Dual effects of zinc sulphate on ethanol-induced gastric injury in rats: possibly mediated by an action on mucosal blood flow

The present study examines the protective effect of zinc sulphate against ethanol-induced gastric mucosal ulcers in rats. Absolute ethanol decreased the gastric mucosal blood flow and produced haemorrhagic lesions in the glandular mucosa. Zinc sulphate preincubation in an ex-vivo stomach chamber preparation prevented the formation of ethanol-induced lesions and attenuated the decrease of blood flow produced by ethanol. Subcutaneous injection of the same doses of the drug at 15 and 30 min before ethanol exposure, markedly reduced the blood flow and also aggravated ethanol-induced gastric injury; however, when injected at 23 and 24 h before ethanol administration, zinc sulphate protected against lesion formation but had no effect on the vascular changes induced by ethanol in the gastric glandular mucosa. These findings show that the antiulcer effect of zinc sulphate occurs only when the drug is given orally, or injected s.c. 23 and 24 h before ethanol challenge. Furthermore, this protective action is probably not entirely mediated by preservation of the gastric mucosal blood flow.

The antiulcer effect of verapamil in relation to gastric calcium levels in stressed rats

The antiulcer effect of verapamil, and its relationship to stomach calcium levels, were examined in rats restrained at 4 degrees C (stress). Stress for 2 hr significantly increased muscle calcium and induced mucosal ulceration in the gastric glandular segment; calcium concentrations in the glandular mucosa and serum were unaffected. Verapamil or calcium gluconate given 30 min before stress prevented the rise in gastric muscle calcium, and attenuated ulcer severity. Bis(beta-aminoethylether)-NNN'N'-tetra-acetic acid (EGTA) pretreatment, however, further elevated stomach muscle calcium and markedly worsened lesion formation. These findings suggest that increased stomach muscle calcium could be a causal factor in stress-induced gastric glandular ulceration.

The protective mechanisms of paracetamol against ethanol-induced gastric mucosal damage in rats

The protective mechanisms of paracetamol against ethanol-induced gastric mucosal damage have been examined. The antiulcer action of subcutaneously (s.c.)-injected paracetamol, 250 mg kg-1, was attenuated by either subdiaphragmatic vagotomy or s.c. injection of N-ethylmaleimide, 10 mg kg-1. This attenuation was not seen in rats given paracetamol by the oral route (p.o.). Indomethacin pretreatment, 5 mg kg-1, did not influence the lesion-preventing action of paracetamol given s.c. or p.o. The findings suggest that the antiulcer effect of s.c.-administered paracetamol results from an action involving the vagal nerve and tissue sulfhydryls, but not prostaglandins. On the other hand, the protective mechanism of paracetamol p.o. is independent of the vagal system or tissue sulfhydryls and prostaglandins. It seems that paracetamol given p.o. exerts its antiulcer effect by acting directly on the mucosal cell to strengthen mucosal integrity.

Does acidosis contribute to stress-induced ulceration in rat stomachs?

The present study examines the involvement of acidosis in stress ulceration in rat stomachs. Cold restraint stress for 2 hr did not affect the blood lactate level; however, it produced respiratory acidosis, as reflected by the depressed respiratory rate which was associated with increased CO2 tension and a lowered blood pH. Severe hemorrhagic ulceration was found in the glandular mucosa. The effects of stress on blood pH and the stomach were reversed by IV infusion of NaHCO3. Infusion of HCl IV decreased the blood pH and HCO-3 level and produced gastric ulceration. It is concluded that respiratory acidosis could be involved in stress ulceration. The metabolic acidosis evoked by HCl also induced gastric damage, but the effect was much less.

Arterial catecholamine levels in morphine-treated rats subjected to sympathetic nerve stimulation

1. The effect of acute or chronic morphine treatment on the changes in arterial noradrenaline and adrenaline levels in response to sympathetic nerve stimulation was studied in rats. 2. Rats which had been chronically treated with morphine in their drinking fluid for 21 days were shown to be morphine-tolerant, as revealed by the tail-immersion test for analgesia. 3. It was found that animals given either acute or chronic morphine treatment had similar basal concentrations of arterial catecholamines to their controls. 4. Sympathetic nerve stimulation produced significant increases in arterial noradrenaline and adrenaline levels in both the control and morphine-treated animals. However, the degree of arterial noradrenaline elevation was significantly less in morphine-tolerant animals. 5. This phenomenon was not observed in acutely morphine-treated rats or at 2 weeks following opiate withdrawal in animals which had been treated previously with morphine for 3 weeks. 6. The findings suggest that chronic morphine treatment in rats not only leads to opiate tolerance but also reduces catecholamine release in response to sympathetic nerve stimulation.

