Modulation of renal medullary ionic hypertonicity by prostaglandins: data from tissue admittance studies in the rat

1. Modulation of the cortico-papillary electrolyte gradient by prostaglandins (PG) was studied in the kidney of anaesthetized rats. The intrarenal PG activity was varied by synthesis blockade with indomethacin (Ind) or meclophenamate (Me) and by intrarenal infusion of prostaglandin E2 (PGE2). 2. The interstitial electrolyte concentration in the medulla was continuously recorded in the kidney in situ as tissue electrical admittance (reciprocal impedance); the total renal blood flow (RBF), inulin clearance (Cin) and renal excretion were measured simultaneously. 3. Indomethacin and Me (15 mg kg-1 h-1) increased tissue admittance 15-20% in the inner and 12-15% in the outer medulla (P < 0.001) whereas PGE2 (300 ng kg-1 min-1) decreased admittance 14 and 8%, respectively (P < 0.01). 4. Renal blood flow and Cin were not affected by intrarenal PG activity changes. There was an increase in urine concentration after PG blockade and a delayed decrease after PGE2 infusion. 5. A joint analysis of the dynamics of medullary tissue admittance, renal haemodynamics and renal excretion provides evidence that PGs modify the medullary ionic hypertonicity by affecting NaCl transport in the ascending limb of the loop of Henle.