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.
Department of Physiology and Biophysics, University of Alabama, Birmingham 35294.
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Mitchell
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Navar
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