DISSOCIATION BETWEEN THE EFFECT OF NITROUS-OXIDE ON SPONTANEOUS AND REFLEXIVLY EVOKED SYMPATHETIC ACTIVITY IN DOGS

We have examined the effect of nitrous oxide on spontaneous sympatheti c activity and A delta- and C-fibre mediated somatosympathetic reflexe s in renal nerves, evoked by supramaximal electrical stimulation of ra dial nerves in anaesthetized, paralysed dogs undergoing mechanical ven tilation. In six preparations, nitrous oxide was administered at end-t idal concentrations of 10%, 30%, 50% and 70%, each for 20 min. Spontan eous renal sympathetic activity increased significantly to 147.8% and 151.2% of control values with 50% and 70% nitrous oxide, respectively (P<0.05), but there were no significant changes in A delta and C refle xes. We conclude that the large increase in spontaneous sympathetic ac tivity was dissociated from somatosympathetic reflexes which remained unchanged at these concentrations of nitrous oxide.