The protective mechanism of FPL55712 against stress-induced gastric ulceration in rats

Cold-restraint stress produced stomach ulceration which was accompanied by a decreased glandular mucosal mast cell count and blood flow. Pretreatment with FPL55712, a leukotriene antagonist, dose-dependently prevented ulcer formation and mast cell depletion; however, it did not affect the reduced mucosal blood flow, nor did it significantly influence acid secretion and pepsin output. The role of the leukotrienes in stress ulceration is discussed in the light of the findings with FPL55712 on gastric glandular mucosal mast cell degranulation.

The identification of pyrrolizidine alkaloid-containing plants--a study on 20 herbs of the Compositae family

Twenty Chinese medicinal herbs of the Compositae family were investigated for the presence of pyrrolizidine alkaloid. Of these, only the Eupatorium species were shown to contain pyrrolizidine alkaloid. The amount present was found to vary with species, parts of the plant used, purchase sources and extraction methods. Possible toxicity from the use of these herbs is discussed.

A comparative study on the hepatic toxicity and metabolism of Crotalaria assamica and Eupatorium species

The oral LD50 of Crotalaria assamica, which contains mainly monocrotaline, was found to be 154 mg/kg in mice. Neither liver necrosis nor morbidity was demonstrated with Eupatorium extract at a dose level of 144 mg/kg, which was equivalent to the LD20 of Crotalaria. Pretreatment with phenobarbitone enhanced the toxicity of both plant extracts in mice. In in vitro studies, "metabolic pyrrole" was formed by incubating Eupatorium japonicum extracts with liver microsomes. The rate of "pyrrole" formation was similar to that of Crotalaria extract and pure monocrotaline alkaloid, but was much slower than retrorsine. The rate of N-oxide formation was, in descending order, retrorsine, Eupatorium japonicum and Crotalaria/monocrotaline. It is concluded that the alkaloid in Eupatorium species is metabolized to "pyrrole" and an N-oxide metabolite in the liver, but hepatotoxicity is much lower when compared with that caused by Crotalaria.

Effects of zinc and cholesterol/choleate on serum lipoproteins and the liver in rats

The effects of short-term treatment with orally-administered zinc sulphate and/or a mixture of cholesterol/choleate on serum lipoprotein and hepatic enzyme levels were studied. Administration of graded doses of zinc sulphate (20 or 40 mg/kg, as zinc ion) for 5 days, dose-dependently increased serum and hepatic zinc levels but depressed the serum high-density lipoprotein-cholesterol (HDL-C) concentration and liver cytochrome P-450 activity. However, it did not affect hepatic concentrations of malondialdehyde and free beta-glucuronidase. Cholesterol/choleate treatment for 5 days markedly damaged the liver, as reflected by elevations of hepatic concentrations of malondialdehyde (both in the mitochondrial and microsomal fractions) and of free beta-glucuronidase; total cholesterol and low-density lipoprotein-cholesterol in the blood were increased, whereas HDL-C was decreased significantly. Concomitant administration of zinc sulphate with cholesterol/choleate further lowered HDL-C levels, but reversed the high hepatic concentrations of both malondialdehyde and free beta-glucuronidase. The present study indicates that both zinc ions and cholesterol can decrease circulatory HDL-C levels and that zinc protects against cholesterol-induced hepatic damage by reducing lysosomal enzyme release and preventing lipid peroxidation in the liver.

The possible role of metabolic acidosis in acetazolamide-induced gastric lesion formation in rats

The effects of acetazolamide on blood acid/base balance and the relationship of the latter to gastric lesion formation were studied in rats. Acetazolamide (200 mg/kg, s.c.) produced haemorrhagic gastric lesions which were accompanied by lowered arterial blood pH and HCO3- levels. High dose (6.2%) of NaHCO3 infusion normalised the arterial blood pH and decreased lesion formation. It also markedly raised the blood HCO3- level. However, a lower dose (3.1%) of the drug only raised the HCO3- to a normal level and slightly reduced the severity of ulceration. These results suggest that metabolic acidosis is the main causative factor while depletion of blood HCO3- may play a minor role in acetazolamide-evoked lesion formation in rat stomachs.

