Hideyuki Nishiwaki

Repair of Mucosal Damage Induced by Ethanol in the Rat Stomach

We investigated the relationship between the severity of acute injury and the rapidity of mucosal repair in stomachs of anesthetized rats, and examined the influence of prostaglandins (PGs) on the process of restoration. Different degrees of mucosal damage were produced using ethanol and by varying the concentration (5-100%) and the exposure period (1-60 min). Exposure of the stomach for 10 min to ethanol induced hemorrhagic lesions and a reduction in the transmucosal potential difference (PD); its severity and its magnitude were increased in a concentration-related manner. After removal of ethanol, the reduced PD recovered quickly in the case of 5-25% ethanol, but it normalized slowly or did not show any recovery in the case of 50 or 100% ethanol, respectively. Histologically, ethanol at 5-25% produced various degrees of damage in the superficial epithelial cells, while the damage was deeper into the mucosa beyond the basal lamina after exposure to ethanol at 50% or greater. Similar phenomena were observed after exposure to 50% ethanol for various periods; the rapidity of PD recovery and mucosal restoration was faster when the exposure period was less than 2 min, and these parameters became slower as it was increased. Moreover, the PD recovery was significantly expedited or delayed, respectively, by 16,16-dimethyl PGE2 (30 micrograms/kg) or indomethacin (5 mg/kg), and the former counteracted the inhibitory effect of indomethacin. These results suggest that the process of mucosal regeneration may largely depend on the severity of damage initially formed, and probably involves factors sensitive to endogenous PGs.

Bilateral adrenalectomy worsens gastric mucosal lesions induced by indomethacin in the rat: Role of enhanced gastric motility

The mechanism by which bilateral adrenalectomy worsens indomethacin-induced gastric lesions was investigated in rats. In sham-operated rats subcutaneously administered indomethacin produced gastric lesions at doses of 10 mg/kg body wt or greater, in association with lowering of blood glucose levels. In a parallel study, indomethacin induced gastric hypermotility at the same dose levels but had no effect on acid output or mucosal blood flow even at 25 mg/kg body wt. Adrenalectomy (2 wk) itself significantly reduced the blood glucose levels (approximately 50%) and markedly potentiated the ulcerogenic and motility responses caused by indomethacin; the ED50 values dropped to approximately 10 times lower than those in sham-operated rats. Both acid output and mucosal blood flow were significantly reduced by adrenalectomy, but these values were increased after indomethacin treatment (3 mg/kg body wt). The ulcerogenic and motility responses caused by indomethacin were significantly reduced by acute infusion of glucose (25% wt/wt, 1.2 ml/h) intravenously in both sham-operated and adrenalectomized rats, and by subcutaneous administration of hydrocortisone acetate (10 mg/kg body wt for 2 wk) in the latter group. When the motility and the ulcer score were determined in the same animals, a highly significant relationship was found between these two factors in both sham-operated and adrenalectomized rats. These results suggest that (a) the increased gastric motility may be a key element in the pathogenesis of indomethacin-induced lesions and in the mechanism for aggravation of the lesions and in the mechanism for aggravation of the lesions by adrenalectomy, and (b) abrasion of adrenal glands by inducing hypoglycemia may sensitize the system to indomethacin and increase gastric motility.

16,16-Dimethyl prostaglandin E2 aggravates gastric mucosal injury induced by histamine in rats

