To assess the protective effect of an alpha 1-blocker on the development of
cardiac hypertrophy, the selective alpha 1-receptor antagonist
bunazosin (2 mg/kg/d, by oral gavage and in
drinking water) was given to male Dahl salt-sensitive rats fed a 4% NaCl diet for 7 weeks. Control animals received water only by the same method. Treatment with
bunazosin was started when the animals were 7 weeks of age. Blood pressure, pulse rates, and
body weight were measured every week during the experiment. Urine was collected for 24 h on the final day of the experiment. All animals were killed by
decapitation, blood was collected, and the heart was removed. In both the treated and control groups, time-dependent increase in blood pressure and
body weight were observed, and there were no significant differences between the groups in blood pressure or
body weight during the experiment. Pulse rate remained unchanged in both groups throughout the experiment. The left ventricular
weight/body weight ratio and the left ventricular tissue
DNA content were significantly lower in the rats receiving
bunazosin than in the control rats. Plasma
renin activity, plasma
aldosterone, and plasma
atrial natriuretic peptide did not differ significantly between the two groups. No significant differences in glomerular filtration rate, urine volume,
sodium excretion, urinary
metanephrine excretion, and urinary
normetanephrine excretion were noted between the two groups. The results indicate that a sub-
antihypertensive dose of
bunazosin can inhibit the development of
cardiac hypertrophy without suppression of the pressure load, suggesting an important role of alpha 1-adrenergic receptors in the pathogenesis of
cardiac hypertrophy following the development of
hypertension.