RS 127445 HCl (CAS 199864-87-4) is a small-molecule antagonist targeting the serotonin 5-HT2B receptor a member of the G-protein coupled receptor family It is designed to selectively block 5-HT2B receptor activity thereby modulating intracellular signaling pathways such as calcium elevation and inositol phosphate production RS 127445 HCl exerts its biological activity primarily through selective antagonism of the 5-HT2B receptor In isolated tissue preparations such as rat stomach fundus and jugular vein RS 127445 HCl inhibits serotonin-induced contraction Based on these pharmacological properties RS 127445 HCl holds research potential in studies of 5-HT2B receptor function and related physiological processes