[Analgesic action of sodium diclofenac: behavioral and electrophysiological study in normal and polyarthritic rats]

In a behavioural study, the effects of intravenous diclofenac in a range of doses were determined by measuring vocalization thresholds to paw pressure in normal and Freund's adjuvant-induced arthritic rats. In normal rats, 6 and 9 mg/kg diclofenac produced an increase in vocalization thresholds (mean threshold values were respectively 135.67 +/- 3.30 per cent and 157.41 +/- 4.62 per cent of the control at 30 min; n = 9 for each group), no effect resulting with 3 mg/kg. In arthritic rats, 3, 6 and 9 mg/kg diclofenac induced a clear analgesic effect (mean threshold values being 172.22 +/- 4.26 per cent, 201.76 +/- 4.76 per cent and 222.33 +/- 5.10 per cent respectively of the control at 25 min, n = 9 for each group), no effect being observed with 1.5 mg/kg. An electrophysiological study performed on arthritic rats considered the effect of 6 mg/kg diclofenac upon the neuronal ventrobasal thalamic responses induced by mode-rate stimulation of an inflamed joint. The responses were depressed by about 50 per cent, 20 minutes after the injection. These results show that diclofenac displays a direct effect on pain processing; this effect is more potent in arthritic rats than in normal rats.