Evidence for redistribution of filtrate among nephrons after beta-adrenergic stimulation and blockade

Summary Renal excretion of fluid and electrolytes, total kidney GFR and superficial nephron GFR were determined in 42 Sprague Dawley rats after beta-adrenergic stimulation with isoprenaline and beta-adrenergic blockade with propranolol. Isoprenaline (0.3 g/kg · min i. v.) decreased urine volume, sodium and potassium excretion and increased urinary sodium and potassium concentration and urine osmolarity. These effects were reversed by injection of propranolol (2.2 mg/kg i.v.). Propranolol alone increased renal sodium and potassium excretion and urinary sodium concentration. Total kidney GFR did not change after both substances, whereas superficial nephron GFR increased after propranolol by 35% and decreased after isoprenaline by 35%. A redistribution of glomerular filtration rates among nephrons therefore must have occured with a shift of the GFR to deep nephrons after isoprenaline and to superficial nephrons after propranolol. The redistribution of glomerular filtration rates is thought to the related to the changes in urinary excretion of electrolytes. Additionally, isoprenaline increased fractional fluid reabsorption of superficial proximal convoluted tubules by 12.3%.