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Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112
Chronic infusions of initially
subpressor doses of angiotensin II (ANG II) lead to progressive
hypertension over a 2-wk period and to augmented intrarenal ANG II
levels. The present study was performed to investigate total renal
blood flow (RBF) and medullary blood flow (MBF) autoregulatory behavior
and pressure-natriuresis in ANG II-infused hypertensive rats and how
these are modified by concomitant treatment with an ANG II
AT1 receptor antagonist. ANG II-infused rats
(n = 27) were prepared by administration of ANG II at
60 ng/min via osmotic minipump for 13 days. Twelve of the ANG
II-infused hypertensive rats were treated with losartan in the drinking
water (30 mg · kg ·
1 day
1).
Rats were anesthetized with pentobarbital sodium (50 mg/kg, ip) and
prepared for renal function measurements. An aortic clamp was placed
above the junction of the left renal artery to reduce renal arterial
pressure. Autoregulatory responses for renal plasma flow, overall RBF,
and glomerular filtration rate were impaired in ANG II-infused
hypertensive rats; however, MBF autoregulation was not disrupted. Most
strikingly, pressure-natriuresis was markedly suppressed in ANG
II-infused hypertensive rats. Chronic treatment with losartan prevented
the impairment of the pressure-natriuresis relationship caused by
chronic ANG II infusion. These findings demonstrate that chronic ANG II
infusion leads to marked impairment of sodium excretion and suppression
of the pressure-natriuresis relationship, which may contribute to the
progressive hypertension that occurs in this model. These renal effects
are prevented by simultaneous treatment with an AT1
receptor blocker.
autoregulation; glomerular filtration rate; renal blood flow; medullary blood flow; sodium excretion; angiotensin II
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