EVALUATION OF THE ANTINOCICEPTIVE EFFECT OF XYLAZINE AFTER LUMBOSACRAL INJECTION IN DOGS ANESTHETIZED WITH ISOFLURANE

Seven dogs anaesthetized with isoflurane in oxygen (1.9 Vol.-% ET) wer e examined before and after lumbosacral injection of xylazine (0.25 mg /kg) into the epidural space. Over a 240 minute period the dogs were f irst stimulated in a visceral manner (extension of the colon descenden s by a balloon-catheter) every 15 minutes. Tn a second part, the dogs were stimulated somatically by pressure to the interdigital skin of a hindlimb. Heart rate and mean arterial pressure were used to determine the analgesic properties of epidurally injected xylazine. Furthermore , plasma xylazine concentration was controlled in both series. Before epidural anaesthesia, heart rate and mean arterial pressure increased during stimulation significantly in both groups. After epidural inject ion of xylazine, hemodynamic reactions were distinctly diminished, in the somatically stimulated group more than in the viscerally stimulate d group. Up to 30 minutes after epidural injection, plasma xylazine co ncentrations of about 100 ng/ml were found in both groups. Up to 60 mi nutes after epidural injection, plasma xylazine concentrations of more than 60 ng/ml still were found. From the 120th minute on, xylazine co ncentration decreased below 30 ng/ml. From these results, it can be co ncluded that there is a well-suited analgesic effect of epidurally app licated xylazine for approximately 240 minutes.