Abstract
With the failure of the heart as a pump, there ensues a series of neurohumoral compensations that defend organ perfusion at the expense of alterations in cardiac filling pressures and the distribution of blood flow to various regional circulations. Activation of the sympathetic nervous system and the renin-angiotensin II-aldosterone system and increases in circulating arginine vasopressin maintain arterial blood pressure by producing systemic arteriolar vasoconstriction and the renal retention of salt and water. Constriction of the efferent arterioles in the kidney by angiotensin II and norepinephrine promotes reabsorption of glomerular filtrate in the peritubular capillaries and maintains glomerular filtration in the face of declines in glomerular plasma flow and the glomerular permeability-surface area ultrafiltration coefficient. In resting, sodium-replete, conscious animals and humans, pharmacologic inhibition of renal cyclo-oxygenase by nonsteroidal anti-inflammatory drugs has little or no effect on renal hemodynamics. However, electrical or reflex stimulation of the renal nerves, intrarenal infusion of angiotensin II, or infusion of arginine vasopressin stimulates the release of vasodilator prostaglandins from the kidneys. In sodium-depleted animals or humans, and when cardiac output decreases, there is an increase in total peripheral vascular resistance but little change in renal vascular resistance. Increased renal synthesis of vasodilator prostaglandins (presumably by the blood vessels) maintains renal blood flow despite increased release of renin and norepinephrine from the kidneys. In these situations, pharmacologic inhibition of renal cyclo-oxygenase is accompanied by marked reductions in renal blood flow and glomerular filtration rate. When this occurs in patients with advanced heart failure, reversible oliguric renal failure may result. In this setting, cyclo-oxygenase inhibition may also increase arterial pressure and induce additional depression of cardiac function. Recent data indicate that blood vessels have the capacity to synthesize the sulfidopeptide leukotrienes C4, D4, and E4, which can constrict peripheral and renal blood vessels and alter vascular permeability. The vascular cell types responsible for leukotriene C4 synthesis and the potential roles of these vasoactive eicosanoids in kidney and other regional circulations are currently under study.
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