REN and hypertensive disorder: One reason for this poor understanding is that the pathophysiology of hypertension is complex, with contributions from the sympathetic nervous system, the renin-angiotensin-aldosterone system, and the immune system each implicated in its cause.2–5 Notwithstanding, the adverse effects of hypertension are mediated by changes in the structure and function of the artery wall.6–8 Functional changes, in the form of altered vascular reactivity, occur at the earliest stages of hypertension and contribute to the development and reinforcement of the condition.