Left Ventricular Performance in Spontaneously Hypertensive Rats After Chronic β1-Adrenoceptor Blockade with Atenolol

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Abstract
We evaluated the role of chronic cardioselective β-adrenoceptor blockade in left ventricular (LV) function in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Commencing at 4 weeks of age, the animals were injected twice daily (20 mg/kg) with atenolol and were studied at either 10 or 16 weeks of age, to compare the stages of developing and established hypertension in SHR. Both blood pressure and LV mass were attenuated in the treated SHR. Ventricular function—evaluated by increasing preload (infusion of Tyrode solution) and recording indices of peak cardiac output, i.e., cardiac index (CI), stroke index (SI), and acceleration of flow—was similar in SHR and WKY at both 10 and 16 weeks of age. At 10 weeks, peak CI and SI were not significantly different in treated and non-treated SHR. By 16 weeks, however, atenolol treatment was associated with a significant decrease in peak CI (20%) attributable mainly to a lower SI. LV end-diastolic and systolic pressures were not affected by chronic treatment with the β-adrenoceptor antagonist. It is concluded that, when prolonged atenolol treatment is initiated during early postnatal life, peak LV function in SHR is compromised.