Effects of beta-adrenoceptor antagonists on portal vein hypertension and ethanol-induced gastric mucosal damage in rats

Role of acute elevation of portal venous pressure by exogenous glucagon on gastric mucosal injury in rats with portal hypertension

Time-course studies revealed the increased susceptibility of the gastric mucosa to noxious injury in portal hypertension correlates with the level of elevated portal venous pressure and hyperglucagonemia. Whether acute elevation of portal venous pressure by exogenous glucagon aggravates such injury is not known. We tested the hypothesis that glucagon in a dose sufficient to acutely elevate portal venous pressure aggravates noxious injury of the gastric mucosa in rats with portal hypertension. Infusion of a portal hypotensive dose of somatostatin should reverse these changes. In anesthetized rats with portal vein ligation, glucagon, somatostatin or the combination was administered intravenously in a randomized, coded fashion. Acidified ethanol-induced gastric mucosal injury was determined. Portal venous pressure and gastric mucosal perfusion and oxygenation (reflectance spectrophotometry) were monitored to confirm the effects of the respective intravenous treatments. Exogenous glucagon exacerbated acidified ethanol-induced gastric mucosal injury. The exacerbation was attenuated by somatostatin. These changes paralleled the portal hypertensive and hypotensive effects of glucagon and somatostatin, respectively. Our data suggest that a unique mechanism is triggered with the onset of portal hypertension. In an antagonistic manner, glucagon and somatostatin modulate this novel mechanism that controls portal venous pressure and susceptibility of the gastric mucosa to noxious injury.

Portal hypertension and liver lesions in chronically alcohol drinking rats prevented and reversed by stable gastric pentadecapeptide BPC 157 (PL-10, PLD-116), and propranolol, but not ranitidine

Liver lesions and portal hypertension in rats, following chronic alcohol administration, are a particular target for therapy. Portal hypertension (mm Hg) assessed directly into the portal vein, and liver lesions induced by 7.28 g/kg b.w. of alcohol given in drinking water for 3 months, were counteracted by a stable gastric pentadecapeptide BPC 157, GEPPPGKPADDAGLV, M.W. 1419, known to have a beneficial effect in a variety of models of gastrointestinal or liver lesions (10 microg or 10 ng/kg b.w. i.p. or i.g.) and propranolol (10 mg/kg b.w. i.g.), but not ranitidine (10 mg/kg b.w. i.g.) or saline (5 ml/kg b.w. i.p./i.g.; control). The medication (once daily) was throughout either the whole 3 months period (1) or the last month only (2) (last application 24 h before sacrifice). In the background of 7.28 g/kg/daily alcohol regimen similar lesions values were assessed in control rats following alcohol consumption, after 2 or 3 months of drinking. Both prophylactic and therapeutic effects were shown. After a period of 2 or 3 months, in all control saline [intragastrically (i.g.) or intraperitoneally (i.p.)] treated rats, the applied alcohol regimen consistently induced a significant rise of portal blood pressure values over values noted in healthy rats. In rats that received gastric pentadecapeptide BPC 157 or propranolol the otherwise raised portal pressure was reduced to the values noted in healthy rats. Besides, a raised surface area (microm(2)) and increased circumference (microm) of hepatocyte or hepatocyte nucleus [HE staining, measured using PC-compatible program ISSA (VAMS, Zagreb, Croatia)] and an advanced steatosis [scored (0-4), Oil Red staining] (on 100 randomly assigned hepatocytes per each liver), an increased liver weight, all together parallel a raised portal pressure in controls. Some of them were completely eliminated (not different from healthy rats, i.e. portal pressure, the circumference and area of hepatocytes, liver weight), while others were markedly attenuated (values less than in drinking controls, still higher than in healthy rats, i.e. circumference and area of hepatocytes nucleus). On the other hand, ranitidine application attenuated only steatosis development. In summary, despite continuous chronic alcohol drinking, pentadecapeptide BPC 157, and propranolol may prevent portal hypertension as well as reverse already established portal hypertension along with related liver disturbances.

