Effects of Renal Arterial Endothelin-1 and Endogenous Endothelins on Regional Kidney Blood Flow and Renal Antihypertensive Mechanisms in Anesthetized Rabbits

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Abstract
To determine how endothelins affect regional kidney blood flow and responses to increased renal artery pressure (RAP), an extracorporeal circuit was established to control RAP independent of the mean systemic arterial pressure (MAP). RAP was first set at ∼65 mm Hg, and endothelin-1 (1 ng/kg/min for 30 min then 0.4 ng/kg/min) or vehicle was infused into the renal artery, or the ETA/ETB antagonist TAK-044 (3 mg/kg plus 3 mg/kg/h) or vehicle was administered intravenously. RAP was then progressively increased in steps from ∼65 to ∼160 mm Hg. When RAP was ∼65 mm Hg, endothelin-1 increased renal vascular resistance (RVR, 72%), and reduced cortical (CBF, 26%) but not medullary blood flow (MBF). TAK-044 reduced MAP (12%) and RVR (15%) and increased CBF (21%) but not MBF. When RAP was increased, renal blood flow (RBF), glomerular filtration rate, and urine and sodium excretion increased, while MAP fell. These responses were unaffected by endothelin-1. TAK-044 potentiated the increases in RBF and reductions in MAP in response to increased RAP, but did not affect urine and sodium excretion. Plasma renin activity was reduced by endothelin-1 and increased by TAK-044. Thus, both exogenous and endogenous endothelins reduce CBF but not MBF, and reduce plasma renin activity, but neither affect pressure natriuresis.