The effects of electroacupuncture (Ea) on circulatory dynamics were investigated in anesthetized rats. The arterial blood pressure (BP) and the heart rate (HR) in response to Ea stimulations at the Tsusanli point (St-36) and the Hoku point (Li-4) were tested by a low frequency Ea (2 Hz; LFEa) and a high frequency Ea (20 Hz; HFEa) with stimulation intensities 20 times the motor threshold. Neither the HR nor the BP was affected when the Tsusanli point was stimulated. Whereas, Ea stimulations at the Hoku point elicit chronotropic and pressor effects. The patterns of pressor responses caused by the LFEa were different from that of an HFEa, i.e., the LFEa elicited a tonic effect, while an HFEa had a phasic one. The HFEa-induced pressor and chronotropic effects were attenuated, while the LFEa induced effects were completely blocked by an intravenous infusion of an alpha-adrenergic blocker (moxisylyte 0.2 mg/min/kg, i.v., for 20 min). A co-infusion with alpha-and beta-adrenergic blockers (propanolol 0.2 mg/min/kg, i.v., for 20 min) completely blocked the HFEa-induced pressor and chronotropic effects. We concluded that Ea stimulations, at the Hoku acupoint, with appropriate stimulation parameters can increase and maintain BP. Furthermore, the LFEa stimulation activates sympathetic vasomotor tone, whereas the HFEa stimulation causes an additional potentiation on the sympathetic drive to the heart.
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