Intrarenal ATI receptor blockade enhances renal autoregulation in anesthetized dogs

Regulation of renal vascular resistance in response to changes in renal perfusion pressure (autoregulation) in the juxtamedullary cortex and inner medulla, may be critical to the overall functioning of the kidney. We compared thejuxtamedullary and papillary regions in their ability to maintain blood flow during step changes in renal perfusion pressure (RPP) of volume expanded anesthetized dogs. Fiberoptic probes (0.5 mm o.d.) were inserted into the renal parenchyma at depths of 10-12 mm and 17-20 mm for the measurement of juxtamedullary blood flow and papillary flow, respectively. Dogs were maintained in sodium and water diuresis by infusion of 0.9% saline (3 ml/min) and 5% dextrose in water (4 ml/min). RPP was lowered both before and during intrarenal angiotensin II (ATI) receptor blockade with Losartan (30 ug/kg/min). In control, reductions in RPP from 131 to 65 mmHg decreased whole kidney blood flow by 28.4%, juxtamedullary flow by 32.0% and papillary flow by 20.6%. After ATI receptor blockade, whole kidney flow decreased by only 6.6% and juxtamedullary and papillary flows increased by 4.9 and 0 7%, respectively, over this same range of RPP. Despite positive free water clearance and volume expansion, plasma AVP ranged from 7-11 pg/ml Thus, the canine kidney is capable of maintaining constant blood flow within both the outer and inner medulla over a wide range of RPP. This autoregulatory ability is enhanced b> intrarenal ATI receptor blockade with Losartan. We conclude that in anesthetized dogs, renal blood flow is uniformly autoregulated within the kidney parallel to whole kidney blood flow Medullary autoregulation is modulated in part b\ intrarenal All constriction via ATI receptors.