Methods Sprague-Dawley rats, weighing 250 to 350 g and maintained on an ad lib water and standard rat chow diet, underwent right nephrectomy 2 weeks prior to being studied.

Natural history experiments Control measurements of blood urea nitrogen (BUN) were made in 12 randomly chosen rats. The animals were then anesthetized with pentobarbital (60 mg/kg ip); the left renal pedicle was exposed through a flank incision. A micropipette (35 s OD) mounted on a micromanipulator and attached to a motor-driven syringe was introduced into the renal artery. Norepinephrine (NE) was delivered through the pipette into the renal artery at 0.6 g/kg/min for 90 mm. The pipette was removed, the surgical wound was closed, and the rats were allowed to recover from anesthesia. They received ad lib water, a low potassium diet (ICN Pharmaceuticals, Cleveland, Ohio) for 48 hr and a regular diet thereafter. BUN was measured every third day for 25 days. C1 was measured at 4 weeks in the five remaining rats and 12 control rats that had been infused with 0.9% saline intrarenally at the same time ARF rats had received NE.