Potassium channels participate in gastric mucosal protection in rats with partial portal vein ligation

Glybenclamide, an adenosine triphosphate-dependent potassium (K+(ATP)) channel blocker, lowered portal pressure and attenuated the hyperdynamic splanchnic circulation in rats with partial portal vein ligation (PPVL). The purpose of this report was to confirm these observations and to test the hypothesis that glybenclamide could reduce acidified ethanol-induced gastric mucosal injury in rats with PPVL. Gastric mucosal blood flow (hydrogen gas clearance), systemic blood pressure, and portal pressure were monitored in rats with PPVL or sham operation (SO). Intravenous glybenclamide (20 mg/kg) or vehicle was administered, followed by intragastric acidified ethanol (0.15 N HCl and 15% ethanol). The area of gastric mucosal lesions was assessed by image analysis. In contrast to published findings, there was no significant elevation of portal pressure after glybenclamide administration in rats with PPVL. Glybenclamide did not alter the gastric mucosal hyperemia in these rats. Glybenclamide significantly increased mucosal injury. The data are consistent with the hypothesis that K+(ATP) channels play a role in protecting the gastric mucosa in rats with PPVL.

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.

A mechanistic study of beta-adrenoceptor antagonists on ethanol-induced gastric damage

The beta-adrenoceptor subtypes and the roles of myeloperoxidase and prostaglandin E2 in the anti-ulcer effect of beta-adrenoceptor antagonists were studied. A non-selective beta-adrenoceptor antagonist, propranolol, or selective beta-adrenoceptor antagonists, metoprolol (a beta 1-adrenoceptor antagonist) or butoxamine (a beta 2-adrenoceptor antagonist) were used. Propranolol given either intraperitoneally or orally reduced ethanol-induced mucosal damage and myeloperoxidase activity. Oral administration of butoxamine produced similar effects. The blood neutrophil count was increased after ethanol administration and this was reversed by the two drugs. Metoprolol did not affect myeloperoxidase activity, neutrophil count and mucosal damage under these experimental conditions. Oral administration of propranolol or butoxamine increased mucosal prostaglandin E2 level. It is concluded that the inflammatory responses to ethanol, as indicated by neutrophil infiltration in gastric mucosa, can be specifically inhibited by drugs that block beta 2-adrenoceptors. This action would explain in part why propranolol and butoxamine but not metoprolol lessened gastric damage. In addition, oral administration of propranolol and butoxamine increased the mucosal prostaglandin E2 level, which could partially contribute to their anti-ulcer effects.

A study of the antiulcer mechanisms of propranolol in rats

Although propranolol has been shown to protect against ethanol and stress ulceration, the antiulcer mechanisms are still unclear. The present study examined the antiulcer mechanisms of propranolol in three different types of ulceration induced respectively by ethanol (60%), indomethacin (30 mg/kg) and stress (cold-restraint). Propranolol pretreatment in the highest dose (10 mg/kg) given either intraperitoneally (i.p.) or orally (p.o.) prevented gastric mucosal damage in these three ulcer models. The three doses of the drug (2.5, 5 or 10 mg/kg) dose-dependently decreased systemic blood pressure which was accompanied by a reduction of gastric mucosal blood flow. These findings suggest that the protection was unrelated to an improvement of local circulation in the stomach. However, propranolol preserved the mucus levels in the three types of ulcer models. The beta-adrenoceptor blocker also increased the basal gastric mucosal potential difference. These findings indicate that propranolol strengthens the mucosal barrier by the preservation of mucosal mucus and enhancement of the mucosal integrity in the stomach.

The mechanistic pathway of gastric adaptive cytoprotection: a study on different components of the autonomic nervous system

1. The involvement of different components of the autonomic nervous system in the pathogenesis of ethanol-induced damage and the adaptive cytoprotection of mild irritants were studied in the gastric mucosa of male rats. 2. Capsaicin, yohimbine, and domperidone aggravated the 100% ethanol-induced gastric mucosal damage and attenuated the cytoprotective action of 20% ethanol, but not of 5% NaCl and 0.3 M HCl. Butoxamine and prazosin blocked the adverse actions of yohimbine and domperidone respectively. 3. Atropine, pirenzepine, and lidocaine lessened the severity of 100% ethanol-induced mucosal injury and further increased the cytoprotective action of 5% NaCl and 0.3 M HCl, but not of 20% ethanol. 4. Our results demonstrated that sensory afferent neurones, alpha 2-adrenoceptors and D2-dopaminergic receptors all play a significant role in the defensive mechanism of the gastric mucosa and the adaptive cytoprotection of 20% ethanol, while the M1- and M2-muscarinic receptors and sensory chemoreceptors on the gastric mucosa contribute only to the former action. The adverse effect of yohimbine and domperidone on lesion formation is probably mediated through the release of catecholamines, which subsequently act on the beta 2- and alpha 1-adrenoceptors respectively.