Selective effect of sufentanil on group III (A delta) and group IV (C) somatosympathetic reflexes

The effect of sufentanil on somatosympathetic reflexes and the subsequent reversal of its effects by naloxone have been observed in dogs anaesthetised with alpha-chloralose, paralysed with suxamethonium and artificially ventilated. When the drug was infused at a rate of 2.5 micrograms kg-1 min-1 the late long latency response evoked by Group IV (C) fibres was totally abolished at a mean dose of 6.40 micrograms kg-1 (+/- 0.99 microgram kg-1) (s.e. mean), while retaining a substantial part of the early short latency response evoked by group III (A delta) fibres; subsequently, during the infusion, this response was also totally abolished at a mean dose of 26.2 micrograms kg-1 (+/- 3.2 mg kg-1). The administration of naloxone (2 mg i.v.) completely reversed the effects of sufentanil within 3-5 min in different preparations. Some of the implications of these results are discussed.