Effects of octreotide on responses to colorectal distension in the rat

Background and aims-It has been suggested that the analgesic effect of the somatostatin analogue octreotide in visceral pain involves peripheral mecha nisms. We evaluated the effect of octreotide on responses to noxious colore ctal distension in rats. Methods-In a behavioural study, presser and electromyographic responses to colorectal distension were evaluated before and after intravenous or intrat hecal administration of octreotide. In pelvic nerve afferent fibre recordin gs, responses of mechanosensitive fibres innervating the colon to noxious c olorectal distension (80 mm Hg, 30 seconds) were tested before and after oc treotide. Results-Octreotide was ineffective in attenuating responses to colorectal d istension in either normal or acetic acid inflamed colon when administered intravenously but attenuated responses when given intrathecally. Administra tion of octreotide over a broad dose range (0.5 mug/kg to 2.4 mg/kg) did no t alter responses of afferent fibres to noxious colorectal distension in un treated, or acetic acid or zymosan treated colons. Conclusions-In the rat, octreotide has no peripheral (pelvic nerve) modulat ory action in visceral nociception. The antinociceptive effect of octreotid e in this model of visceral nociception is mediated by an action at central sites.