The influence of morphine on acid secretion by the isolated rat gastric mucosa

The influence of morphine on acid secretion by the isolated gastric mucosa was studied in adult rats. A wide range of morphine concentrations (1 X 10(-4) to 1.6 X 10(-3) M) was found to have no effect on basal acid output, or on acid secretion maximally stimulated by bethanechol or histamine. It is suggested that the opiate receptors in the rat gastric mucosa, if there are any, are not involved in modulating acid secretion.

Gastric secretion and mucosal lesions in morphine-dependent rats

The gastric mucosa and basal gastric secretion of morphine-dependent rats with pyloric occlusion were examined. Morphine tolerance and dependence were induced by administering increasing concentrations of morphine sulphate in the drinking water for 3 weeks, and were confirmed by a decreased analgesic response to morphine in the tail-immersion test and by occurrence of a naloxone-precipitated withdrawal syndrome, respectively. It was found that although the basal gastric secretion of morphine-dependent rats was not significantly different from that of naive animals, the former group showed a significantly higher gastric glandular mucosal ulcer index. Intraperitoneal injection of naloxone induced significant withdrawal effects but did not produce significant changes in gastric secretion or in ulcer index.

Effects of hypoventilation on the cardiovascular responses of rats to adrenaline and acetylcholine

Blood pressure and pulse rate in response to administered adrenaline and acetylcholine during hypoventilation were studied in urethane-anaesthetized rats. Hypoventilation was induced by decreasing the stroke volume of artificial ventilation from 1 ml/100 g to 0.3 ml/100 g. There was a significant rise in pulse rate accompanied by minimal changes in blood pressure during hypoventilation. The blood pressure and pulse rate in response to adrenaline were significantly reduced. The depressant effect of acetylcholine on pulse rate was intensified, but that on blood pressure was not significantly affected. These findings suggest that the compensatory cardiovascular reflexes may be impaired during hypoventilation.

Potentiation of depressor responses to arachidonic acid by angiotensin converting enzyme inhibitors in the rat

In chloralose anaesthetized rats, intravenous administration of captopril, SQ 20881, SA 446 or MK 421 (0.5 mg/kg) potentiated the depressor responses to arachidonic acid 3 mg/kg given intravenously. Same doses of the above angiotensin converting enzyme inhibitors caused an approximately 100-fold decrease in sensitivity to the pressor effects of angiotensin I, with a concomitant similar increase in sensitivity to the depressor effects of bradykinin. Depressor responses to arachidonic acid, both before and after administering the converting enzyme inhibitors, were abolished by intravenous indomethacin (5 mg/kg). These results suggest that increased synthesis of prostaglandins in the circulation may contribute to the hypotensive effect of the angiotensin converting enzyme inhibitors, a group of newly developed antihypertensive agents.

Effects of SK&F 93479 on experimentally induced ventricular arrhythmias in dogs, rats and mice

The effects of SK&F 93479, a potent histamine H2-receptor antagonist, on ventricular arrhythmias induced by coronary artery ligation in dogs and rats, and by aconitine infusion in mice were investigated. It was found that SK&F 93479 in large doses, significantly prevented the occurrence of spontaneous ventricular fibrillation and the changes in ventricular fibrillation threshold following coronary artery ligation in dogs. In rats subjected to ligation of the main left coronary artery, it significantly reduced the incidence of ventricular fibrillation, and significantly prolonged the time of onset of ventricular tachycardia and ventricular fibrillation. On the contrary, SK&F 93479 did not significantly alter the incidence or the time of onset of cardiac dysrhythmias caused by aconitine infusion in mice. These findings suggest that SK&F 93479 lacks non-specific antiarrhythmic activity and that its protective effects against coronary artery ligation may be mediated by its histamine H2-receptor antagonizing action. They also support the hypothesis that histamine may contribute to the genesis of ventricular arrhythmias resulting from acute myocardial ischaemia.

