Micturition in rats: a chronic model for study of bladder function and effect of anesthetics

The volume-evoked micturition reflex (VEMR) and the effects of anesthetics on the VEMR were studied in a chronic unanesthetized rat model. The bladder catheter was implanted chronically through a laparotomy and externalized percutaneously. An intrathecal (IT) catheter was implanted chronically in animals scheduled for an IT injection. By 2 days after implantation, infusion of saline (200 microliter/min) in the bladder reliably resulted in a low base-line pressure (BP) followed by a transient increase in bladder pressure, an opening of the sphincter (bladder opening pressure, BOP) corresponding to expression of urine (volume of urination, V), then a further rise in pressure (peak pressure, PP) and a subsequent return to base line. Seven days after implantation, values (means +/- SE) for BP, BOP, PP, and V were 10 +/- 0.3, 30 +/- 2, 67 +/- 6 cmH2O, and 1.0 +/- 0.1 ml, respectively. Residual volumes were reliably less than 2-4% of the expressed volume. The VEMR was reliably evoked up to 28 days after implantation. V values in unimplanted and implanted animals were not different. In implanted animals, VEMR parameters were not different during infusion or during spontaneous urination after oral fluid load. Administration of pentobarbital sodium (50 mg/kg ip), alpha-chloralose (130 mg/kg ip), ketamine (100 mg/kg im), halothane (in air 2%), and local anesthetics (2-chloroprocaine 3% or bupivacaine 0.75%, 10 microliter IT) produced a complete blockade of the VEMR and overflow incontinence at pressures significantly higher than BOP values. To compare overflow pressures and passive compliance of the bladder, unanesthetized animals were decapitated.(ABSTRACT TRUNCATED AT 250 WORDS)