Reflex adrenergic inhibition of colonic motility in anesthetized rat caused by nociceptive stimuli of peritoneum

Abstract

Nociceptive stimulation of the peritoneum inhibits colonic motility via a sympathoadrenergic reflex. This sympathetic reflex most probably induces the inhibition indirectly via a presynaptic blockade of cholinergic transmission. To further clarify this reflex, colonic motility was continuously recorded by a volume method in rats exposed to nociceptive abdominal stimulation and intravenous drug administration. Intraabdominally applied HCl inhibited colonic motility, which was unaffected by nonselective β-adrenoceptor blockade (propranolol). However, the nonselective α-adrenoceptor antagonist phentolamine and the selectiveα ₂-adrenoreceptor antagonist yohimbine restored motility. Spontaneous colonic motility was unaffected by the nonselective β-adrenoceptor agonist (isoproterenol) and the selectiveα ₂-adrenoreceptor agonist (l-phenylephrine). On the other hand, a nonselective α-agonist (noradrenaline) and a selectiveα ₂-adrenoreceptor agonist (clonidine) inhibited spontaneous colonic motility. It is suggested that in the rat sympathetic reflex inhibition of colonic motility caused by abdominal nociception is mediated via presynapticα ₂-adrenoreceptor inhibiting the excitatory cholinergic nuerons.