Effect of alpha 1-adrenoceptor blockade on the left ventricular force-length relationship in dogs.
We used the left ventricular (LV) end-systolic force-diameter (Fes-Des) relation to evaluate the effect of an alpha1-adrenoceptor antagonist (bunazosin hydrochloride) on the contractility of the beta-blocked left ventricle. Nine adult mongrel dogs were instrumented with ultrasonic crystals to measure LV diameter and a micromanometer to measure LV pressure. Beta-adrenergic and vagal blockade was induced with intravenous propranolol (2 mg/kg) and atropine (0.2 mg/kg), respectively, and preload was decreased by inferior vena caval occlusion. The slope (Ec) and extrapolated diameter intercept (Do) of the LV Fes-Des relation were derived from end-systolic data obtained in the control state (after beta-blockade) and after bunazosin infusion (1 mg/kg). Ec was used as a new index of LV contractility. After bunazosin infusion, the heart rate and Ec were decreased by 7 and 22%, respectively, in comparison with the control state, whereas Do did not change. These results indicate that alpha1-adrenoceptor blockade significantly reduces myocardial contractility in the beta-blocked canine heart, perhaps by decreasing the intracellular calcium concentration and/or myosin ATPase activity.
Takeda
K
K
Department of Medicine, Dokkyo University School of Medicine, Tochigi, Japan.
Shimizu
T
T
Nakamura
Y
Y
Masuda
T
T
Kono
K
K
Takahashi
M
M
Oyama
M
M
Yagi
S
S
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004285:Dogs; D009200:Myocardial Contraction / Q000187:drug effects*; D011799:Quinazolines / Q000494:pharmacology*; D012044:Regression Analysis; D016277:Ventricular Function, Left / Q000187:drug effects*
D000317:Adrenergic alpha-Antagonists; D011799:Quinazolines; C018176:bunazosin