Effect of catecholamines on fluid reabsorption by the isolated proximal convoluted tubule

The effect of L-norepinephrine and isoproterenol on fluid transport was studied in superficial convoluted segments and straight portions of the rabbit proximal tubule (PCT and PR, respectively) by the technique of microperfusion in vitro. In PCT, L-norepinephrine (10(-6) M) added to the bath stimulated reversibly fluid reabsorption (Jv) by about 67%. In the presence of propranolol (10(-4) M) in the bath, L-norepinephrine caused a small (about 19%) but significant decrease of Jv. Phentolamine and isoproterenol added simultaneously to the bath also increased fluid reabsorption, an effect that was abolished by propranolol. Norepinephrine had no effect on Jv when added to the perfusate in PCT. No change of Jv was observed after addition of norepinephrine to the bath in PR. The effects on fluid reabsorption rate observed in PCT are consistent with a physiologic role of the sympathetic nervous system in the modulation of PCT fluid transport.