Bradycardic responses to vagal stimulation and methacholine injection in sinoaortic denervated rats

The bradycardia that occurs in response to vagal stimulation or to methacholine after 6 h of sinoaortic denervation (SAD) was studied in SAD rats before and after adrenergic blockade to determine whether the peripheral vagal action was impaired by sympathetic hyperactivity. A marked attenuation in the responses to methacholine and no difference in the responses to vagal stimulation were observed in SAD rats compared to sham-operated controls. The adrenergic blockade attenuated the responses to both vagal stimulation and methacholine in control rats but not in SAD rats. These findings revealed an impairment of peripheral vagal function after 6 h of SAD, probably due to a decreased sensitivity of the muscarinic receptors.