INHIBITORS OF HISTAMINE CATABOLISM AND THE ACTION OF GASTRIN IN THE RAT

Kolaviron attenuates ischemia/reperfusion injury in the stomach of rats

Kolaviron (KV), an active complex of at least 3 compounds in Garcinia kola seed, which is known for its antioxidant and anti-inflammatory activity, was investigated for its gastro-protective effect in the stomach of rats subjected to ischemia/reperfusion-induced gastric ulceration. Male adult Wistar rats (180-210 g) were randomized into 6 groups (n = 15) as follows: (i) control, (ii) ulcerated untreated (UU), (iii) KV alone (KVA), (iv) KV + ulcer (KVU), (v) ulcer + KV (UKV), and (vi) ulcer + omeprazole (20 mg/kg). Ulcer was induced through ischemia/reperfusion method after 2 weeks of daily oral KV (100 mg/kg). Rats were weighed daily, and gastric acid secretion, ulcer scores, hematological, biochemical, and histological variables were assessed 1 h after induction at 3 and 7 days post-ulceration. Body weight decreased in KVA (179.1 ± 1.6 g), and KVU (170.1 ± 2.2 g) compared with UU (199.0 ± 1.4 g). Gastric acid secretion decreased significantly in KVU after 1 h and 3 days post-ulceration (0.27 ± 0.03 mEq/L; 0.49 ± 0.02 mEq/L) compared with UU (0.60 ± 0.06 mEq/L; 0.85 ± 0.29 mEq/L), respectively. There was significant reduction in neutrophil/lymphocyte ratio of KVA (0.29 ± 0.06) and KVU (0.35 ± 0.02) compared with UU (0.54 ± 0.04). Malondialdehyde level decreased significantly with concomitant increase in anti-oxidative activities and nitric oxide level in the KV treated groups (KVA, KVU, UKV) compared with UU. In conclusion, treatment with KV protects the stomach by reducing gastric acid secretion, promoting antioxidant activity and suppressing action of reactive oxygen species.

The intestinal phase hormone

The existence of a stimulatory intestinal phase of gastric acid secretion has been suspected, but largely ignored, for many years. Recently, however, it has become clear that the intestinal phase plays an important role in acid production during digestion. The intestinal phase is of additional interest in relation to the profound gastric acid hypersecretion associated with portacaval shunt (PCS). Substantial evidence indicates that PCS-related gastric hypersecretion is due to unmasking of the intestinal phase by hepatic bypass of a humoral stimulant in portal blood that is normally degraded to a considerable extent by the liver. Studies in our laboratory during the past 12 years have provided strong physiologic evidence for humoral mediation of both the intestinal phase of gastric secretion and of PCS-related hypersecretion by a hormone that arises in the small intestine, particularly in the jejunum. Furthermore, our studies have demonstrated that this intestinal phase hormone (IPH) exists in humans as well as in dogs, rats, and pigs. Additionally, recent work by a number of investigators, as well as by our group, has provided convincing evidence that IPH is different from any of the known gastric stimulatory hormones. With these physiologic observations as a background, we have used a classical method for extracting acidic peptides to prepare a hog intestinal mucosa extract (HIME) that has all of the known physiologic properties of an IPH. Specifically, HIME contains a potent stimulant of gastric acid secretion that acts according to a linear dose-response relationship; that is not gastrin in any of its immunoassayable forms; that significantly augments the maximal acid secretory responses to pentagastrin, gastrin, CCK, and histamine; and that is substantially degraded by the liver, in contrast to gastrin and CCK. Efforts at isolating the gastric stimulatory substance in HIME suggest that it is a peptide of low molecular weight. Work directed at isolating IPH in pure form and identifying it is in progress.

Diamine oxidase activity in gastric and duodenal mucosa of man and other mammals with special reference to the pyloric junction

In the gastric mucosa of human subjects and of various mammals methylation was accepted as the main pathway of histamine catabolism. However, augmentation of gastric acid secretion by aminoguanidine, the strong inhibitor of diamine oxidase, indicated an influence of diamine oxidase activity on this secretory process. Therefore a careful reinvestigation of the occurrence of diamine oxidase activity was started from the distal duodenum in the direction of the cardia. In all species studied, diamine oxidase activity decreased from distal duodenum towards the pylorus. In dogs, landrace pigs and in human subjects the diamine oxidase activity clearly exceeded the pyloric borderline gradually becoming zero in corpus or fundus. In rabbits, however, and especially in mini-pigs no diamine oxidase activity was found beyond the pylorus. Among individuals gastric diamine oxidase activity showed a variable prevalence and could not be found regularly in all the subjects. In one patient with prepyloric ulcer a strong influence of pathophysiological processes on gastric diamine oxidase activity could be suspected. Thus, in every alteration of the gastric mucosa under experimental or clinical conditions also an alteration of gastric diamine oxidase activity should be taken into account.

The effect of the histidine decarboxylase inhibitor brocresine (NSD-1055) on gastric acid secretion in rats

The effect of the histidine decarboxylase inhibitor brocresine (NSD-1055) given by mouth, intraperitoneally or intravenously on tetragastrin-, histamine- and bethanechol-stimulated gastric acid secretion was examined in rats. Intravenous injection of brocresine slightly reduced the tetragastrin-stimulated secretion. Histamine-stimulated secretion was markedly increased by both intraperitoneal and intravenous injection of brocresine but it had no effect on the bethanechol-stimulated secretion. It was concluded that either histidine decarboxylase is not effectively inhibited by brocresine or any inhibition induced does not affect gastric acid secretion. The enhanced histamine-stimulated secretion points towards an inhibition of diamine oxidase by brocresine.

