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1 Division of Cardiovascular Disease, Department of Medicine, 2 Birmingham Veterans Affairs Medical Center, and 3 Department of Pathology, University of Alabama, Birmingham 35294; 4 Auburn University College of Veterinary Medicine, Auburn, Alabama 36849; 5 Emory University, Atlanta, Georgia 30322; and 6 Medical University of South Carolina, Charleston, South Carolina 29425
We studied the gradual onset of
pressure overload (PO) induced by a mildly constricting aortic band in
8-wk-old puppies (n = 8) that increased to 98 ± 11 mmHg at 9 mo. Left ventricular (LV) weight/body weight was increased
in PO versus sham-operated littermate controls [8.11 ± 0.60 (SE)
vs. 4.46 ± 0.38 g/kg, P < 0.001]. LV
end-diastolic diameter, diastolic pressure, and fractional shortening
did not differ in PO versus control dogs. There were no inducible
arrhythmias in response to an aggressive electrophysiological stimulation protocol in PO dogs. Furthermore, isolated cardiomyocyte function did not differ between control and PO dogs. LV angiotensin II
(ANG II) levels were increased (68 ± 12 vs. 20 ± 5 pg/g,
P < 0.01) as steady-state ANG II type 1 (AT1) receptor mRNA was decreased 40% and endothelial
nitric oxide synthase mRNA levels were increased 2.5-fold in PO versus
control dogs (P < 0.05). Total ANG II receptor binding
sites of freshly prepared cardiac membranes demonstrated no difference
in the dissociation constant, but there was a 60% decrease in maximum
binding (Bmax) in PO versus control dogs (P < 0.01). LV ANG II levels correlated negatively with AT1
receptor mRNA levels (r =
0.75, P < 0.01) and total AT1 receptor Bmax
(r =
0.77, P < 0.02). These results
suggest that LV ANG II negatively regulates AT1 receptor
expression and that this is an adaptive response to chronic PO before
the onset of myocardial failure in the young dog.
angiotensin II; hypertrophy; angiotensin II receptors; arrhythmias
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