Histamine dihydrochloride (40 or 80 mg/kg, dissolved in 10% gelatin) subcutaneously administered to fasted rats induced few lesions in the gastric mucosa within 4 h. Pretreatment with subcutaneously administered 16,16-dimethyl prostaglandin E2 (dmPGE2; greater than or equal to 10 micrograms/kg) dose-dependently worsened mucosal injury induced by histamine, mostly with severe hemorrhage in the corpus mucosa along the greater curvature, although dmPGE2 alone did not induce any macroscopic damage. The mucosal vascular permeability as measured using Evans blue was slightly but significantly augmented by either dmPGE2 (30 micrograms/kg) or histamine (80 mg/kg) alone, but was markedly increased by histamine in the presence of dmPGE2. The increased vascular permeability occurred within 2 h, and preceded the appearance of hemorrhagic mucosal injury. Both the mucosal injury and the increased vascular permeability caused by histamine (80 mg/kg) in the presence of dmPGE2 (30 micrograms/kg) were significantly reduced by pretreatment with tripelennamine (30 mg/kg) and prednisolone (3 mg/kg), but not affected by atropine sulfate, cimetidine, methysergide, or indomethacin. The stimulation of acid secretion caused by histamine was significantly inhibited by dmPGE2 (30 micrograms/kg). Repeated administration of histamine (40 or 80 mg/kg) in the same area of the stomach in the presence of dmPGE2 (30 micrograms/kg), once or twice daily for 4 days to fed rats, induced more pronounced damage than single-dose treatment. These results suggest that dmPGE2 may aggravate gastric mucosal injury induced by histamine in rats probably due to potentiation of the increased vascular permeability caused by histamine through stimulation of H1-receptors.

Effect of lafutidine, a novel histamine H2-receptor antagonist, on monochloramine-induced gastric lesions in rats: role of capsaicin-sensitive sensory neurons.

Background : Lafutidine ((±)‐2‐(furfurylsulfinyl)‐N‐(4‐(4‐(piperidinomethyl)‐2‐pyridyl)oxy‐(Z)‐2‐butenyl)acetamide) is a novel histamine H2‐receptor antagonist and has been shown to exhibit a potent gastroprotective activity in addition to its antisecretory action. In the present study, we examined the effects of lafutidine on the mucosal ulcerogenic and potential difference (PD) responses induced by monochloramine (NH2Cl) in rat stomachs.

Effects of dopamine on gastric mucosal lesions induced by ethanol in rats

Acidified ethanol (60% ethanol in 150 mM HCl, per os) induced elongated bands of hemorrhagic lesions along the long axis of the stomach within 1 hr in rats. Pretreatment with dopamine hydrochloride (DA: 1–10 mg/kg, subcutaneously) dose-dependently reduced the severity of these lesions. In parallel study, DA had no effect on acid secretion but inhibited gastric motor activity in a dose-related manner. The inhibitory effects of DA on both acidified ethanol-induced lesions and gastric motor activity were significantly reversed by pretreatment with yohimbine, an inhibitor of α2-adrenoceptors (5 mg/kg, subcutaneously), but not by prazosin, haloperidol, or indomethacin. Similar to DA, both norepinephrine (NE: 1 mg/kg, subcutaneously) and epinephrine (EPI: 1 mg/kg, subcutaneously) showed inhibition of the motor activity and gastroprotection against acidified ethanol, but these effects were also significantly attenuated by yohimbine. A highly significant relationship was found between the inhibitory effects of DA, NE, and EPI on the motor activity and the mucosal lesions (r=0.8577, P<0.05). In addition, administration of gentian violet (0.5% w/v, per os) stained the mucosa deep blue as elongated wide bands in the corpus region, and such localized staining was significantly prevented by DA, suggesting a flattening of the mucosal foldings in the presence of DA. These results suggest that DA (and other catecholamines) protects the rat gastric mucosa against injury caused by acidified ethanol, probably through inhibition of gastric motor activity mediated with stimulation of α2-adrenoceptors.

