text: On the possible role of different endogenous opiate receptors in gastroduodenal ulceration of the rat.
  In Wistar rats of both sexes stress(restraint)- and drug (indomethacin)-induced gastric, as well, as cysteamine-induced duodenal ulceration was treated by morphine and nalorphine, given either alone or in combination. Neither morphine nor nalorphine had a significant anti-ulcerogenic effect. In contrast, the combined morphine + nalorphine treatment showed a highly significant anti-ulcerogenic action in the case of gastric ulceration but it was ineffective on duodenal ulcer formation. It seems that the chi and sigma endogenous opiate receptors play a significant role in the anti-ulcerogenic effect, while the mu receptors are involved to a considerably lesser degree. Moreover, the experimental results strengthen the view that gastric and duodenal ulceration are two different pathological entities and that ulcer formation is only a common consequence.