Experimental Studies on the Mechanism of the Recto-anal Reflex

Abstract

The mechanism of the recto-anal reflex (R.A.R), i.e, transient fall of anal canal pressure induced by rectal distension, is still obscure. In order to elucidate the role of the sacral nerves to R.A.R., the effects of denervation and stimulation of the sacral nerves were examined experimentally in dogs. A laminectomy was done to expose the sacral nerve roots in each dog. Each and/or all sacral nerves were tied and devided or stimulated extradurally. In chronic experiments, R.A.R was examined repeatedely over two weeks after operation. R.A.R was not obtained when all sacral nerves were devided, but when any indivisual sacral nerve was remained undivided, R.A.R was elicited in all dogs. In acute experiments, electrical stimulation of the sacral nerve (especially S_1 and S_2) brought about a transient fall of the anal canal pressure and a marked inhibition of sustained electrical activity of the internal anal sphincter muscle. Both were identically seen in pressure and muscle while the rectum was distended by a balloon. The results indicate that the recto-anal reflex is dependent not only on the intramural pathway but also on the sacral nerve pathway when this reflex action is elicited in a physiological condition.