Hiromichi Niida

Role of prostaglandin deficiency in pathogenetic mechanism of gastric lesions induced by indomethacin in rats.

The present study was undertaken in rats using 2-deoxy-D-glucose (2DG) as a stimulator of gastric motility and a low dose of indomethacin as a prostaglandin (PG) synthesis inhibitor to investigate the roles of gastric motility and PG deficiency in the pathogenesis of indomethacin-induced gastric lesions. Subcutaneously administered indomethacin at 5 mg/kg did not induce any visible damage in the mucosa within 4 hr, but at 25 mg/kg produced linear hemorrhagic lesions along the long axis of the stomach. 2DG (100 mg/kg/hr), given intravenously, produced linear nonhemorrhagic lesions along the mucosal folds and, in the presence of 5 mg/kg of indomethacin, caused severe hemorrhagic lesions in the same areas of the stomach. Gastric motility was markedly enhanced by both indomethacin (25 mg/kg) and 2DG, while acid output and mucosal blood flow were increased only by the latter. Mucosal PGE2levels were significantly reduced by indomethacin (25 mg/kg) but not by 2DG. Indomethacin at 5 mg/kg alone had no or little effect on any parameter except PG levels, which were reduced to similar degrees as caused by 25 mg/kg of the agent. Time-course development of the lesions was closely associated with those changes in gastric motility after administration of indomethacin (25 mg/kg) and 2DG. These results suggest that the enhanced gastric motility is, by itself, sufficient to induce damage (nonhemorrhagic) in the mucosa and that a PG deficiency alone does not induce any damage but is required for further extension to hemorrhagic lesions of nonhemorrhagic ones that are initially induced by enhanced gastric motility.

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.

Vagally mediated acid hypersecretion and lesion formation in anesthetized rat under hypothermic conditions

The pathophysiological changes associated with hypothermia were investigated in the rat stomach under anesthetized conditions. The animal was placed in a styrene foam box and the core body temperature was kept between 24 and 36°C using a heat lamp and refrigerant pack. Lowering of body temperature (<30°C) produced acid hypersecretion and induced hemorrhagic lesions in the gastric mucosa; these responses reached the maximum at 28°C, and a significant relationship was found between acid output and lesion score. Hypothermia (28°C) also caused a marked increase of gastric contractile activity and mucosal blood flow (MBF), but the ratio of acid output to MBF became greater when compared to that obtained under normothermic conditions. These changes induced by hypothermia (28°C) were completely blocked by vagotomy and were significantly inhibited by atropine, hexamethonium, clonidine, or TRH antiserum. However, lowering body temperature did not significantly affect acid secretory, motility, and ulcerogenic responses induced by carbachol in the vagotomized rat, excluding local mechanisms (suppression of the inhibitory nerves) in the hypothermia-induced changes. We conclude that hypothermia alone stimulates vagally dependent acid secretion and motility, resulting in damage in the gastric mucosa. These changes may be centrally mediated by TRH, which is released in association with the thermogenic response to hypothermia.

Possible mechanisms involved in gastric hypermotility caused by indomethacin in the rat

Pathogenesis of indomethacin-induced gastric lesions was investigated in the rat by measuring lesions, gastric motility, and terminal blood glucose levels and correlating them with each other. Subcutaneously administered indomethacin (3–25 mg/kg) dose-dependently produced lesions in the stomach with concomitant gastric hypermotility and reduction of blood glucose levels. When the lesion score and the motility were plotted against terminal glucose levels, a highly significant relationship was found among these three factors (P < 0.01). Gastric lesions and hypermotility induced by indomethacin (25 mg/kg) were suppressed significantly by 16,16-dmPGE2 (10 Μg/kg) with no effect on the glucose levels, while intravenous infusion of glucose (25% w/w, 1.4 ml/hr) prevented these responses and restored the reduced glucose levels above the basal values. In addition, both 16,16-dmPGE2 and glucose infusion afforded a significant protection against gastric lesions induced by indomethacin even in the acid-perfused stomach (150 mM HCl). These results confirmed gastric hypermotility as a key element in the pathogenesis of indomethacin-induced lesions and further suggested that indomethacin may sensitize gastric contractility through glycoprivic receptors by inducing hypoglycemia and PG deficiency.

Influences of urethane anesthesia on indomethacin-induced gastric mucosal lesions in rats : relation to blood glucose levels

Effects of urethane on gastric motility and mucosal ulcerogenic responses induced by indomethacin were investigated in the rat in relation to blood glucose levels (BGL) and compared with those of pentobarbital Na. Urethane (1.25 g/kg) given intraperitoneally, caused a progressive and significant rise in BGL, while pentobarbital (30 mg/kg) given intraperitoneally did not affect BGL. Subcutaneous administration of indomethacin (25 mg/kg) caused high-amplitude gastric contractions and induced hemorrhagic lesions in the stomachs of conscious rats. These lesions were significantly inhibited by urethane but not pentobarbital. Administration of urethane abolished basal gastric motility and almost completely suppressed the motility responses induced by indomethacin, while pentobarbital did not have much effect on gastric motility under basal and indomethacin-stimulated conditions. Acid secretion was significantly decreased by urethane and increased by pentobarbital. Pretreatment of the animals with yohimbine (5 mg/kg, subcutaneously) but not prazosin (0.5 mg/kg) inhibited the elevation in BGL seen after administration of urethane and allowed resumption both gastric motility and ulcerogenic responses induced by indomethacin, with less change in acid secretion. These results suggest that intraperitoneal administration of urethane prevented indomethacin-induced gastric lesions, probably by inhibiting the enhanced gastric motility response, and this effect may relate to its hyperglycemic action mediated by α2-adrenoceptors. These findings also provide further evidence to support the importance of gastric motility in the pathogenesis of these lesions.

