Interaction between acetylcholine and bradykinin in the lateral septal area of the rat brain: involvement of muscarinic receptors in cardiovascular responses.

The lateral septal area was used as a model to study the interaction between acetylcholine (Ach) and bradykinin on arterial blood pressure, since both mediators are present in this region. In the lateral septal area, the administration of the peptide or Ach produced a long-lasting, sympathetic-mediated increase of arterial blood pressure which was blocked by atropine. Pretreatment of the lateral septal area with hemicholinium-3, which depletes stores of acetylcholine, partially blocked the pressor effect of bradykinin but not that of Ach. Captopril--an inhibitor of kininase II--enhanced the pressor effects of bradykinin and Ach. Synaptosomal studies showed that bradykinin increased sodium-dependent, high-affinity uptake of choline and the conversion of [3H]choline to [3H]acetylcholine. Competition experiments using the highly specific muscarinic antagonist [3H]quinuclidinyl benzilate, demonstrated that bradykinin displaced the muscarinic antagonist from its receptor-ligand complexes. These results suggest that in the lateral septal area acetylcholine and bradykinin interact in a positive feed-back which amplifies pressor responses.