Il

Renal and systemic I vasoconstriction I

t Vascular smooth muscle sensitivity to vasoconstrictors

Cyclosporin A ! Angiotensin iz

Striped interstitial fibrosis

Tubular cell injury r

Striped interstitial fibrosis

Mechanisms that contribute to decreased glomerular filtration rate (GFR) in acute renal failure. After exposure to a nephrotoxicant, one or more mechanisms may contribute to a reduction in the GFR. These include renal vasoconstriction resulting in prerenal azotemia (eg, cyclosporin A) and obstruction due to precipitation of a drug or endogenous substances within the kidney or collecting ducts (eg, methotrexate). Intrarenal factors include direct tubular obstruction and dysfunction resulting in tubular backleak and increased tubular pressure. Alterations in the levels of a variety of vasoactive mediators (eg, prostaglandins following treatment with nonsteroidal anti-inflammatory drugs) may result in decreased renal perfusion pressure or efferent arteriolar tone and increased afferent arteriolar tone, resulting in decreased in glomerular hydrostatic pressure. Some nephrotoxicants may decrease glomerular function, leading to proteinuria and decreased renal function.

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