The inhibitory action of ethanol on the gastric mucosa and its interaction with the vagus in rats

Effects of selective beta-adrenoceptor antagonists on gastric ulceration in the rat

Metoprolol and butoxamine, beta-adrenoceptor antagonists which act selectively at the beta 1- and beta 2-adrenoceptors, respectively, have been investigated for their actions on the ethanol, indomethacin and cold-restraint stress ulcer models. Oral administration of butoxamine but not metoprolol significantly attenuated gastric mucosal damage in the three types of ulcer model. Intraperitoneal injection of butoxamine reduced indomethacin ulceration but not that of the other two models. The stimulatory effect of butoxamine on the gastric mucosal potential difference and intramucosal mucus level correlated positively with its anti-ulcer action. Only oral administration of butoxamine significantly increased the mucosal prostaglandin E2 (PGE2) level but not after intraperitoneal injection. Oral administration of butoxamine also significantly increased the mucosal PGE2 level in the three types of ulcer model but this drug was only effective in the indomethacin ulcer model after intraperitoneal injection. Gastric acid and pepsin output were not affected by either drug. Metoprolol significantly reduced systemic blood pressure; this could be attributed to a reduction in gastric mucosal blood flow. These results imply that beta 2-adrenoceptors play a significant role in the pathogenesis of gastric ulceration. We suggest that the anti-ulcer effect of butoxamine was in part a result of strengthening of the mucosal barrier but that this was not effected by modification of acid or pepsin secretions in the stomach. Stimulation of PGE2 in the gastric mucosa could contribute in part to the anti-ulcer action of the drug, especially when given by the oral route.

Role of dorsal motor nucleus of vagus in gastric function and mucosal damage induced by ethanol in rats

Experimental evidence indicates that the autonomic nervous system, especially the cholinergic pathway modulates the mucosal defensive mechanism and affects mucosal damage in the stomach. The present study investigated the role of the dorsal motor nucleus of vagus (DMV) in gastric function and its influences on ethanol-induced mucosal damage in pentobarbitone-anesthetized rats. Electrolytic lesion of the DMV as compared with sham operation and lesions of other brain areas, eg, nucleus reticular gigantocellularis and cuneate nucleus, reduced the basal gastric mucosal blood flow (GMBF) and also the blood flow after ethanol administration. The same operation did not affect the acid secretion either in the basal state or during the ethanol treatment period. Lesions at the caudal half of the DMV produced a bigger depression of GMBF when compared with lesion at the rostral half. In the sham-operated rats, ethanol induced severe hemorrhagic lesions in the gastric glandular mucosa, and this was significantly potentiated by lesions at the DMV, especially in the caudal half. The present findings indicate that acute DMV damage at the caudal half markedly affects the GMBF but not the acid secretion. The action on GMBF may contribute to the aggravation of ethanol-induced gastric damage in rats. These data reinforce the idea that the central vagal pathway, especially the caudal half of the DMV, plays a significant role in the modulation of GMBF, which in turn affects the integrity of gastric mucosal barrier.

Portal hypertension. Its effects on gastric function and ethanol-induced gastric mucosal damage in rats

The time-course effects of portal hypertension on gastric secretory function, mucosal blood flow, vascular permeability, and ethanol-induced gastric mucosal damage were examined in anesthetized rats. Partial ligation of the portal vein effectively produced portal hypertension one to three days later but the raised pressure returned to normal on the sixth day after ligation. This time-course effect coincided with reduced pepsin secretion and mucosal blood flow and also with potentiated ethanol-induced mucosal damage during the first to third days. These effects started to tail off on the sixth day. However, gastric acid output was significantly reduced on the third day, and this was strongest on the sixth day after operation. Portal vein ligation also reduced basal vascular permeability, which was markedly potentiated after ethanol treatment. It is concluded that: (1) portal vein blood pressure changes are a time-dependent process following ligation; (2) changes in gastric mucosal blood flow (GMBF) and lesion formation are closely related to portal hypertension; (3) gastric mucosal injury is associated with vascular damage, as evidenced by increased in vascular permeability; and (4) pepsin but not acid secretion is closely related to the state of the GMBF.

In vitro study of ethanol on the electrical parameters in rat stomachs

The electrophysiological effects of mucosal or submucosal ethanol (5, 10, or 20%) were assessed in isolated stomach preparation. Mucosal incubation with these concentrations of ethanol dose- and time-dependently decreased the transmucosal potential difference (PD), while the electrical current (I) and resistance (R) were unaffected. Submucosal exposure to the same concentrations of ethanol also reduced the PD, but to a lesser extent; only 20% of ethanol produced a significant effect. This same dose of ethanol not only decreased I but also increased R to a significant level. These findings indicate that transmucosal PD appears to be generated largely by the mucosal epithelial cell barrier, while the I and R are elicited by the laminea propria mucosa which is easily approached and altered by ethanol which acts from the submucosal side. The significance of the effects produced by mucosal or submucosal ethanol is discussed.