Morphine modulates microvascular leakage dose-dependently in the airway of ovalbumin-sensitized rats

Results: Morphine (1-10 mg/kg) inhibited ovalbumin-evoked increase in microvascular plasma leakage in a dosedependent manner; however, it had no significant effect at the doses of 0.1 or 30 mg/kg. In addition, morphine, at the doses of 1-30 mg/kg, abolished microvascular leakage increased by capsaicin. The inhibition caused by morphine was blocked by the peripheral opioid receptor antagonist, naloxone methiodide, in ovalbumin or capsaicin series. Morphine or naloxone methiodide has alone no effect on plasma leakage.