Somatic nerve stimulation and cholera-induced net fluid secretion in the small intestine of the rat: Evidence for an opioid effect

Abstract

The effects of somatic nerve stimulation on cholera toxin induced secretion was investigated in vivo in anaesthetised rats. Small intestinal secretion was induced with cholera toxin and measured by a gravimetric technique. Afferent stimulation (pulse frequency within train; 100 Hz; train duration: 50 ms; train frequency: 3 Hz) of the sciatic nerve over 30 min significantly reduced the net fluid secretion both during ( P<0.05) and after cessation of the stimulation ( P<0.01). The greatest effect was obtained immediately after the termination of the nerve stimulation when the secretion was reversed to net fluid absorption. The opioid receptor antagonist naloxone (10 mg kg −1 i.v.) administrated during the stimulation, significantly inhibited the antisecretory effect seen after the stimulation, thus no significant difference was seen between the control period and the periods after cessation of the stimulation. The opioid receptor antagonist naloxone methiodide (10 mg kg −1 i.v.), which does not cross the blood–brain barrier, partly inhibited the antisecretory effects but not with the same magnitude as naloxone, thus the net fluid secretion was still significantly inhibited after the stimulation ( P<0.05). We conclude that afferent stimulation of the sciatic nerve strongly inhibits the cholera toxin induced secretion in the small intestine. This inhibition involves primarily a central opioid mechanism and to a lesser extent peripheral opioid mechanism.