Daily exercise attenuated the sympathetic component of the spontaneous arterial baroreflex control of heart rate in hypertensive rats

The influence of daily spontaneous running on the sympathetic and parasympa thetic components of the spontaneous arterial baroreflex control of heart r ate was examined in 22 female spontaneously hypertensive rats [12 sedentary and 10 daily spontaneous running]. Following 8 weeks of sedentary control or daily spontaneous running, animals were chronically instrumented with an arterial catheter. Daily spontaneous running resulted in an increased hear t weight/body weight ratio (5.2+/-0.27 vs 4.3+/-0.01 g/kg) and a resting br adycardia (321+/-8 bpm vs 360+/-6). The spontaneous changes in arterial pre ssure and the reflex responses of heart rate were examined under three expe rimental conditions: 1) pre-blockade, 2) following beta(1)-adrenergic recep tor blockade, and 3) following muscarinic-cholinergic receptor blockade. Da ily spontaneous running attenuated the spontaneous gain of the arterial bar oreflex control of heart rate (56%). After muscarinic-cholinergic receptor blockade, the spontaneous gain remained reduced in daily spontaneous runnin g rats (57%). In contrast, after beta(1)-adrenergic receptor blockade the s pontaneous gain was not different between sedentary control and daily spont aneous running animals. Results demonstrate that daily spontaneous running decreased the sympathetic component resulting in an apparently greater infl uence of the parasympathetic component on the spontaneous arterial barorefl ex control of heart rate.