Capsaicin and papaverine are potent vasorelaxants with strong gastroprotective activity against damage induced by absolute ethanol. This protection was originally attributed to the increase in gastric mucosal blood flow (GBF) and the present study was designed to determine the possible role of nitric oxide (NO) and prostaglandins (PG) in the protective and hyperemic effects of capsaicin and papaverine on rat gastric mucosa. We found that the pretreatment with capsaicin (0.1-0.5 mg/kg i.g.) or papaverine (0.1-2 mg/kg i.g.) reduced dose dependently the area of ethanol-induced lesions, the ED50 being 0.3 and 1 mg/kg, respectively. This protection was accompanied by a gradual increase in the GBF. Intravenous injection of Nω-nitro-L-arginine (L -NNA; 1.2-5 mg/kg), a selective blocker of NO synthase, which by itself caused only a small increase in ethanol lesions, reversed dose dependently the protective and hyperemic effects of capsaicin and papaverine against ethanol-induced damage and attenuated the increase in GBF induced by each of these agents alone. This deleterious effect of L -NNA on the gastric mucosa and the GBF was fully antagonized by L -arginine (200 mg/kg i.v.) but not by D-arginine. L -arginine partly restored the decrease in GBF induced by L -NNA. Pretreatment with indomethacin (5 mg/kg i.p.), which suppressed the generation of PG by 85%, slightly enhanced the mucosal lesions induced by ethanol but failed to affect the fall in GBF induced by this irritant. Gastroprotective and hyperemic effects of capsaicin and papaverine were partly reversed by indomethacin suggesting that endogenous PG are also implicated in these effects. Addition of L -NNA to indomethacin completely eliminated both the protective and hyperemic effects of capsaicin and papaverine. We conclude that both NO and PG contribute to the gastroprotective and hyperemic effects of capsaicin and papaverine on the gastric mucosa.
Epidermal growth factor (EGF) has been reported to stimulate epithelial cell proliferation and to inhibit gastric H+ secretion, but no details of the latter effect have been studied. This paper reports the effects of EGF on gastric and pancreatic secretions induced by various stimulants in vivo on conscious dogs and in vitro on isolated rabbit gastric glands. EGF was found to be an effective inhibitor of H+ secretion induced from the fully innervated and vagally denervated portions of the stomach stimulated by secretagogues activating receptors of the parietal cells (pentagastrin, histamine, and urecholine) and by natural stimulants such as sham or ordinary feeding. It appears to act directly on the parietal cells, as the inhibitory effect in vivo was not accompanied by any change in postprandial serum gastrin level. In addition, EGF was found to suppress H+ formation in the isolated gastric glands, both under resting conditions and after stimulation with histamine, carbachol, or dibutyryl cAMP. EGF failed to affect pancreatic response to exogenous hormones (secretin and cholecystokinin) but reduced postprandial secretion probably because of inhibition of H+ secretion from the subsequent reduction in duodenal acid loads. We conclude that EGF is a potent, specific, and direct inhibitor of H+ secretion from the parietal cells and that it does not affect alkaline gastroduodenal or pancreatic secretion.
To determine whether prostaglandin exerts a direct action on individual gastric epithelial cells that protects them from ethanol-induced injury, dispersed chief cells from guinea pig stomach were pretreated with 16,16-dimethyl-prostaglandin E2 (dmPGE2) or placebo before incubation with ethanol or control. Cell injury was assessed in terms of exclusion of Fast Green dye, release of lactate dehydrogenase, alterations of ultrastructure, and pepsinogen secretion stimulated by a variety of secretagogues. Of chief cells 60 +/- 2% were stained by Fast Green if incubated with 10% ethanol for 1 h after pretreatment with placebo, whereas only 38 +/- 1% of cells showed Fast Green staining when pretreated with 2.6 microM dmPGE2 before ethanol exposure. Similarly, 63 +/- 2% of cellular lactate dehydrogenase was released from chief cells pretreated with placebo compared with 36 +/- 4% of lactate dehydrogenase released from cells pretreated with 2.6 microM dmPGE2 (P less than 0.01). The prostaglandin's protective effect persisted throughout a 6-h incubation with ethanol. Scanning and transmission electron micrographs demonstrated disintegration of chief cells pretreated with placebo before ethanol exposure, whereas ultrastructural architecture was relatively preserved among chief cells pretreated with dmPGE2. Preincubation with 8 or 10% ethanol inhibited the subsequent stimulation of pepsinogen secretion caused by carbachol, cholecystokinin, A23187, 12-O-tetradecanoylphorbol 13-acetate, forskolin, or 8-bromoadenosine 3',5'-cyclic monophosphate. Pretreatment with dmPGE2 did not reduce the ethanol-induced inhibition of secretion stimulated by any of these secretagogues. These data indicate that dmPGE2 significantly reduces ethanol-induced damage to dispersed chief cells in terms of alterations of membrane permeability and ultrastructure but does not prevent the ethanol-induced impairment of pepsinogen secretion. These findings provide evidence that dmPGE2 exerts a direct but limited protective action on the gastric chief cell, independent of vascular, paracrine, or neural actions.
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