Characterization of pressor and visceromotor reflex responses to bladder distention in rats: Sources of variability and effect of analgesics

Purpose: We assessed the usefulness of cardiovascular and visceromotor resp onses to bladder distention as measures of acute visceral nociception in ra ts by determining the reliability of these responses. Materials and Methods: Halothane anesthetized male and female Sprague-Dawle y rats were acutely instrumented with tracheal, jugular venous, carotid art erial. and bladder cannulas. Wires were inserted into the abdominal muscula ture to enable myoelectrical activity measurement. Anesthesia was decreased until flexion reflexes were present. Repeat phasic and graded bladder dist ention was administered, and arterial blood pressure and abdominal electrom yography activity were continuously monitored. We determined the effects of gender, vaginal smear estrous cycle stage and drug treatment on the measur ed responses. Results: Bladder distention produced reliable presser and visceromotor (abd ominal contractile) responses. There was great inter-animal variability in response vigor but good reproducibility was noted within individual animals . During slow bladder filling bladder contractions were not noted at this l evel of anesthesia. Sex differences included a more vigorous reflex respons e in females than in males, which was most vigorous in females in proestrus . Repeat bladder distention led to increasingly vigorous presser responses and the improved reliability of visceromotor responses. Intravenous morphin e and lidocaine dose dependently inhibited the reflex responses. Conclusions: Presser and visceromotor responses to bladder distention in ha lothane anesthetized rats are reliable measures of acute bladder nociceptio n that may prove useful for analgesic screening and in studies of hormonal effects on nociception.