Protection by SK&F 93479 against the haemodynamic effects of coronary artery ligation in dogs

The effects of SK&F 93479, a potent histamine H2-receptor antagonist, on the changes in haemodynamics induced by coronary artery ligation were investigated in anaesthetized dogs. Intravenous bolus injection of SK&F 93479 1 mg/kg followed by 1 mg/kg/h infusion caused transient decreases in systemic blood pressure, left ventricular pressure, and dLVP/dtmax, but did not significantly alter heart rate. Coronary artery ligation produced haemodynamic depression, and this was significantly prevented by pretreatment of the animals with SK&F 93479. These findings suggest that histamine may contribute to the haemodynamic changes arising from acute myocardial ischaemia.

Decreased acid secretion and gastric lesion production by morphine in rats

The effects of graded doses of morphine on gastric secretion were studied in conscious rats with pyloric occlusion. It was found that, at doses which significantly prolonged the reaction time in the tail-immersion test, morphine significantly decreased both the volume and total acid output of gastric secretion. It was also observed that morphine produced gastric mucosal lesions in a dose-dependent manner. Pretreatment with naloxone 4 mg/kg significantly alleviated the gastric effects of morphine 32 mg/kg. It is suggested that the depressant effects of morphine on gastric secretion and the ulcerogenicity of the narcotic result from its stimulant activity on opiate receptors.

Morphine preference in rats previously morphine dependent

Morphine preference and tendency to relapse to morphine tolerance and dependence were studied in rats which were previously made morphine dependent. Tolerance to, and physical dependence on, morphine were initially produced by administration of increasing concentrations of morphine sulphate in 5% sucrose solution for 3 weeks. A test for drinking preference was performed 4 days after the rats had been successfully detoxified and showed no significant signs of morphine dependence. It was found that, while control animals drank only negligible amounts of morphine solution, previously morphine-dependent rats consumed significantly larger volumes of morphine solution and had recurrence of morphine tolerance and dependence. The present findings show that chronic administration of morphine in drinking fluid produces tolerance and physical dependence as well as addiction in rats; the latter definition is exemplified by these animals having a high tendency to relapse after successful drug withdrawal.

Effects of naloxone on serum corticosterone and gastric lesions in stressed rats

In rats subjected to restraint and exposure to cold, naloxone did not significantly influence the increased serum concentrations of corticosterone or the incidence of stress ulceration, but it significantly reduced the severity of gastric lesions. These findings suggest that endogenous opioids released during stress may contribute to the pathogenesis of stress ulceration. They also support the theory that the adrenocorticosteroids are unimportant aetiological factors in stress ulcer formation.

Antagonism of pentobarbitone-induced respiratory depression by naloxone in rats

The effects of naloxone, pentobarbitone, or their combination, on arterial blood gases were studied in urethane-anaesthetised rats. Naloxone itself did not significantly alter the blood gases. Pentobarbitone significantly decreased PO2 and elevated PCO2, and these effects were prevented by pretreatment with naloxone. Arterial blood pH was unaffected by any of the drugs. The findings suggest that naloxone lacks a specific analeptic effect, but can antagonise respiratory depression induced by pentobarbitone.

The lack of effect of histamine on spontaneous activity in the isolated human myometrium

The effects of histamine on the spontaneous activity of the isolated human myometrium were studied. Both the frequency and force of contractions of the muscle strips were not significantly altered by histamine. The presence of either a histamine H1- or H2-receptor antagonist in the organ bath did not significantly change the responses of the uterine muscle to histamine. These findings suggest that histamine has negligible effects on the human myometrium, possibly due to the absence, or paucity, of histamine receptors.

The production of ventricular arrhythmias in the guinea-pigs isolated heart using hypoxic perfusion fluids containing adrenaline

1. The effects of hypoxia, adrenaline perfusion, and their combination on cardiac rhythm were studied in the isolated perfused heart of the guinea-pig. 2. Hypoxia or adrenaline perfusion (5.5 mumol/l) produced a low incidence of ventricular arrhythmias (26% and 33%, respectively); however, the changes were not statistically significant. 3. A combination of hypoxia and adrenaline perfusion produced ventricular arrhythmias in each of twenty-three preparations: there were frequent ventricular premature contractions in eighteen preparations, and ventricular tachycardia or fibrillation in five preparations. The mean times of onset of these arrhythmias after hypoxia were 33.3 min (s.e.m. = 5.2) and 57.6 min (s.e.m. = 4.7), respectively. 4. The responsiveness of the frequent ventricular premature contractions to the antiarrhythmic effects of quinidine and lignocaine was tested in twelve preparations. Both drugs produced dose-dependent reductions in the percentage of ventricular ectopic beats. 5. These results suggest that a combination of hypoxia and adrenaline perfusion is a simple but reliable method of inducing ventricular arrhythmias in the isolated heart of the guinea-pig, and this provides a model that may be useful for the experimental evaluation of antiarrhythmic drugs.

