The effect of pelvic nerve stimulation on recto-anal motility in the cat

Rectal and anal motility responses to pharmacological manipulation of neuro-transmission and graded efferent electrical pelvic nerve stimulation were investigated in alpha-1-chloralose anaesthetized cats. N omega-nitro-L-arginine (L-NNA), a competitive inhibitor of nitric oxide synthase, did not influence spontaneous rectal and anal motility. No significant change in anal pressure or rectal tone was observed after sectioning the pelvic nerves in animals pretreated with L-NNA. The effect of pelvic nerve stimulation on anal tone was varying and depended upon the intensity of stimulation and the prevailing anal tone. A reduction of anal tone on pelvic nerve stimulation was consistently converted to an increase of anal tone after pretreatment with L-NNA. The rectal response to pelvic nerve stimulation was unchanged by L-NNA. Residual increase of anal tone observed on pelvic nerve stimulation after L-NNA and noradrenergic blockade was partly sensitive to hexamethonium and abolished by atropine. The results suggest that there is no tonic influence on rectal and anal motility via nitric oxide mechanisms. On the other hand, the reduction of anal tone on high intensity pelvic nerve stimulation seemed to be dependent on the release of nitric oxide. An excitatory cholinergic component of the smooth muscle contractility of the feline anal canal, partly sensitive to hexamethonium, was demonstrated to be conveyed in the pelvic nerves.