Lethal effect of the serotonin-xylocaineR association in ganglion-blocked rats

In rats anestetized with urethane and under ganglionic blockade by hexamethonium (20 mg/kg, i.v.), the i.v. injection of serotonin (60 mug/kg) determined apnea, ECG alterations and a brief hypotensive response which is similar to that as elicited when 5-HT is given to intact rats. During the hypertension which follows that initial response, apnea is still present along with more severe ECG changes. After that, blood pressure falls into a prolonged hypotension, which is invariably accompanied by death. Neither norepinephrine, nor respiratory analeptics (CoramineR, RemeflinF) were able to prevent the fatal outcome. Only artificial respiration was found to be useful in some instances. It was concluded that the association serotonin plus lidocaine becomes lethal when given to ganglion-blocked rate, and this toxic effect can be ascribed mainly to the respiratory depressor activity of the drugs.