Changes in arachidonic acid metabolite patterns in alloxan-induced diabetic rats

The vasodepressor responses to intravenous injections of arachidonic acid, and the formation of its metabolites, were studied in rats made diabetic 1 or 2 weeks after a 1-dose alloxan treatment. Arachidonic acid dose-dependently decreased the diastolic blood pressure in normal animals, but this hypotensive effect was significantly weaker in 2-week postalloxan-treated rats. Indometacin abolished arachidonic-acid-induced depressor responses in both normal and diabetic animals. Hypotension induced by sodium nitroprusside was of the same magnitude in non-diabetic and insulin deficient rats. Plasma levels of thromboxane B2 were significantly increased in both the 1- and 2-week diabetic rats, being greater in the latter group; those of 6-keto-PGF1 alpha remained unchanged during the 2-week diabetic period. It is concluded that the attenuation by diabetes of depressor responses to arachidonic acid could be due to changes in the thromboxane/prostacyclin balance, with thromboxane formation being elevated whereas prostacyclin generation remains unaffected.

Paracetamol confers resistance to ethanol-induced gastric mucosal damage in rats

Paracetamol given orally or subcutaneously did not produce any observable gastric mucosal damage, nor did it change the acidity of the residual secretion in rat stomachs. However, it delayed the gastric emptying rate and increased the residual volume of gastric secretion. Pretreatment with paracetamol 250 mg kg-1 significantly prevented ethanol-induced gastric ulceration. Although it did not influence ethanol-stimulated acid secretion, it increased the mucosal mucus content in the ethanol-treated animals. The findings suggest that the protective mechanism of paracetamol against ethanol-induced damage is likely to be due to improved gastric mucosal integrity, through an increase in the adherent mucosal mucus which protects the underlying delicate cellular structures.

The influence of omeprazole on the protective effects of secretagogues against ethanol-induced gastric ulceration in rats

The influence of omeprazole on the antiulcer effects of histamine, methacholine and pentagastrin on ethanol-induced gastric ulceration was studied. Histamine 5 mg/kg, methacholine 500 micrograms/kg or pentagastrin 100 micrograms/kg pretreatment s.c. markedly reduced ethanol (50%, 10 ml/kg p.o.)-induced gastric ulceration in pylorus-ligated conscious rats, but significantly elevated the gastric secretory volume and acid output. Omeprazole pretreatment 50 mg/kg s.c. reduced gastric secretion and abolished the ulcer-protecting effects of the three secretagogues. The same doses of histamine, methacholine or pentagastrin did not significantly alter the gastric secretory volume but increased the total acid output of ex-vivo stomach chamber preparations in anaesthetised animals. Histamine worsened ethanol-evoked ulceration whereas methacholine and pentagastrin had no effect on the lesions. Omeprazole pretreatment did not prevent ulcer aggravation by histamine. It is concluded that the antiulcer effects of the three secretagogues in conscious animals are probably due to the increased secretory volume which lessens the ulcerogenic action of ethanol by its dilution. Omeprazole reduces the secretory volume and thus prevents the antiulcer effect of these secretagogues. The findings with histamine and omeprazole in the ex-vivo stomach experiments support the suggestion that it is unlikely that increased gastric acid secretion affects the ulcerogenicity of ethanol in rat stomach.

The protective effects of sulphasalazine against ethanol-induced gastric damage in rats

1 The inhibitory action of sulphasalazine on ethanol-induced gastric damage was studied in rats. 2 Sulphasalazine (62.5 or 125 mg kg-1, s.c.) did not affect basal gastric acid secretion but increased pepsin output. 3 Ethanol (40% v/v, 10 ml kg-1, p.o.) produced severe gastric glandular mucosal damage and lessened the stomach emptying rate of resin pellets, but it increased the levels of prostaglandin E2 (PGE2)-like activity in the glandular mucosa. 4 Sulphasalazine markedly prevented ethanol-induced damage and significantly elevated gastric wall mucus levels both in basal conditions and in the presence of ethanol. 5 Sulphasalazine caused a small insignificant increase in mucosal PGE2 levels in both control and ethanol-treated rats. The drug significantly increased mucosal PGE2 levels in indomethacin-treated animals, but did not prevent indomethacin-induced mucosal damage. 6 Sulphapyridine but not 5-aminosalicylic acid, constituents of sulphasalazine, showed a similar antilesion action to the parent drug, and prevented gastric wall mucus depletion in ethanol-treated animals. 7 This study elucidates the protective effects of sulphasalazine against ethanol-induced gastric lesions. The antagonistic action appears to be mediated, at least partly, through the preservation of gastric wall mucus by sulphapyridine.

