Effect of acute and chronic administration of L-arginine on morphine induced inhibition of gastrointestinal motility.

Effect of acute and chronic administration of L-arginine on morphine induced gastrointestinal inhibition was tested in rats. In the test for acute effect, L-arginine (200 mg/kg, i.v.) was given 10 minutes before the charcoal meal test. In the test for chronic effects, L-arginine (200 mg/kg, i.v.) was given twice a day for 4 days. Charcoal meal test was done on the fifth day. Morphine was administered 45 minutes before the charcoal meal test. Results showed that acute administration of L-arginine did not affect the morphine's action on the GIT. In contrast, chronic administration of L-arginine reversed the morphine induced decrease in gastrointestinal motility. The reversal was however, not complete. This data suggests that inhibition of NO may be one of the mechanism of morphine induced constipation.