Effect of acute atenolol on short-term blood pressure variability and baroreflex sensitivity in rats

Beta-blocker therapy for hypertension or coronary artery disease is common, but there are a lot of controversies about its effects on short-term blood pressure variability and arterial baroreceptor reflexes. The aim of this study was to evaluate the effects of acute atenolol on baroreflex sensitivity (BRS) and on the spontaneous variability of systolic blood pressure (SBP) and RR intervals in conscious rats. Ten Wistar rats equipped with telemetry system were evaluated: 1) under control conditions; 2) after injection of saline; and 3) during beta1-adrenergic blockade by atenolol. Fast Fourier transform analysis was applied to RR intervals and SBP. Atenolol increased RR intervals significantly by 14% and the variation coefficient of the RR intervals by 31%. SBP was reduced significantly by 9%. In frequency domain, beta1-blockade in RR intervals increased very low frequency by 33% and the total power by 22% and decreased low frequency by 25%. The ratio of low to high frequency power decreased by 60%. Frequency domain variables in SBP were not significantly changed after beta1-adrenergic receptor blockade. BRS (gain alpha) was not significantly altered by beta-blockers. Acute atenolol decreased SBP and increased RR intervals with no change in BRS, indicating 'resetting' of baroreflex function.