title: The role of the kidney in canine blood pressure control: direct assessment of the closed-loop gain.
abstract: 1. The feedback control of arterial blood pressure by the kidney in the range of hours was investigated in resting, conscious foxhounds. 2. A servo-control device (connected to an aortic occlusive cuff implanted above both renal arteries) was used to maintain a constant pressure difference of 20 mmHg between aortic pressure measured proximal (mean arterial blood pressure: MAP) and distal (renal artery pressure: RAP) to the aortic cuff. 3. Protocol 1 (n = 6) served as a 4 h time control without intervention, protocol 2 (n = 6) consisted of three periods: after a control of 20 min duration, the servo-control device was activated for 180 min; this was followed by a recovery period of 40 min. Protocol 3 (n = 6) was as protocol 2, but during converting-enzyme inhibition. 4. Servo-control increased plasma renin activity (PRA) transiently from 0.5 ng angiotensin I (AI) ml-1 h-1 to a peak value of 2.4 ng AI ml-1 h-1, subsequently both RAP and MAP rose to reach a new steady state. During this increase in RAP, PRA declined to 1.4 ng AI ml-1 h-1. 5. On average, the compensation of the pressure decrease sensed by the kidney amounted to 63% of the error signal (closed-loop gain of 0.63 +/- 0.1). 6. Converting-enzyme inhibition reduced this closed-loop gain significantly (protocol 2 vs. protocol 3, 0.63 +/- 0.1 vs. 0.15 +/- 0.1; P < 0.05). 7. It is concluded, that the kidney plays an important role in medium-term blood pressure regulation, most probably via the renin-angiotensin system.
authors.affiliation: I. Physiologisches Institut der Ruprecht-Karls Universität Heidelberg, FRG.
authors.forename: P B
authors.initials: PB
authors.lastname: Persson
authors.forename: H
authors.initials: H
authors.lastname: Ehmke
authors.forename: H R
authors.initials: HR
authors.lastname: Kirchheim
authors.forename: M
authors.initials: M
authors.lastname: Lempinen
authors.forename: B
authors.initials: B
authors.lastname: Nafz
mesh_terms: D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D004285:Dogs; D004867:Equipment Design; D004864:Equipment and Supplies; D005246:Feedback; D005260:Female; D007668:Kidney / Q000502:physiology*; D008297:Male; D010827:Physiology / Q000295:instrumentation; D017257:Ramipril / Q000494:pharmacology; D012077:Renal Artery / Q000502:physiology; D012083:Renin / Q000097:blood
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D012083:Renin; D017257:Ramipril