Morphine reduces vagal-stimulated gastric acid secretion through a central action

The influence of morphine on gastric acid secretion stimulated by 2-deoxy-D-glucose or electrical vagal stimulation was studied in anaesthetised rats with perfused stomachs. It was found that changes in gastric acid output induced by electrical vagal stimulation were not noticeably affected, whereas those evoked by 2-deoxy-D-glucose were significantly suppressed by morphine pretreatment. The depressant effect of the opiate on the acid secretion stimulated by 2-deoxy-D-glucose was abolished by naloxone pretreatment. It is suggested that morphine inhibits vagal-stimulated gastric acid secretion in rats by acting predominantly on opioid receptors in the central nervous system.

Zinc deficiency: its role in gastric secretion and stress-induced gastric ulceration in rats

The effects of zinc deficiency on gastric secretion and on cold-restraint stress-induced ulceration in rat stomachs have been studied. Administration of graded zinc deficient diets for 5 weeks significantly depressed the serum zinc concentration and decreased body weight gain in the rats. These diets significantly increased the gastric secretory volume, acid and pepsin. Zinc deficiency produced or aggravated the formation of glandular ulceration in the absence or presence of stress, respectively; it also decreased the mast cell count in the gastric glandular mucosa. It is concluded that zinc deficiency adversely affects the rats by reducing the body weight gain and producing ulceration which is probably mast cell-mediated. On the other hand, it increases gastric secretory functions.

Effects of Sophora flavescens Ait. on haemodynamics and ventricular fibrillation threshold in anaesthetized dogs

The effects of an ethanol extract of the plant Sophora flavescens Ait. on haemodynamics and ventricular fibrillation threshold were studied in pentobarbitone-anaesthetized dogs. It was found that intravenous injection of the extract, 120 mg/kg, caused transient but significant depression in systolic and diastolic blood pressure, heart rate, left ventricular pressure and dLVP/dtmax, as well as elevation of ventricular fibrillation threshold. These preliminary findings suggest that the ethanol extract of Sophora flavescens Ait. possesses pharmacological activities resembling those of antiarrhythmic agents, but the mechanisms of action are unclear.

Effects of ethanol and nicotine on gastrin and somatostatin release in rats

An intravenous bolus injection of nicotine (1 mg/kg) markedly elevated gastric acid secretion; oral administration of ethanol (40%, 10 ml/kg) significantly increased arterial serum gastrin and somatostatin levels. Chronic pretreatment with oral nicotine (5 or 25 micrograms/ml in drinking tap water, for 10 days), but not acute pretreatment with a single oral dose of nicotine (2 or 4 mg/kg), inhibited the nicotine-induced gastric acid secretion and ethanol-induced gastrin and somatostatin release. Pretreatment subcutaneously with a ganglion-blocking dose of hexamethonium (10 mg/kg), however, inhibited nicotine-stimulated acid output and ethanol-evoked somatostatin secretion but not ethanol-induced gastrin release. It is concluded that ethanol-evoked gastrin secretion could be due to activation of specific sites which are not nicotinic receptors, but which are depressed by chronic nicotine pretreatment. On the other hand, the release of somatostatin by ethanol appears to be controlled by ganglionic receptors in the gut.

A comparative study on the pyrrolizidine alkaloid content and the pattern of hepatic pyrrolic metabolite accumulation in mice given extracts of Eupatorium plant species, Crotalaria assamica and an Indian herbal mixture

Plants belonging to the Eupatorium species, E. japonicum Thunb, E. fortunei and E. chinense, were found to contain very low concentrations of pyrrolizidine alkaloid compared with a known hepatotoxic Indian herbal mixture and Crotalaria assamica. High concentrations of pyrrolic metabolite were detected in livers of mice given a single oral dose of extracts of Indian herbal mixture or C. assamica but not in the case of the Eupatorium species. Also, accumulation of pyrrole metabolites was not demonstrated with chronic administration of decoctions prepared from herbs of the Eupatorium species.

Effects of hypoxaemia and hyperoxaemia on some cardiovascular responses of rats to adrenaline

Systemic blood pressure and pulse rate responses to intravenously administered adrenaline during hypoxaemia or hyperoxaemia were studied in urethane-anaesthetized rats. Hypoxaemia or hyperoxaemia was induced by ventilating the animals with 15% O2/85% N2 or with 100% O2, respectively. Hypoxaemia significantly decreased the diastolic blood pressure and elevated the pulse rate; the reflex falls in pulse rate in response to adrenaline were significantly reduced. Hyperoxaemia, on the other hand, did not cause remarkable changes in blood pressure or pulse rate, but significantly depressed diastolic blood pressure to adrenaline. It is suggested that the compensatory cardiovascular reflexes may be impaired by hypoxaemia, and that hyperoxaemia reduces vasoconstrictor response to catecholamine possibly by lessening or enhancing the sensitivities of the vascular alpha 1- or beta 2-adrenoceptors, respectively.

