The central effects of paraoxon on blood pressure of rabbits after intravenous administration or infusion via a vertebral artery.

In the present study paraoxon (28-825 micrograms/kg, i.v.) was administered into rabbits treated with N-methylatropine (1 mg/kg). In urethane-anaesthetized rabbits pressor and depressor effects were observed. In pentobarbitone-anaesthetized rabbits, however, only depresssor effects were noticed. Dexetimide (0.25-0.5 mg/kg) prevented the pressor and depressor action of paraoxon. Furthermore, paraoxon (83-825 micrograms) was infused into a vertebral artery of pentobarbitone-anaesthetized animals. After administration via this route the depressor effect was similar to i.v. administration. 30 min after administration of paraoxon acetylcholinesterase activity was determined in the medulla oblongata, the pons and the hypothalamus. The enzyme has to be inhibited almost completely to induce an effect on blood pressure. It is concluded that the vascular effects of paraoxon seem to be mediated by a mechanism involving stimulation of central muscarinic receptors, probably by accumulated acetylcholine, which in turn induces a decrease in blood pressure.