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Cardiomegaly produced by chronic beta-adrenergic stimulation in the rat: comparison with alpha-adrenergic effects.
Authors:V T Pagano  M A Inchiosa
Institution:Department of Pharmacology, New York Medical College, Valhalla, N.Y. 10595, USA
Abstract:Chronic administration of d, l isoproterenol, 0.2 – 5 mg/kg/day, for 14–21 days in the male rat produced marked increases in dry ventricle weight (21.1 – 43.6%; p < 0.001). In comparison, an α-adrenergic agonist, phenylephrine (7.5 mg/kg/day) decreased ventricle weight (?15.3%; p < 0.025). Also, isoproterenol injection at 5 mg/kg/day decreased cardiac actomyosin ATPase activity by 23.3% (p < 0.0025) while phenylephrine, administered as above, did not influence ATPase activity. The effect of isoproterenol on heart weight was completely blocked by the β1-adrenergic antagonist practolol (5 mg/kg/day). Albuterol, a relatively specific β2-adrenergic agonist was less potent than isoproterenol in producing cardiac hypertrophy. l-Epinephrine injection, 0.8 mg/kg/day for 14 days, had no effect on heart weight. However, l-epinephrine produced cardiac hypertrophy (22.4% p < 0.001) when the animals were preinjected with the α-adrenergic antagonist, phenoxybenzamine (5 mg/kg/day). The data indicate that cardiac hypertrophy can be produced by stimulation of the β1-adrenergic receptors of the heart; apparently, stimulation of α-adrenergic receptors opposes β-adrenergic hypertrophic effects.
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