Captopril does not potentiate hypotension and algesia by substance P

Captopril (1-5 mg/kg, i.v.) did not affect the vasodepressor responses to substance P (1-30 micrograms/kg, i.v.) in anaesthetized rats. Substance P (100 micrograms/kg, s.c.) produced significant algesia in mice; this was not potentiated by the smaller doses of captopril (1-2 mg/kg, i.p.), but was instead antagonized by the high dose (5 mg/kg, i.p.). It is concluded that captopril does not have any influence on substance P degradation in vivo since the pharmacological actions of the undecapeptide are not enhanced after captopril treatment.

Production of physical dependence in rats by drinking a morphine solution

The plasma concentrations of morphine and glucose, the body weight, and the severity of the naloxone-precipitated withdrawal syndrome were studied in female rats in which morphine dependence was induced by administration of the opiate, with or without sucrose, in their drinking water. It was found that sucrose encouraged the animals to consume more morphine and that the initial plasma concentrations of the opiate, as well as the rate of development of physical dependence, were higher than the group not given sucrose. Plasma glucose concentrations, maximum plasma morphine levels and the maximum severity of the naloxone-precipitated withdrawal syndrome were, however, not significantly different between the two groups. The findings suggest that both regimens of administering the opiate in drinking fluid are effective in inducing morphine dependence in rats; the addition of sucrose tends to speed up the development of physical dependence, probably by increasing intake of the opiate through consuming more sucrose solution.

Luminal acid in stress ulceration and the antiulcer action of verapamil in rat stomachs

The role of luminal acid and the influence of the antisecretory action of verapamil in stress ulcer prevention in rat stomachs have been studied. Intraperitoneally injected verapamil, 4 mg kg-1, inhibited gastric acid secretion and ulcer formation, however, a 2 mg kg-1 dose, which did not significantly influence acid output, also had an antiulcer effect. Intraperitoneal injection of bethanechol, 1.2 or 3.6 mg kg-1, increased gastric acid output, but did not influence stress-induced ulcer formation. Oral administration of HCl, 25 or 50 mu equiv, aggravated stress ulceration in a dose-dependent manner; this lesion-worsening effect was prevented by pretreatment with verapamil or bethanechol. The gastric luminal acid content in 2 h pylorus-ligated rats was similar in the groups given either bethanechol or HCl. These findings indicate that the antisecretory action of verapamil may not account for its antiulcer effect. It is suggested that endogenous and exogenous luminal acid may have different influences on stress ulcer formation.

Effects of cold-restraint stress on gastric ulceration and motility in rats

The effects of stress by restraint at 4 degrees C for 2 hr and of drug treatment on gastric lesion formation and motor activities (contraction frequency, amplitude and tone) were studied in rats. Restraint at room temperature (22 degrees C) produced a small ulcer index in the controls and did not significantly affect gastric motor activities; atropine and verapamil reduced but bethanechol increased gastric contractions under the same experimental conditions. Restraint at 4 degrees C markedly elevated the ulcer index. The frequency of gastric contractions was significantly increased in the first hr but the amplitude was depressed during the whole 2-hr observation period. Gastric tone initially fell but rose in the second hr of cold-restraint stress. Atropine and verapamil pretreatment prevented stress-induced ulcer formation and suppressed the frequency and amplitude of gastric contraction. Bethanechol stimulated both frequency and amplitude without significantly influencing stress ulcer size. It is unlikely that gastric hypermotility plays a major role in stress ulceration; the stomach smooth muscle-relaxing action of atropine and verapamil may contribute only partly to their antiulcer effects.

Effects of eight-week treatment with histamine H2-antagonists or an antacid on plasma levels of histamine and serotonin in duodenal ulcer patients

The effects of 8-week treatment with oral histamine H2-antagonists (ranitidine or cimetidine) or an antacid on plasma levels of histamine and serotonin were studied in duodenal ulcer patients. Histamine H2-antagonists significantly elevated plasma histamine levels, however, they markedly decreased serotonin concentrations by the 4th week of treatment. Antacid treatment similarly increased histamine levels without significantly affecting blood serotonin. It is concluded that changes in intragastric or intraduodenal acidity affect histamine release, as reflected by increased blood levels; serotonin secretion could be influenced by blocking histamine H2-receptors, possibly those located mainly in the gastrointestinal tract.