Human urotensin II as a link between hypertension and coronary artery disease

Hemodynamic effects of urotensin II and its specific receptor antagonist palosuran in cirrhotic rats

In cirrhosis, splanchnic vasodilation contributes to portal hypertension, subsequent renal sodium retention, and formation of ascites. Urotensin II(U-II) is a constrictor of large conductive vessels. Conversely, it relaxes mesenteric vessels, decreases glomerular filtration, and increases renal sodium retention. In patients with cirrhosis, U-II plasma levels are increased. Thus, we investigated hemodynamic and renal effects of U-II and its receptor antagonist, palosuran, in cirrhotic bile duct-ligated rats (BDL). In BDL and sham-operated rats, we studied acute effects of U-II (3 nmol/kg; intravenously) and palosuran (10 mg/kg; intravenously) and effects of oral administration of palosuran (30 mg/kg/day; 3 days) on hemodynamics and renal function. We localized U-II and U-II-receptor (UTR) in livers and portal veins by immunostaining. We determined U-II-plasma levels by enzyme-linked immunosorbent assay (ELISA), and mesenteric nitrite/nitrate-levels by Griess-reaction. RhoA/Rho-kinase and endothelial nitric oxide synthase (eNOS) pathways were determined by western blot analysis and reverse transcription polymerase chain reaction (RT-PCR) in mesenteric arteries. U-II plasma levels, as well as U-II and UTR-receptor expression in livers and portal veins of cirrhotic rats were significantly increased. U-II administration further augmented the increased portal pressure (PP) and decreased mean arterial pressure (MAP), whereas palosuran decreased PP without affecting MAP. The decrease in PP was associated with an increase in splanchnic vascular resistance. In mesenteric vessels, palosuran treatment up-regulated expression of RhoA and Rho-kinase, increased Rho-kinase-activity, and diminished nitric oxide (NO)/cyclic guanosine 3',5'-monophosphate (cGMP) signaling. Moreover, palosuran increased renal blood flow, sodium, and water excretion in BDL rats.

CONCLUSION

In BDL rats, U-II is a mediator of splanchnic vasodilation, portal hypertension and renal sodium retention. The U-II-receptor antagonist palosuran might represent a new therapeutic option in liver cirrhosis with portal hypertension.

Urotensin II acutely increases myocardial length and distensibility: potential implications for diastolic function and ventricular remodeling

Urotensin II (U-II) is a cyclic peptide that may be involved in cardiovascular dysfunction. In the present study, the acute effects of U-II on diastolic properties of the myocardium were investigated. Increasing concentrations of U-II (10(-8) to 10(-6) M) were added to rabbit papillary muscles in the absence (n = 15) or presence of: (1) damaged endocardial endothelium (EE; n = 9); (2) U-II receptor antagonist, urantide (10(-5) M; n = 7); (3) nitric oxide (NO) synthase inhibitor, N(G)-Nitro-L-Arginine (10(-5) M; n = 9); (4) cyclooxygenase inhibitor, indomethacin (10(-5) M; n = 8); (5) NO synthase and cyclooxygenase inhibitors, N(G)-Nitro-L-Arginine (10(-5) M) and indomethacin (10(-5) M), respectively, (n = 8); or (6) protein kinase C (PKC) inhibitor, chelerythrine (10(-5) M; n = 9). Passive length-tension relations were constructed before and after a single concentration of U-II (10(-6) M; n = 3). U-II concentration dependently decreased inotropy and increased resting muscle length (RL). At 10(-6) M, active tension decreased 13.8 +/- 5.4%, and RL increased to 1.007 +/- 0.001 L/L (max). Correcting RL to its initial value resulted in an 18.1 +/- 3.0% decrease in resting tension, indicating decreased muscle stiffness, which was also suggested by the down and rightward shift of the passive length-tension relation. This effect remained unaffected by EE damage and PKC inhibition. In contrast, the presence of urantide and NO inhibition abolished the effects of U-II on myocardial stiffness, while cyclooxygenase inhibition significantly attenuated them. U-II decreases myocardial stiffness, an effect that is mediated by the urotensin-II receptor, NO, and prostaglandins. This represents a novel mechanism of acute neurohumoral modulation of diastolic function, suggesting that U-II is an important regulator of cardiac filling.

Human Urotensin-II Potentiates the Mitogenic Effect of Mildly Oxidized Low-Density Lipoprotein on Vascular Smooth Muscle Cells: Comparison with Other Vasoactive Agents and Hydrogen Peroxide

Human urotensin-II (U-II) is the most potent vasoactive peptide identified to date, and may be involved in hypertension and atherosclerosis. We investigated the effects of the interactions between U-II or other vasoactive agents and mildly oxidized low-density lipoprotein (mox-LDL) or hydrogen peroxide (H2O2) on the induction of vascular smooth muscle cell (VSMC) proliferation. Growth-arrested rabbit VSMCs were incubated with vasoactive agents (U-II, endothelin-1, angiotensin-II, serotonin, or thromboxane-A2) in the presence or absence of mox-LDL or H2O2. [3H]Thymidine incorporation into DNA was measured as an index of VSMC proliferation. On interaction with mox-LDL or H2O2, U-II induced the greatest increase in [3H]thymidine incorporation among these vasoactive agents. A low concentration of U-II (10 nmol/l) enhanced the potential mitogenic effect of low concentrations of mox-LDL (120 to 337%) and H2O2 (177 to 226%). U-II at 50 nmol/l showed the maximal mitogenic effect (161%), which was abolished by G protein inactivator (GDP-beta-S), c-Src tyrosine kinase inhibitor (radicicol), protein kinase C (PKC) inhibitor (Ro31-8220), extracellular signal-regulated kinase (ERK) kinase inhibitor (PD98059), or Rho kinase inhibitor (Y27632). Mox-LDL at 5 microg/ml showed the maximal mitogenic effect (211%), which was inhibited by free radical scavenger (catalase), intracellular and extracellular antioxidants (N-acetylcysteine and probucol), nicotinamide adenine dinucleotide phosphate oxidase inhibitor (diphenylene iodonium), or c-Jun N-terminal kinase (JNK) inhibitor (SP600125). These results suggested that U-II acts in synergy with mox-LDL in inducing VSMC DNA synthesis at the highest rate among these vasoactive agents. Activation of the G protein/c-Src/PKC/ERK and Rho kinase pathways by U-II together with the redox-sensitive JNK pathway by mox-LDL may explain the synergistic interaction between these agents.