Pelvic floor muscles response to graded rectal distension and cutaneous stimulation.

The responses of the external ani sphincter (EAS) and the levator ani (LA) muscles to graded rectal distension and to cutaneous and genital stimulation were examined in 25 cats of either sex. The animals were anesthetized with sodium pentobarbital (30 mg/kg, intraperitoneal) and then tested in two positions: with hindlimbs extended and with hindlimbs flexed simulating the straining position. Graded rectal distension was performed at two speeds: 1 and 10 sec. Basal levels of activity in the EAS were higher in the straining than in the extended position (P less than 0.005). The EAS responded to rapid rectal distension with inhibition of its activity. When changed to the straining position significant increases in muscular activity were observed after 35 cc of balloon insufflation (P less than 0.005). In the same muscle, slow distension produced an initial decrease in activity followed by significant increases after insufflation of 40 cc in the extended position and of 30 cc in the straining position. Basal activity in the LA was similar in both positions tested. The main effects of rectal distension in this muscle were increases in activity, significant only after high volumes of air inflation in the straining position (P less than 0.0001). Cutaneous stimulation disclosed a receptive field that was widespread for the EAS, extending over lumbosacral dermatomes (L3-S2), but greatly restricted for the LA. Responses to vaginal and cervical stimulation were more reliably obtained from the LA (P less than 0.001). These differences indicate that the EAS and LA muscles of the cat correspond with distinct, although related neural circuits.