Some observations on the gastric effects of phentolamine in rats

The effects of graded doses of phentolamine on gastric secretion, gastric emptying rate, gastric mucosal mucus content and gastric mucosal lesion incidence were studied in conscious rats 2 h after intramuscular administration. In pylorus-occluded rats, phentolamine (5, 10 or 20 mg/kg) produced dose-dependent decreases in the gastric secretory volume and total acid output. Similar doses of the drug also produced dose-dependent decreases in the gastric emptying rate in animals without pylorus occlusion (intact rats), but did not affect the gastric mucosal mucus content. The incidence of gastric mucosal lesions in pylorus-occluded or intact animals rose with increasing doses. The findings are discussed in the light of the possibility that phentolamine, in the dose range examined, possesses a sympathomimetic action which would underlie the gastric lesions observed.

Effects of zinc sulphate pretreatment on gastric acid secretion and lesion formation in rats infused intravenously with graded doses of methacholine

The effects of intraperitoneal pretreatment with zinc sulphate (22, 44 or 88 mg/kg) were studied on gastric acid secretion and lesion formation induced by methacholine (125, 250 or 500 microgram/kg/h) infused intravenously in rats with stomachs perfused in situ. Graded infusions of methacholine produced dose-dependent increases in gastric acid secretion and lesion incidence in saline-pretreated control rats. These effects were progressively reduced by increasing pretreatment doses of zinc sulphate. The relationship between these findings and the action of zinc on gastric mast cells is discussed.

The effect of zinc on anaphylaxis in vivo in the guinea-pig

The protective effects of pretreatment with zinc sulphate aerosols against bronchoconstriction induced by egg albumen or histamine aerosols were assessed in sensitized or non-sensitized guinea-pigs respectively. Pretreatment with an adequate concentration of zinc sulphate aerosol significantly prolonged the time of onset of bronchoconstriction in sensitized guinea-pigs challenged with egg albumen, but did not appreciably alter the onset time of histamine-induced bronchoconstriction in non-sensitized animals. These findings suggest that zinc aerosols may be of prophylactic value against bronchoconstriction of allergic origin.

The hemostatic effects of orally administered Yunnan Bai Yao in rats and rabbits

The effects of orally administered Yunnan Bai Yao were studied on the bleeding time in rats and the blood clotting time in rabbits. Significant decreases were seen in both the bleeding and clotting times, observed over a 4 h period following administration. These effects were seen as early as 1/2 h and were still present at 4 h. Graded doses of Yunnan Bai Yao produced dose-related decreases in blood clotting times in the rabbits. The findings suggest that some active principle, able to affect the hemostatic mechanism, is absorbed after oral administration of the herbal preparation.

Effects of zinc chloride on gastric secretion and ulcer formation in pylorus-occluded rats

The effects of 10-day pretreatment with i.p. injections of zinc chloride, 16 mg/kg, on gastric secretion and on gastric ulceration induced by stress or by acid accumulation were examined in pylorus-occluded rats. Zinc chloride pretreatment significantly reduced the volume of gastric secretion and the total acid output as well as the incidence of gastric ulcers induced either by stress or by acid accumulation. The findings support the idea zinc compounds may be useful in the treatment of gastric ulcers.

