Effect on cardiac sympathetic nerve activity of phenylephrine microinjected into the cat intermediolateral cell column.

1. In anaesthetized cats the effect of the alpha 1-adrenoceptor agonist phenylephrine, microinjected into the left intermediolateral cell column of the spinal cord at the third thoracic level, was studied on left inferior cardiac nerve activity. 2. Microinjection of 100 nl of 10 or 40 mM-phenylephrine caused increases in inferior cardiac nerve activity in fifteen out of seventeen experiments. 3. The microinjection of the alpha 1-adrenoceptor antagonist alfuzosin (100 nl of 10 mM) into the intermediolateral cell column antagonized the excitatory response elicited by phenylephrine. 4. Increases in inferior cardiac nerve activity produced by glutamate and 5-hydroxytryptamine microinjected into the intermediolateral cell column were not antagonized by alfuzosin. 5. It is concluded that activation of alpha 1-adrenoceptors in the region of the intermediolateral cell column can cause an increase in the firing rate of sympathetic preganglionic neurones which innervate postganglionic neurones projecting into the inferior cardiac nerve.