Adrenergic influences on the spinal cardiovascular neurones.

In cervical spinal cord transected and bilaterally vagotomized dogs, intrathecal (i.t.) injection of clonidine decreased the resting heart rate and mean arterial pressure (MAP) while isoprenaline increased the heart rate. The clonidine induced bradycardia and hypotension were antagonized by piperoxan pretreatment. Similarly, the isoprenaline induced tachycardia was antagonized by pretreatment (i.t.) with atenolol. Intrathecal atenolol per se decreased the heart rate and MAP while piperoxan had no effect. The post-coronary artery ligation cardiac arrhythmia, in the cervical spinal cord transected and bilaterally vagotomized dogs, was inhibited by clonidine, phenylephrine and methoxamine and facilitated by isoprenaline. beta-Adrenoreceptor antagonists propranolol, atenolol and acebutolol, given intrathecally, inhibited while piperoxan facilitated the cardiac arrhythmia. The clonidine and isoprenaline induced changes in the arrhythmia were antagonized by i.t. pretreatment with piperoxan and atenolol respectively. It appears that the alpha-adrenoreceptors are inhibitory while beta-adrenoreceptors are facilitatory for spinal control of heart rate and blood pressure and for post-coronary artery ligation cardiac arrhythmia.