Role of local motility changes in the pathogenesis of duodenal ulcers induced by cysteamine in rats

The possible role of local motility in the pathogenesis of duodenal ulcers was investigated in rats using cysteamine. Duodenal motor activity was measured as intraluminal pressure recordings by means of a balloon positioned in the proximal duodenum. Subcutaneous administration of cysteamine (100 mg/kg) produced two linear bandlike lesions in the proximal duodenum within 6 hr. This dose of cysteamine significantly increased gastric acid secretion in acute fistula rats, and decreased duodenal HCO3− secretion caused by acid. During this period, this agent inhibited gastric motility but did produce markedly enhanced contractions in the duodenum. The changes in duodenal motility appeared within 5–10 min and were dose-dependent for cysteamine (10–100 mg/kg). Pretreatment with subcutaneously administered atropine (10 mg/kg), 16,16-dmPGE2 (30 μg/kg) or dopamine (10 or 30 mg/kg) significantly reduced the development of duodenal lesions caused by cysteamine, the inhibition being 86.8%, 49.7%, 54.5% or 67.8%, respectively. In the presence of cysteamine, dopamine had minimal effect on both acid and HCO3− secretion, while atropine or 16,16-dmPGE2 markedly inhibited acid secretion or increased HCO3− secretion, respectively. The enhanced duodenal motility induced by cysteamine was blocked partially by atropine and only slightly by 16,16-dmPGE2. Dopamine showed a dose-dependent inhibition on the duodenal hypermotility following cysteamine, and at 30 mg/kg almost completely abolished the development of contractions. These results suggest that abnormal hypermotility in the duodenum may be partly involved in the pathogenesis of cysteamine-induced duodenal ulcers.

Analysis of pathogenic elements involved in gastric lesions induced by non-steroidal anti-inflammatory drugs in rats

Pathogenesis of gastric damage induced by non‐steroidal anti‐inflammatory drugs (NSAID) involves multiple elements, such as deficiency of prostaglandins (PG), gastric hypermotility, neutrophil activation and luminal acid. The present study was performed to examine the effects of these elements, either alone or in combination, on the rat gastric mucosa and investigate which element is most closely associated with the gastric ulcerogenic response to NSAID. The following treatments were used to express various pathogenic elements: (i) a low dose of indomethacin (IM) to cause PG deficiency; (ii) 2‐deoxy‐D‐glucose (2DG) to induce gastric hypermotility and acid secretion; (iii) histamine to induce acid hypersecretion; and (iv) n‐formyl‐Met‐Leu‐Phe (fMLP) to elicit neutrophil activation. When rats fasted for 18 h were subjected to each treatment alone, only 2DG caused slight macroscopic damage in the gastric mucosa within 4 h. Indomethacin showed over 90% inhibition of mucosal PG generation and fMLP increased myeloperoxidase activity four‐fold greater than normal values, yet either of these treatments alone did not cause any damage in the stomach. However, the combination of IM with 2DG or His provoked severe lesions in the stomach or the duodenum, respectively, while fMLP did not modify or potentiate the mucosal ulcerogenic response to other treatments. We conclude that among various pathogenic elements only gastric hypermotility is sufficient, by itself, to induce mild damage in the mucosa, that PG deficiency may be critical in the increase of mucosal susceptibility to injury and that neutrophil activation alone is not ulcerogenic in the gastric mucosa nor does it potentiate the ulcerogenic effect of other elements. Luminal acid may be a prerequisite for later extension of damage to severe lesions.

Effects of gastric distension and prostaglandin on acid ethanol-induced mucosal lesions in the rat

