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Renal Research Group, Medical Department A, University of Bergen, N-5021 Bergen, Norway
The relationship
between systemic blood pressure and glomerular capillary pressure
(Pgc) in
spontaneously hypertensive rats (SHR) during treatment with
antihypertensive drugs is still unclear. The effects of an
angiotensin-converting enzyme inhibitor (enalapril), two calcium
channel antagonists (nifedipine and verapamil), and an
1-receptor blocker (doxazosin)
on renal blood flow (RBF) autoregulation, Pgc, and renal segmental
resistances were therefore studied in SHR. Recordings of RBF
autoregulation were done before and 30 min after intravenous infusion
of the different drugs, and Pgc was thereafter measured with the stop-flow technique. When the mean
arterial pressure (MAP) was reduced to ~120 mmHg by infusions of
doxazosin or enalapril, the lower pressure limit of RBF autoregulation was reduced significantly. Nifedipine or verapamil abolished RBF autoregulation. Doxazosin did not change
Pgc (43.6 ± 1.4 vs. 46.7 ± 1.5 mmHg in controls, P > 0.5),
enalapril lowered (41.3 ± 0.8 mmHg,
P < 0.01), and the calcium channel
antagonists increased Pgc
[53.7 ± 1.4 mmHg (nifedipine) and 54.8 ± 1.2 mmHg
(verapamil), P < 0.01]. When
MAP was reduced to ~85 mmHg by drugs,
Pgc was reduced to 43.3 ± 1.7 mmHg after nifedipine (P > 0.2 vs.
control), whereas Pgc after
enalapril was 38.5 ± 0.5 mmHg
(P < 0.05 vs. control).
Enalapril reduced Pgc mainly by
reducing efferent resistance. During treatment with calcium channel
antagonists, Pgc became strictly
dependent on MAP. Monotherapy with nifedipine may increase Pgc and by this mechanism
accelerate glomerulosclerosis if a strict blood pressure control is not
obtained.
calcium channel antagonist; angiotensin-converting enzyme
inhibitor;
1-adrenergic
receptor blocker; hypertension; renal micropuncture; renal
hemodynamics; renal blood flow
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