EFFECT OF LOW AND HIGH CONCENTRATIONS OF ALFENTANIL ADMINISTERED INTRATHECALLY ON Aδ AND C FIBRE MEDIATED SOMATOSYMPATHETIC REFLEXES

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Abstract
We have studied the effects of alfentanil administered intrathecally on somatosympathetic reflexes evoked by stimulation of radial and tibial nerves in 10 anaesthetized and paralysed dogs. In five animals, alfentanil was administered in doses of 100, WO, 200 and 400 μ in 0.8 ml and 800 μ in 1.6 ml prepared from the formulation of 500 μ mt−1. Five others received alfentanil (high concentration formulation, 5 mg mf−1) in doses of 500 and 2000 μ in 0.5 ml and 5000 μ in 1 ml. C fibre tibial nerve reflexes were depressed by 100 μ and abolished with doses of 200–400 μ, but the Aδ response remained unaffected. Aδ responses were depressed also and abolished, respectively, by doses of alfentanil 2000μ and 5000 μ At the larger, but not the smaller, concentration there was evidence of baroreflex sensitization probably caused by systemic absorption of the drug.

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