The effects of captopril and naloxone on restraint-cold-stress- and ethanol-induced gastric lesions in rats.

1. This study was undertaken to investigate the effect of captopril (1 microgram/kg or 1 mg/kg, i.p.) on the actions of naloxone (5 mg/kg, i.p. in gastric ulceration induced by ethanol and restraint-cold-stress. 2. Neither naloxone (5 mg/kg, i.p.) nor captopril (1 mg/kg, i.p.) alone induced any change in the indices of the ulcer in either group. 3. Captopril at a lower dose (1 microgram/kg, i.p.), when combined with naloxone (5 mg/kg, i.p.), significantly reduced cumulative ulcer length only in the ethanol-treated group (from 54.9 +/- 7.2 mm to 22.5 +/- 6.2 mm). 4. However, a high dose of captopril (1 mg/kg) plus naloxone pretreatment caused a significant reduction in both ethanol (from 54.9 +/- 7.2 mm to 24.9 +/- 6.5 mm) and restraint-cold-stress (from 19.0 +/- 3.0 mm to 5.3 +/- 1.0 mm)-induced ulcer formation. 5. Acetylsalycilic acid, when used together with captopril, increased the ulcer formation induced by stress. 6. Naloxone, by increasing the release of prostaglandins, has been shown to prevent ulcer formation induced by several noxious stimuli. 7. Therefore, the effect of the combination might be due to the synergistic interaction of both drugs on prostaglandin synthesis.