Conversely, in hypothyroidism, there is decreased myocardial contractility, cardiac output, and renal blood flow; decreased synthesis of vascular endothelial relaxation factor, resulting in arterial stiffness; increased systemic vascular resistance; and reduced sensitivity to β-adrenergic receptors and decreased renin expression and release, resulting in decreased RAAS activity [22]. Here, REN is linked to hypothyroidism.