EFFECTS OF DAILY SODIUM-INTAKE AND ANG-II ON CORTICAL AND MEDULLARY RENAL BLOOD-FLOW IN CONSCIOUS RATS

Implanted optical fibers and laser-Doppler flow measurement techniques were used for the sequential measurement of regional renal blood flow in conscious rats to determine the effects of an increase of daily Na Cl intake on the renal cortical blood flow and blood flow to the outer and inner medulla. Cortical blood flow was increased significantly (3 2%) by the second day when NaCl intake was increased from 1 to 7 meq/d ay and was increased further (50%) on the second day after a further e levation of NaCl intake to 13 meq/day. Blood flow to the outer and inn er medulla was not changed as NaCl intake was elevated. The increase i n renal cortical flow was closely associated with significant reductio ns in circulating concentrations of ANG II from 31 to 16 pg/ml. Rats g iven a continuous infusion of nonpressor doses of ANG II (5.0 ng.kg(-1 ).min(-1)) to maintain constant plasma concentrations of ANG II as sod ium intake was increased exhibited no increase of cortical flow. We co nclude that reductions of plasma ANG II associated with incremental in creases of daily sodium intake result in a rise of renal cortical flow . The elevated blood flow to the renal cortex may enhance sodium excre tion and contribute to long-term sodium homeostasis.