(2) (ketanserine, p A(2)=8.61) and ET(A)-ET(B) (bosentan, p A(2)=6.88) receptors were shown to block the effects of the respective agonists, while being inactive against hU-II. In some vessels, hU-II behaved as an highly potent but scarcely effective contractile agent. It is concluded that: the hU-II/GPR14 is not a functional contractile system in vessels of several species, in contrast with NA/alpha(1), Ang II/AT(1), 5HT/5HT(2) and ET-1/ET(A)-ET(B). The rat aorta appears however to be a sensitive and reliable preparation for evaluating biological activities of hU-II and related peptides.