A study of the actions of histamine on the isolated rat heart

1. The effects of histamine on cardiac force, heart rate and coronary perfusion pressure were studied in the isolated rat heart, using the Langendorff perfused heart preparation. 2. Single injections of histamine induced dose-dependent decreases in contractile amplitude, heart rate and coronary perfusion pressure. 3. Perfusions of metiamide (above 1 x 10(-4) m) had a depressant effect on contractile force and heart rate, whereas diphenhydramine (4 x 10(-6) m) reduced only the heart rate. Both agents caused a fall in coronary perfusion pressure. 4. The negative inotropic and chronotropic effects of histamine on the isolated rat heart were not significantly influenced by either metiamide of diphenhydramine, or a combination of these drugs. However, the fall in coronary perfusion pressure induced by injections of histamine was significantly antagonized by metiamide or diphenhydramine. 5. These results suggest that the effects of histamine on the isolated rat heart may not be due entirely to stimulation of H1- or H2-receptors on the cardiac muscle cells. Evidence is presented for the existence of histamine H1- and H2-receptors in the coronary vessels.

Intragastric NaHCO3 perfusion and vagal-induced ulcer formation in the rat stomach

The effects of electrical vagal stimulation on gastric acid output and ulcer formation were studied in rats intragastrically perfused with saline or NaHCO3 solutions. Vagal stimulation produced a 100% incidence of glandular lesions and a significant increase in total acid output in saline-perfused stomachs. Antacid perfusion failed to prevent ulcer formation despite complete neutralization of the increased acid output. It is considered that vagal-induced gastric glandular lesions are not acid dependent.

Acute gastric ulcer formation in response to electrical vagal stimulation in rats

Intermittent electrical stimulation of the left cervical vagus increased intragastric pressure and induced a 100% incidence of haemorrhagic ulcers in the glandular mucosa of rat stomachs. Atropine pretreatment of sub-diaphragmatic vagotomy prevented these effects. The findings substantiate the idea that stress-induced glandular ulcers result from vagal-mediated increased gastric contractions.

The haemostatic effects of the Chinese herbal drug Yunnan Bai Yao: a pilot study

The effects of Yunnan Bai Yao on the bleeding time in rats and the blood clotting time in rabbits and man were studied. The medicinal preparation markedly shortened both the bleeding and clotting times; the decreases were significantly more intense than those inconsistently produced by starch or by starch with calcium. These preliminary findings suggest that the action of Yunnan Bai Yao appears not to be due to its pH (5.2) or to vasoconstriction, but other factors such as its calcium content or the physical effect of its particle size cannot yet be excluded.

The effects of metiamide on gastric secretion and stress ulceration in rats

The effects of metiamide, a histamine H2 blocker, on gastric secretion and ulcer formation in stressed pylorus-occluded rats were investigated. Metiamide, like atropine, significantly reduced the volume of gastric secretion and total acid output in unrestrained pylorus-occluded rats. Both drugs produced greater decreases in the volumes of gastric secretion in stressed rats than in their corresponding unrestrained groups. Stress itself reduced both parameters. Metiamide, like atropine, significantly reduced the incidence of gastric stress ulcers. When given together these two drugs did not provide greater protection. The results obtained with metiamide indicate that histamine plays a role in basal gastric secretion and in the pathogenesis of stress ulcers. As no correlation between gastric acid secretion and ulcer formation was demonstrated in this study, it is suggested that H2 receptors may also be involved in gastric motility. However, the possibility that metiamide could exert its ulcer-protecting effects through other mechanisms cannot yet be excluded.

Effects of stress and of autonomic blockers on gastric mucosal microcirculation in rats

Changes in gastric mucosal microcirculation in rats were studied by using the method of intra-aortic injection of India ink, followed by microdissection of the mucosa. Acute stress, induced by restraint and exposure to cold for 2 hr, caused marked and significant vasodilatation in the gastric mucosa. This vasodilatation was prevented by pretreatment with atropine or chlorpromazine, but not by alpha- or theta-adrenoceptor blocking agents. Phentolamine caused significant vasoconstriction in the gastric mucosa of non-stressed rats, but when animals were stressed phentolamine induced a greater vasodilatation than was obtained with stress alone. These observations provide added support for the hypothesis that stress induces vagal overactivity, probably of central origin. The resulting strong contractions of the gastric wall, and compression of the intramural vessels, are probably responsible for degeneration of the mucosal cells leading to the formation of stress-induced ulcers in the rat.