APLN and Hypertension: In peripheral tissues the apelinergic system appears to be down-regulated in hypertensive disease – levels of apelin immunoreactivity in plasma, and in ventricular and aortic tissues, are lower in the spontaneously hypertensive rat, a genetic model of hypertension, than in control Wistar-Kyoto normotensive rats (Zhang et al., 2006b, Zhang et al., 2006a, Zhong et al., 2005).