Comparative study of antral gastrin activity in some mammals

1. The amounts of crude gastrin extract and the gastrin activities of extracts from antral mucosa of several mammalian species have been determined.2. The yield of crude gastrin powder per gramme wet weight of antral mucosa was greater in goats and rabbits than in cat, dog, man or pig.3. Statistical differences do not appear to exist between the potencies of gastrin from the various species. The potencies of the powders were within the ranges 1.2-1.8 mug porcine gastrin II/mg with the exception of the extract from frozen dog antra (0.8 mug/mg).4. During prolonged freezing of animal antra and consequent thawing before extraction, significant losses in gastrin activity occurred in the dog.5. The amounts of gastrin activity per gramme wet weight of antral mucosa from herbivores (goat, rabbit and cattle) were greater than those from non-herbivores (cat, dog, man and pig).

Rat gastric acid secretion studies with histamine and synthetic gastrin-like pentapeptide

1. Gastric acid secretion was measured in the urethane anaesthetized rat whilst maintaining a recirculated gastric perfusion fluid at pH 4.2. The latent period of onset of secretion following single intravenous doses of histamine and pentapeptide in combination was significantly shorter than that following either stimulant alone.3. When administered over a period of 2 hr the maximal steady rate of secretion in response to pentapeptide was 75% of that to histamine.4. Acid stimulatory effects were additive both when the drugs were given concurrently over a 2 hr period and when one was administered after a maximal response had been obtained to the other.5. Although there is some evidence to indicate that histamine and pentapeptide might be initiating acid secretion by different mechanisms it is suggested that they may not be acting with total independence.

Sex hormones, and acid gastric secretion induced with carbachol, histamine, and gastrin

This study confirms previous reports that satisfactory gastric acid secretory responses to intravenous administration of histamine, carbachol, and gastrin can be obtained. Bilateral castration of the male rats significantly reduced acid gastric secretory responses to carbachol but not to histamine. Overiectomized rats treated with 17B-oestradiol (short-term treatment) showed a statistically significant reduction in gastric acid secretion induced with all the secretagogues, but the results when rats were treated with testosterone were inconsistent. In animals given gastrin or histamine gastric acid secretion was reduced and was of statistical significance with gastrin (0.02 < p < 0.05) but not with histamine (0.05 < p > 0.1). It is concluded that a high oestrogen blood level is capable of inhibiting effectively acid gastric secretion in both sexes except that a higher level of blood oestrogen is required in the male. The results showed further that of all the sex hormones used, only oestrogen had a significant effect on gastric acid secretion.

Effect of hepatic transit of gastrin, pentagastrin, and histamine measured by gastric secretion and by assay of hepatic vein blood

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Effect of glycopyrronium bromide on basal, and histamine- or gastrin-induced gastric secretion

Acid secretory responses were obtained in rats given either intravenous histamine as dihydrochloride or gastrin subjected to partial purification. A continuous recording method for measuring gastric acid secretion was used. When the rat stomach was perfused with weak sodium hydroxide solution, glycopyrronium bromide (a powerful anticholinergic drug) blocked the acid gastric secretory effects of both histamine and gastrin. Glycopyrronium bromide in doses of 2 μg/100 g body weight of rat is well tolerated. Doses higher than 2 mg/100 g caused respiratory disturbances. The action of glycopyrronium bromide in blocking the gastric secretory effects of gastrin supports the hypothesis that gastrin acts partly by stimulating the vagus nerve.

The actions of caerulein on gastric secretion of the dog and the rat

1. Caerulein, as expected from its amino-acid composition and sequence, has a potent stimulant action on gastric secretion in the dog, the rat and the frog.2. In the denervated fundic pouch of the dog, caerulein increases the rate of flow of gastric juice and the outputs of acid and pepsin. Acid concentration and pepsin concentration in caerulein-produced juice are generally greater than in control juice. The threshold subcutaneous dose of caerulein is 0.15-0.5 mug/kg and the threshold rate of intravenous infusion 0.25-0.5 mug/kg per hr. Rapid intravenous injection is ineffective. On a molar basis, caerulein is approximately twice as active as human gastrin I on volume and acid output of the gastric pouch and 4 times as active on pepsin output.3. Sustained acid secretion of the fundic pouch produced by histamine infusion is inhibited by caerulein, administered either intravenously or subcutaneously. In turn, acid secretion elicited by caerulein is inhibited by atropine.4. In the rat, the activity ratio of caerulein to human gastrin I is 7-30, calculated on a molar basis, and is thus considerably greater than in the dog. Further, caerulein is 3 times more active than cholecystokinin-pancreozymin. Tested on the perfused stomach preparation of the rat, the threshold dose of caerulein by rapid intravenous injection is 25 ng/kg, by intravenous infusion 0.25 mug/kg per hr, and by subcutaneous injection 0.25 to 0.5 mug/kg.5. The activity of caerulein is sharply reduced by pretreatment of the rats with the histamine liberator 48/80 and potentiated by pretreatment with the diamine oxidase inhibitor aminoguanidine. When caerulein is given by rapid intravenous injection during a priming infusion of histamine its effect is enhanced and considerably prolonged.6. The isolated mucosa of the frog stomach is extremely sensitive to caerulein which, in a concentration of a few pg/ml., stimulates active transport of chloride.7. Qualitative and quantitative differences in the action of gastrin and caerulein are pointed out, and particular emphasis is laid on the importance of esterification of the tyrosyl residue for the biological activity of caerulein.

Effect of decreased levels of endogenous gastric tissue histamine on acid secretion and stress ulcer formation in the rat

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