ML161 is a potent and selective antagonist of the apelin receptor (APJ), which plays a role in cardiovascular regulation, fluid homeostasis, and insulin signaling. It is primarily used in research settings to investigate the physiological and pathological functions of the apelin-APJ system. Applications include studying heart failure, hypertension, and metabolic disorders such as diabetes. ML161 helps block apelin-induced signaling in cellular and animal models, allowing scientists to dissect the receptor's contribution to disease mechanisms. Due to its high selectivity and pharmacological stability, it is a valuable tool in target validation and pathway analysis in cardiovascular and metabolic research.