DISSOCIATION OF TUBULOGLOMERULAR FEEDBACK RESPONSES FROM DISTAL TUBULAR CHLORIDE CONCENTRATION IN THE RAT

Previous studies demonstrated that stop-flow pressure (SFP) feedback responses can occur during orthograde perfusion with solutions having low amounts of sodium or chloride. Retrograde perfusion studies suggested a specific role for chloride concentration in mediating feedback responses. Here, SFP feedback responses were compared during orthograde and retrograde perfusion with an artifical tubular fluid solution (ATF) (Cl- = 135 meq/l) and a Na+ isethionate solution (Cl- = 6 meq/l). With ATF, increases in perfusion rate from 10 to 35 nl/min led to decreases in SFP of 11 .+-. 1.4 mmHg, increases in distal tubular fluid Cl- of 46 .+-. 4.9 meq/l and osomolality of 58 .+-. 10 mosmol/kg. There were significant inverse relationships between SFP and changes in Cl- and osmolality. With Na+ isethionate, SFP decreased by 8.4 .+-. 1.0 mmHg, osmolality increased by 43 .+-. 8 mosmol/kg and Cl- did not change. There was a significant relationship between SFP and osmolality, but not with Cl-. During retrograde perfusion at 15 nl/min, SFP decreased by 12 .+-. 1.2 mmHg with ATF and by 12 .+-. 1.2 mmHg with Na+ isethionate. Feedback-mediated decreases in SFP can occur in the absence of concomitant increases in distal Cl-; the receptor system evidently does not have a unique and specific requirement for chloride.