Elevated arterial pressure impairs autoregulation independently of AT(1) receptor activation.
OBJECTIVE
These studies determined the ability of AT1 receptor blockade or 'triple therapy', to reverse angiotensin II-induced hypertension and improve autoregulatory behavior.


METHODS
Experiments to determine if regulation of systolic blood pressure, in the normotensive range, would improve renal microvascular autoregulatory behavior in angiotensin II-infused rats.


METHODS
Hypertension was induced by chronic angiotensin II infusion (60 ng/min) for 10-14 days. Two groups of angiotensin II-infused rats received either AT1 receptor blockade, with candesartan cilexetil, or triple therapy, with hydralazine, hydrochlorothiazide and reserpine, beginning on day 6 or day 0 of angiotensin II infusion, respectively. Sham animals were studied as normotensive controls. Systolic blood pressure was measured by tail cuff. Autoregulatory behavior was assessed using the juxtamedullary nephron technique in response to step (15 mmHg) increases in perfusion pressure from 65 to 170 mmHg.


RESULTS
Angiotensin II infusion increased systolic blood pressure from a baseline of 125 mmHg to 162 and 182 mmHg after 10 and 14 days, respectively. Candesartan cilexetil and triple therapy normalized the blood pressure to between 119 and 126 mmHg. Increasing perfusion pressure, from 65 to 170 mmHg, reduced afferent arteriolar diameter by 30% in sham-treated kidneys. Autoregulation was significantly blunted in angiotensin II-infused rats, resulting in a pressure-mediated vasoconstriction of only 10%. Candesartan cilexetil, or triple therapy, significantly improved autoregulatory behavior, as indicated by pressure-mediated vasoconstrictor responses of 30 and 40%; respectively, despite continued angiotensin II infusion.


CONCLUSIONS
These data suggest that chronic elevation of arterial blood pressure, rather than chronic AT1 receptor stimulation, is sufficient to induce hypertensive impairment of renal autoregulatory capability.
Inscho
Edward W
EW
Department of Physiology and Vascular Biology Center, Medical College of Georgia, Augusta, Georgia 30912, USA. einscho@mail.mcg.edu
Cook
Anthony K
AK
Murzynowski
James B
JB
Imig
John D
JD
D000804:Angiotensin II / Q000494:pharmacology; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology / Q000627:therapeutic use; D001562:Benzimidazoles / Q000494:pharmacology; D001713:Biphenyl Compounds / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects*; D004359:Drug Therapy, Combination; D006706:Homeostasis / Q000187:drug effects*; D006830:Hydralazine / Q000627:therapeutic use; D006852:Hydrochlorothiazide / Q000627:therapeutic use; D006973:Hypertension / Q000139:chemically induced / Q000188:drug therapy*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism*; D012110:Reserpine / Q000627:therapeutic use; D013777:Tetrazoles / Q000494:pharmacology; D013997:Time Factors; D014661:Vasoconstriction; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D057911:Angiotensin Receptor Antagonists; D000959:Antihypertensive Agents; D001562:Benzimidazoles; D001713:Biphenyl Compounds; D044140:Receptor, Angiotensin, Type 1; D013777:Tetrazoles; D014662:Vasoconstrictor Agents; D006852:Hydrochlorothiazide; D000804:Angiotensin II; D006830:Hydralazine; D012110:Reserpine; C077793:candesartan cilexetil