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.

No abstract

In this study, the Galpha(qi5) protein was used to force the human nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor to signal through the Ca(2+) pathway in CHO cells. [Ca(2+)](i) levels were monitored using the fluorometer FlexStation II and the Ca(2+) dye Fluo 4 AM. Concentration response curves were generated with a panel of full and partial agonists, while NOP antagonists were assessed in inhibition-response curves. The following rank order of potency of antagonists was measured: SB - 612111 > J - 113397 = Trap - 101 > or = UFP - 101 > [Nphe1]N/OF Q(1 - 13)NH2 >> naloxone, which is superimposable to literature findings. The rank order of potency of full and partial agonists is also similar to that obtained in previous studies with the exception of a panel of ligands (UFP-112, Ro 64-6198, ZP120, UFP-113) whose potency was relatively low in the Galpha(qi5)-NOP receptor calcium assay. Interestingly, these NOP ligands are characterized by slow kinetic of interaction with the NOP receptor, as demonstrated by bioassay experiments. These results demonstrated that the FlexStation II-Galpha(qi5)-NOP receptor calcium assay represents an adequate and useful screening for NOP receptor ligands, particularly for antagonists.

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Neuropeptide S (NPSa), the endogenous ligand of a previously orphan receptor now named NPSR, regulates various biological functions in the brain, including arousal, locomotion, anxiety, and food intake. Here we report on a focused structure-activity study of Gly 5 which has been replaced with L and D amino acids. Fifteen NPS related peptides were synthesized and pharmacologically tested for intracellular calcium mobilization using HEK293 cells stably expressing the mouse NPSR