EFFECT OF DITERPENOID ALKALOIDS ON CARDIAC SYMPATHETIC EFFERENT AND VAGAL AFFERENT NERVE ACTIVITY

The diterpenoid alkaloid, lappaconitine, at a dose of 150 mu g/kg (i.v .) increased cardiac vagal afferent nerve activity (16.2%) and reduced cardiac sympathetic efferent nerve activity (12.5%). A polar analog, N-deacetyllappaconitine, at this same dose, increased cardiac vagal af ferent nerve activity (40%) and reduced cardiac sympathetic efferent n erve activity (23.5%). Both of these agents also reduced arterial bloo d pressure and heart rate. A larger dose of lappaconitine (300 mu g/kg i.v.) produced the same changes in nerve activities and cardiac funct ion as the lower dose. Two other structurally related agents, lycocton ine and aconine, failed to alter these variables in doses up to 300 mu g/kg. These data suggest that certain diterpenoid alkaloids activate autonomic reflex receptors, including cardiac reflex receptors. The po lar agent, N-deacetyllappaconitine, appears to be more effective on ca rdiac reflex receptors than the non-polar agent, lappaconitine. Such a gents may be useful in the treatment of hypertension.