Enhanced tubuloglomerular feedback during peritubular infusions of angiotensins I and II.
Experiments were performed in pentobarbital sodium-anesthetized rats to determine whether increases in intrarenal generation of angiotensin II (ANG II) can enhance the sensitivity of the tubuloglomerular feedback mechanism. Stop-flow pressure (SFP) feedback responses to step increases in late proximal perfusion rate were obtained during control conditions and during simultaneous peritubular capillary infusion of either angiotensin I (ANG I) or ANG II. Infusion of either 10(-7) M ANG II or 10(-5) M ANG I, at rates (18.3 +/- 0.9 and 14.8 +/- 1.5 nl/min, respectively) that did not affect resting SFP, enhanced the magnitude of SFP feedback responses both at a low proximal perfusion rate of 10 nl/min (2.9 +/- 0.9 vs. 0.3 +/- 0.2 and 4.5 +/- 1.0 vs. 0.1 +/- 0.1 mmHg, respectively) and at proximal perfusion rates (greater than 30 nl/min) that elicited a maximal feedback response (13.1 +/- 1.0 vs. 10.1 +/- 0.7 and 13.5 +/- 1.6 vs. 9.8 +/- 0.8 mmHg, respectively). With a higher ANG I infusion rate (20 nl/min), control SFP measured in the absence of distal volume delivery decreased from 39.2 +/- 0.6 to 12.0 +/- 2.8 mmHg (n = 18). These effects were blocked when the ANG II receptor antagonist, saralasin (10(-5) M, Sar), was added to the infusate. In addition, the magnitude of the maximal SFP feedback response was not altered during infusion of Sar alone or ANG I + Sar. These findings indicate that ANG II, either added or formed de novo beyond the glomerular circulation, can enhance the sensitivity of the tubuloglomerular feedback mechanism.
Mitchell
K D
KD
Department of Physiology and Biophysics, University of Alabama, Birmingham 35294.
Navar
L G
LG
D000803:Angiotensin I / Q000494:pharmacology*; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002196:Capillaries / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005246:Feedback; D007678:Kidney Glomerulus / Q000187:drug effects / Q000502:physiology*; D007684:Kidney Tubules / Q000098:blood supply / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values
D000804:Angiotensin II; D000803:Angiotensin I