Excitatory and Inhibitory Influence of Pathways in the Pelvic Nerve on Bladder Activity in Rats with Bladder Outlet Obstruction.

OBJECTIVES

This study was undertaken to investigate whether chronic bladder outlet obstruction (BOO) in female rats influences the tonic parasympathetic excitatory or inhibitory reflex control of bladder activity. METHODS: Bladder activity during isovolumetric cystometry (1.5-12 mL) was examined after transection of dorsal and ventral lumbosacral spinal roots (L4-S4) and administration of hexamethonium, a ganglionic blocking agent, in urethane anesthetized female rats with sympathectomy and BOO. RESULTS: Lumbosacral dorsal root transection abolished reflex bladder contractions, but did not influence intravesical baseline pressure. However, ventral root transection after dorsal root transection decreased baseline intravesical pressure (y: % change) at low bladder volumes (x) and increased pressure at high volumes. The calculated (y = 1.9x - 16.5) transition volume was 9 mL. Administration of hexamethonium (100 mg/kg, intraperitoneally) after dorsal and ventral root transection increased the amplitude and decreased the frequency of myogenic bladder contractions. CONCLUSION: The bladder is tonically excited or inhibited depending upon bladder volume by the interactions between a parasympathetic preganglionic pathway in the pelvic nerve and a peripheral reflex. However, in rats with BOO, the volume at which the response shifts from excitation to inhibition was very large, and tonic function of the parasympathetic preganglionic pathway was weak compared to previously reported results in rats without BOO. The persistence of reflex tonic excitatory control of bladder tone over a broad range of bladder volumes may be one of the reasons for overactivity of the bladder with outlet obstruction.