Dual Effects of N-Ethylmaleimide on Ethanol-Induced Gastric Lesions in Rats

The effects ofN-ethylmaleimide (NEM), a sulfhydryl (SH) blocker, on ethanol-induced gastric lesions were investigated in rats by varying the route of administration. Oral administration of acidified ethanol (60% ethanol in 150 mM HCl, 1 ml) produced hemorrhagic bandlike lesions in the gastric mucosa. Pretreatment of the animals with orally administered NEM (0.1–10 mg/kg) dose-dependently inhibited these lesions (the inhibition was over 80% at 1mg/kg or greater) and the effects were partially reversed by indomethacin (5 mg/kg, subcutaneous). However, when NEM (10 mg/kg) was given subcutaneously, this agent significantly worsened the lesions. Intragastrically applied NEM produced a dose-dependent reduction of the transmucosal potential difference (PD) and the mucosal nonprotein SH levels, an, increase of the volume of gastric contents, and an inhibition of gastric motility, while these parameters remained unaltered after subcutaneous administration of the agent. The microvascular permeability in the mucosa was significantly increased by both oral and subcutaneous administration of NEM (10 mg/kg) but remained unchanged in response to lower doses of orally administered (<3 mg/kg). These results suggest that NEM given orally is cytoprotective, to the stomach against ethanol, probably by acting as a mild irritant and due to dilution of an irritant and inhibition of gastric motility (muscle relaxation), but when given subcutaneously it aggravates the lesions by unknown mechanisms.

Effects of TY-10957, a Stable PGI2 Derivative, on Gastroduodenal Lesions and Secretory Responses in the Rat

The effects of TY-10957, a stable PGI2 derivative, on gastroduodenal lesions and secretory responses were examined in rats and compared with those of ornoprostil, a PGE1 derivative. Orally administered TY-10957 dose dependently prevented gastric lesions induced by ethanol/HC1 (60% ethanol in 150 mM HCl) and duodenal ulcers induced by mepirizole (200 mg/kg); a significant effect was obtained at 3 micrograms/kg or greater in the former and at 300 micrograms/kg in the latter. Intraduodenally administered TY-10957 had minimal effects on gastric acid secretion, and at the highest dose (300 micrograms/kg) both the basal acid output and that stimulated by histamine (20 mg/kg) were significantly reduced by about 40%. TY-10957 (30-300 micrograms/kg s.c.) produced a marked increase of alkaline secretion in both stomach and duodenum of anesthetized rats, and these effects were significant at 30 micrograms/kg in the stomach and at 100 micrograms/kg in the duodenum. On the other hand, ornoprostil produced a potent and significant inhibition against ethanol/HCl-induced lesions (greater than 1 microgram/kg), but had no effect on mepirizole-induced duodenal ulcers. This PGE1 derivative had no influence on both basal and stimulated acid secretion and did not significantly affect alkaline secretion even at 100 micrograms/kg. These results suggest that TY-10957 has a protective action on both gastric and duodenal mucosa. The mechanism of duodenal antiulcer effect may involve both inhibition of acid and stimulation of alkaline secretion, while the gastroprotective action of this agent may be attributed to other factors.

Determination of gastroduodenal alkaline responses in the rat

We set up a new system for measuring the gastroduodenal HCO3- responses using pH change and potential difference (PD) in the anesthetized rat. The stomach or the proximal duodenum was perfused at the flow rate of 0.7 mL/min with saline (pH 4.5), the pH of the perfusate and PD were continuously monitored, and HCO3- output was determined by back-titrating the perfusate and by measuring the area of pH change. In the case of the stomach, acid secretion was inhibited by omeprazole (60 mg/kg, i.p.). Output of both pH and HCO3- in these tissues was significantly increased by intravenous administration of prostaglandin (PGE2), 16, 16-dimethyl PGE2, carbachol, and YM-14673 (a thyrotropin-releasing hormone (TRH) analog), whereas the PD responded to these agents by a significant rise in the duodenum and decrease in the stomach. These parameters also responded to physiological stimulation such as mucosal acidification. When the area of pH change caused by various agents was plotted against the net amount of HCO3- output determined from back-titration, a significant relationship was found between these two factors (r = 0.98). These results indicate that this system using pH change may be useful for quantitative determination of HCO3- response in the gastroduodenal mucosa.

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.