Effect of YM471, an orally active non-peptide arginine vasopressin receptor antagonist, on human vascular smooth muscle cells

Objective: To investigate the effects of YM471, a non-peptide arginine vasopressin (AVP) V_1A and V₂ receptor antagonist, on the AVP-induced growth responses in human vascular smooth muscle cells (VSMCs). Methods: Binding of YM471 to V_1A receptors on VSMCs was measured using [³H]AVP. Intracellular free Ca²⁺ concentration was measured by fura 2 fluorescence. Mitogen-activated protein (MAP) kinase activity was determined using the p42/p44 MAP kinase specific peptide and [γ-³²P]ATP as substrates. The effect of AVP on hyperplasia and hypertrophy of VSMCs was determined by cell number and protein content measurements. Results: YM471 potently and concentration-dependently inhibited the specific binding of [³H]AVP to V_1A receptors on VSMCs, exhibiting an inhibition constant (K_i) of 0.35 nmol/l. YM471 inhibited the AVP-induced increase in intracellular free Ca²⁺ concentration with an 50% inhibition concentration (IC₅₀) of 2.01 nmol/l and inhibited the activation of MAP kinase with an IC₅₀ of 6.11 nmol/l. In addition, AVP concentration-dependently induced hyperplasia and hypertrophy in VSMCs, but YM471 prevented these AVP-induced growth effects, exhibiting IC₅₀ values of 2.31 and 0.23 nmol/l, respectively. Conclusions: These results indicate that YM471 has high affinity for V_1A receptors on, and potently inhibits AVP-induced physiologic responses of, human VSMCs.