Synergistic effect of urotensin II with serotonin on vascular smooth muscle cell proliferation

BACKGROUND Urotensin II (U-II), the most potent vasoconstrictor, and serotonin (5-HT) are known to play an important role in pulmonary hypertension. However, little is known about the effect of U-II and its interaction with 5-HT on vascular smooth muscle cell (VSMC) proliferation. OBJECTIVE We assessed the interaction between U-II and 5-HT in inducing VSMC proliferation. METHODS Growth-arrested rabbit VSMCs were incubated in serum-free medium with different concentrations of U-II and 5-HT. VSMC proliferation was examined by the increase in [H]thymidine incorporation into DNA and cell number. RESULTS U-II or 5-HT induced [H]thymidine incorporation in a dose-dependent manner with a maximal effect at a concentration of 50 nmol/l (161%) or 50 μmol/l (205%), respectively. When added together, low concentrations of U-II (50 nmol/l) and 5-HT (1 μmol/l) interacted synergistically in inducing [H]thymidine incorporation (382%). These effects on [H]thymidine incorporation were paralleled by an increase in cell number. The G-protein inactivator GDP-β-S (100 μmol/l), protein kinase C (PKC) inhibitor Ro31-8220 (0.1 μmol/l), Src family tyrosine kinase inhibitor PP2 (1 μmol/l), and mitogen-activated protein kinase (MAPK) kinase inhibitor PD098059 (10 μmol/l) inhibited the mitogenic effects of U-II and 5-HT and also their interaction in inducing [H]thymidine incorporation. CONCLUSION Our results suggest that U-II and 5-HT may induce the synergistic interaction in inducing VSMC proliferation via a G-protein-coupled receptor/PKC/Src tyrosine kinase/MAPK pathway, thus contributing to the relatively rapid development of atherosclerosis in hypertensive vascular disease.