NITROUS-OXIDE DEPRESSES SOMATOCARDIAC SYMPATHETIC A-REFLEXES AND C-REFLEXES IN ANESTHETIZED RATS

Effect of nitrous oxide (N2O) on the somatosympathetic A- and C-reflex es was investigated using artificially ventilated rats anesthetized wi th alpha-chloralose and urethane. Somatocardiac sympathetic A- and C-r eflexes were elicited in the inferior cardiac nerve by electrical stim ulation of A and C afferent fibers of the tibial nerve, respectively. Both reflexes were depressed by inhalation of N2O for 20 min. The depr ession was greater in the C-reflex than in the A-reflex. The depressiv e effects of N2O on both reflexes were unchanged after pretreatment wi th intravenous naloxone (0.2 or 2.0 mg/kg) or by prolongation of the i nhalation of N2O for 2 h. These results suggest that the opioid recept or is not involved and that acute tolerance is not developed in the de pressive action of N2O on the somatosympathetic A- and C-reflexes.