The effects of gastric distension on the morphology of acidified ethanol (AE) -induced mucosal lesions and on the protective action of 16,16-dm PGE2 were investigated in rats. AE (50% ethanol in 150 mM HCl) was given by gavage in the intact stomach or through a fistula prepared in the forestomach in the pylorus-ligated stomach. AE produced elongated bands of hemorrhagic necrosis within 1 hr in the former, while in the pylorus-ligated stomach the shape of lesions varied depending upon the volume of irritant. One milliliter produced bandlike lesions, whereas 2 ml or more induced widespread lesions; such volumes were observed to remove the mucosal folds. 16,16-dm PGE2 (0.3–10 μg/kg, subcutaneous) dose dependently reduced bandlike lesions in the intact stomach, but had no or little effect on non-band-like lesions in the pylorus-ligated stomach. This agent (10 μg/kg) had a slight effect on the reduction of PD caused by 10-min exposure of the stomach to AE (2 ml) in the intact stomach, while such effects were not apparent in the pylorus-ligated stomach. Oral gentian violet (2 ml, 0.3% w/v) produced bandlike staining of the mucosa in intact rats, but the effect was blocked by pyloric ligation. 16,16-dm PGE2 also significantly prevented the localized staining pattern seen in intact rats. These results suggest that (1) the bandlike pattern of AE-induced injury is dependent on the presence of mucosal folds (distending the stomach abolishes mucosal folds and widespread injury results); (2) 16,16-dm PGE2 prevented the fold-related, bandlike lesions and bandlike staining of the mucosa, but failed to abolish the generalized lesions; and (3) PG cytoprotection appears associated with the formation of bandlike lesions which are dependent on the presence of mucosal folds.

Body temperature-dependent action of baclofen in rat stomach

The effect of baclofen (PCPGABA) on acid secretion, motility, and mucosa was investigated in the anesthetized rat stomach under various body temperatures (BT: 28–38° C), and they were compared with those of 2-deoxy-d-glucose (2DG), an acid stimulant through cytoglycopenia. Under these conditions PCPGABA induces lesions dose-dependently (>1 mg/kg, subcutaneously) in both the stomach and duodenum, and this action was dependent on BT; lowering of BT enhanced the ulcerogenicity. PCPGABA (3 mg/kg) had no effect on acid secretion at higher BT (36–38° C) but produced a marked increase of acid output at lower BT (30–32° C). 2DG caused a stimulation of acid output and gastric lesions without BT dependency, but the duodenal ulcerogenicity enhanced at lower BT. Gastric motility was enhanced significantly by these two agents to similar degrees, at either high or low BT. Neither PCPGABA nor 2DG affected alkaline secretion in the duodenum, while lowering of BT by itself reduced alkaline secretory responses. The above changes caused by PCPGABA and 2DG were blocked by both atropine and vagotomy. These results suggest that (1) acid stimulatory and ulcerogenic action of PCPGABA may involve a temperature-dependent process but does not relate to a cytoglycopenia, and (2) the vagus nerve mediating acid secretion and motility may be different in the temperature dependency.

Different effects of cytoprotective drugs on ethanol- and aspirin-induced gastric mucosal injury in pylorus-ligated rats

In anesthetized rats oral administration (2 ml) of both ethanol (50% in 150 mM HCl) and aspirin (80 mM in 150 mM HCl) produced bandlike lesions in the stomach, while more generalized lesions occurred in the pylorus-ligated stomach when the irritant was given intragastrically through the fistula prepared in the rumen and the mucosal folds were removed by stomach distension. The bandlike lesions induced in the intact stomach by both irritants were significantly and dose-dependently prevented by 16,16-dimethyl PGE2 (dmPGE2: 3 and 10 μg/kg, subcutaneously), cysteamine (30 and 100 mg/kg, subcutaneously) or timoprazole (10 and 30 mg/kg, per os) at the doses which significantly inhibited gastric motility. In the pylorus-ligated stomach, however, neither of these agents showed any protection against the generalized lesions induced by ethanol, but such lesions caused by aspirin were significantly prevented only by dmPGE2. These agents also showed similar effects against the reduction of transmucosal PD in the pylorus-ligated stomach exposed to ethanol and aspirin. These results suggest that (1) the formation of bandlike lesions caused by ethanol and aspirin depends on the presence of mucosal folds and may be prevented by the agents that inhibit gastric motility, (2) the pathogenesis of the lesions induced by aspirin and ethanol may be different in the pylorus-ligated stomach, and (3) dmPGE2 has a unique protective ability that is not shared by usual cytoprotective agents.