Characteristics of the internal anal sphincter and the rectum of the vervet monkey.

Abstract

SUMMARY1. The physiology of the internal anal sphincter of the vervet monkey was investigated.2. Strips of sphincter in vitro contracted to noradrenaline and adrenaline; adrenoceptors were mainly a-excitatory. Strips of rectal circular muscle relaxed to noradrenaline and contained both inhibitory a-and fi-adrenoceptors.3. All strips contracted to acetylcholine. After hyoscine or atropine, high doses of acetylcholine relaxed all strips by stimulating intramural inhibitory neurones as relaxations were blocked by tetrodotoxin and hexamethonium. Nicotine and DMPP gave relaxations with similar characteristics.4. It was concluded that relaxations to acetylcholine, nicotine and DMPP were not adrenergic as relaxations still occurred in strips from sympathetically denervated or reserpinized animals. The block of these relaxations by propranolol and guanethidine was considered to be unrelated to their actions as adrenergic blocking drugs.5. All strips relaxed to field electrical stimulation (1-5 Hz) through stimulation of intramural inhibitory neurones as tetrodotoxin blocked these relaxations. Adrenergic blocking drugs, prior reserpinization or prior section of the hypogastric nerves did not block these responses. The relaxations were not therefore adrenergic.6. 5-Hydroxytryptamine relaxed all strips but was not the transmitter in relaxations to acetylcholine, DMPP or nicotine, nor to field electrical stimulation, as desensitization of strips to 5-HT did not alter these responses.7. The circular smooth muscle of the internal anal sphincter had a dense terminal adrenergic innervation which rapidly decreased orad.8. In vivo, hypogastric nerve stimulation relaxed the rectum but contracted the sphincter. Sacral nerve root stimulation caused an after-contraction in both rectum and sphincter. In vivo, a close arterial injection of adrenaline or noradrenaline inhibited the spontaneous contraction waves of the rectum, but contracted the sphincter. Both these responses were blocked by phentolamine. 9. It was concluded that the internal anal sphincter is a discrete high pressure zone which has excitatory cholinergic and adrenergic innervations and an inhibitory non-adrenergic innervation.

Pelvic Nerve Stimulation Evokes Nitric Oxide Mediated Distal Rectal Relaxation in Pigs

“…Pelvic nerve stimulation (PNS) has shown different internal anal sphincter (IAS) responses in various species, 2,3,7,[9][10][11][12][13][14][15] but the majority of studies have found an inhibitory effect with reduced anal canal pressure. The rectal response to PNS has been found to be excitatory with increased pressure and reduced volume.…”

Animal Model for the Study of Internal Anal Sphincter Activity

“…In recent years some progress in the un derstanding o f the nervous control o f the IAS has been made by using animal models such as the vervet monkey [8] , Using the rat model we have dem onstrated [7] that in this animal the rectoanal reflex is also mediated by a noncholinergic, nonadrenergic transmitter. The inhibitory neurotransmitter may be used in medical treatment o f Hirschsprung's disease, in which the IAS fails to relax and the anal pres sure remains constantly high [6].…”

“…In vivo experiments have been done in cats [5] and monkeys [8]. This paper describes a simple and reliable model for studying IAS function in the rat.…”

Ano‐rectal activity in man during rectal infusion of saline: a dynamic assessment of the anal continence mechanism.

“…can be induced by balloon distension of the rectum without any evidence of rectal contraction. This is a local reflex mediated by non-adrenergic non-cholinergic inhibitory nerves (Rayner, 1979;Garrett, Howard & Jones, 1974). External sphincter contraction can also be elicited independently of rectal contraction by moderate distension of the rectum by a balloon, and Parks and his colleagues (Parks, Porter & Melzak, 1962) have shown that this is a spinal reflex.…”