APLN and pulmonary hypertension: Additionally, circulating levels of apelin are decreased in chronic heart failure (Földes et al., 2003) and in essential and pulmonary hypertension (Sonmez et al., 2010; Chandra et al., 2011), and increased in disease states such as aortic stenosis (Duman et al., 2018), and left ventricular hypertrophy (Helske et al., 2010).