PREGNANCY ENHANCES THE ANTINOCICEPTIVE EFFECTS OF EXTRADURAL LIGNOCAINE IN THE RAT

We have compared the antinociceptive effect of extradural lignocaine o n somatic and visceral nociception in pregnant (n = 11) and non-pregna nt rats (n = 9). Colorectal distension (CD) threshold and tail flick ( TF) latency were measured as visceral and somatic nociception, respect ively for 60 min after extradural injection. On days 19, 20 and 21 of pregnancy, rats received lignocaine 200, 400 or 800 mu g or normal sal ine via a chronically implanted lumbar extradural catheter. Extradural lignocaine produced dose-dependent antinociceptive effects on TF late ncy and CD threshold. Lignocaine 200 or 400 mu g produced significantl y greater peak effects in pregnant than in non-pregnant rats. Although the peak effects with lignocaine 800 mu g were not different between groups, the duration of the effects were longer in pregnant compared w ith nonpregnant rats. We conclude that both somatic and visceral antin ociceptive effects of extradural lignocaine were potentiated in pregna nt rats near term compared with those in non-pregnant rats.