Effect of diabetes on the morphine-induced inhibition of gastrointestinal transit

The effect of diabetes on the morphine-induced inhibition of gastrointestinal transit was examined in mice. Morphine dose-dependently inhibited gastrointestinal transit after s.c. administration in both non-diabetic mice and diabetic mice. There was no significant difference between the ED₅₀ values for this antitransit effect of morphine in non-diabetic and diabetic mice. The gastrointestinal antitransit effect of morphine was significantly antagonized by pretreatment with β-funaltrexamine (40 mg/kg, s.c.), a selective μ-opioid receptor antagonist, in both non-diabetic and diabetic mice. However, pretreatment with naloxonazine (35 mg/kg, s.c.), a selective μ₁-opioid receptor antagonist, had no effect on the antitransit properties of morphine. These results suggest that diabetes failed to alter the μ₂-opioid receptor-mediated antitransit effect of morphine.