Effects of exercise and beta-blocker on blood pressure and baroreflexes in spontaneously hypertensive rats.

BACKGROUND: Exercise training or beta-blocker decreases high blood pressure (BP) and improves abnormal baroreflex function associated with hypertension. This study was undertaken to examine whether the effects of exercise training are additive to beta-blocker in spontaneously hypertensive rats (SHR).
METHODS: At 5 weeks of age, SHR were allocated to four groups: sedentary control, exercise training, treatment with moderate dose of bisoprolol, and their combination. Systolic BP was monitored by the tail-cuff method under restrained conditions. Sigmoidal mean arterial pressure (MAP)-heart rate (HR) reflex curves were obtained in rats at 17 weeks of age under quiet conditions before and after atenolol to ensure sympathetic blockade and to determine the vagal component of gain. After studying baroreflex function, intrinsic HR was obtained by additional administration of atropine.
RESULTS: Before atenolol, both exercise training alone and bisoprolol alone lowered resting MAP and HR, and decreased upper plateau (maximal tachycardia) and lower plateau (maximal bradycardia), resulting in decreased sympathetic component of HR range (upper plateau - intrinsic HR) and increased vagal component of HR range (intrinsic HR - lower plateau). After atenolol, both exercise training alone and bisoprolol alone increased the gain of vagal component. Exercise training had no additive effect on any parameters to bisoprolol except for systolic BP and HR measured by the tail-cuff method.
CONCLUSIONS: Exercise training and bisoprolol have similar effects concerning resting hemodynamics and baroreflex function in SHR. Although additive effects of exercise training to bisoprolol are not evident under quiet, nonstressful conditions, some additive effects may be obtained under stress such as restrain.