What is the role of the renin-angiotensin-aldosterone system (RAAS) in the pathophysiology of renovascular hypertension (RVHT)?

Updated: Dec 01, 2020
  • Author: Rebecca J Schmidt, DO, FACP, FASN; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

Angiotensin II exerts a vasoconstrictive effect on both afferent and efferent arterioles, but because the efferent arteriole has a smaller basal diameter, the increase in efferent resistance exceeds the increase in afferent resistance. Afferent vasoconstriction is further minimized by angiotensin II–mediated release of vasodilatory prostaglandins and nitric oxide. In addition, angiotensin II can constrict the glomerular mesangium, thereby reducing the surface area available for filtration.

The net effect of angiotensin II on filtration invokes the opposing factors of reduced renal blood flow and mesangial surface area (causing a decrease in filtration) and the increase in glomerular capillary pressure (which tends to increase filtration). The end result depends on the clinical setting in which it occurs.

In the healthy kidney, a fall in systemic blood pressure activates the RAAS, which triggers a decrease in renal blood flow secondary to increased renal vascular (afferent) resistance. The preferential increase in efferent resistance mediated by angiotensin II results in increased glomerular capillary hydraulic pressure, which maintains the glomerular filtration rate (GFR).

In the ischemic kidney with reduced afferent blood flow, intraglomerular pressure and glomerular filtration are maintained by and depend upon angiotensin II–mediated efferent vasoconstriction. In this setting, removal of the efferent vasoconstrictive effect by angiotensin blockade, as achieved by angiotensin-converting enzyme (ACE) inhibitors, results in a decrease in intraglomerular pressure and GFR.

Thus, in patients with renovascular disease, particularly those with bilateral RAS or those with a stenotic renal artery to a single kidney, ACE inhibitors may cause a deterioration of renal function and azotemia. The propensity for angiotensin receptor blockers (ARBs) to affect GFR adversely is based on similar pathophysiology. It should be kept in mind that an acute decline in renal function in this setting is reversible once the ACE inhibitor (or the ARB) is discontinued. [2]


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