Interactions between sialoadenectomy and capsaicin-sensitive afferent fibers on gastric acid secretion in rats

Capsaicin and gastric ulcers

In recent years, infection of the stomach with the organism Helicobacter Pylori has been found to be the main cause of gastric ulcers, one of the common ailments afflicting humans. Excessive acid secretion in the stomach, reduction in gastric mucosal blood flow, constant intake of non-steroid anti-inflammatory drugs (NSAIDS), ethanol, smoking, stress etc. are also considered responsible for ulcer formation. The prevalent notion among sections of population in this country and perhaps in others is that "red pepper" popularly known as "Chilli," a common spice consumed in excessive amounts leads to "gastric ulcers" in view of its irritant and likely acid secreting nature. Persons with ulcers are advised either to limit or avoid its use. However, investigations carried out in recent years have revealed that chilli or its active principle "capsaicin" is not the cause for ulcer formation but a "benefactor." Capsaicin does not stimulate but inhibits acid secretion, stimulates alkali, mucus secretions and particularly gastric mucosal blood flow which help in prevention and healing of ulcers. Capsaicin acts by stimulating afferent neurons in the stomach and signals for protection against injury causing agents. Epidemiologic surveys in Singapore have shown that gastric ulcers are three times more common in the "Chinese" than among Malaysians and Indians who are in the habit of consuming more chillis. Ulcers are common among people who are in the habit of taking NSAIDS and are infected with the organism "Helicobacter Pylori," responsible for excessive acid secretion and erosion of the mucosal layer. Eradication of the bacteria by antibiotic treatment and avoiding the NSAIDS eliminates ulcers and restores normal acid secretion.

Different effect of antiulcer agents on rat cysteamine-induced duodenal ulcer after sialoadenectomy, but not gastrectomy

The focus was on salivary glands in cysteamine-induced duodenal ulcer and the different effects of antiulcer agents on cysteamine-induced duodenal ulcer in sialoadenectomized but not gastrectomized rats. We tested antiulcer agents on cysteamine-induced duodenal ulcer in rats (agents/kg i.p.) simultaneously with cysteamine 400 mg/kg s.c., rat killed 24 h thereafter subjected to no surgery (normal), to gastrectomy (24 h before) or sialoadenectomy, acute (24 h before) or chronic (21 days before). (i) Ulcerogenesis: cysteamine-induced duodenal ulcer had the same severity and incidence in normal, gastrectomized or acutely or chronically sialoadenectomized rats. (ii) Antiulcer effect under normal conditions or following gastrectomy: in normal or gastrectomized rats all agents tested, gastric pentadecapeptide BPC 157 [currently in clinical trials for inflammatory bowel disease (PL-10, PLD-116, PL-14736, Pliva) (10.0 microg or 10.0 ng), ranitidine (10 mg), atropine (10 mg), omeprazole (10 mg)] inhibited cysteamine-induced duodenal ulcers, acting through gastric acid-independent mechanisms. Following sialoadenectomy, acute or chronic: ranitidine, omeprazole and atropine were completely ineffective, while pentadecapeptide BPC 157 could protect. Thus, we found that contrary to stomach, salivary glands are implicated in cytoprotective agent activity (standard agents were ineffective after sialoadenectomy). Also, gastric pentadecapeptide BPC 157 was consistently associated with a cytoprotective effect, suggesting a beneficial activity distinctive from that of H2-receptor blockers, proton-pump inhibitors and anticholinergics; but probably replacing missing salivary glands factors.

Importance of nitric oxide and capsaicin-sensitive afferent nerves in healing of stress lesions induced by epidermal growth factor

Epidermal growth factor (EGF) is a potent mitogen implicated in gastroprotection and ulcer healing, but its possible interaction with nitric oxide (NO) and sensory nerves on healing after acute gastric damage has not been assessed. We examined the effects of topical application of a small dose (0.5 mg/kg) of capsaicin to stimulate sensory nerves and a larger parenteral dose of capsaicin (125 mg/kg s.c.) to deactivate these neurons or the effect of systemic administration of NG-nitro-L-arginine methyl ester (L-NAME) (20 mg/kg i.v.) to suppress NO synthase on healing of gastric lesions induced by 3.5 h of water immersion and restraint stress (WRS) in rats without or with EGF administration. Rats were sacrificed at 0, 6, 12, or 24 h after WRS and the gastric blood flow (GBF) was measured by the H2 gas clearance technique. Exposure to WRS produced many gastric lesions, with a marked decrease in GBF, but at 12 h these lesions started to heal and the lesion number was reduced by 75% after 24 h. This was accompanied by progressive increase in the GBF and an increase in expression of EGF mRNA in gastric mucosa, as detected by RT-PCR. Pretreatment with L-NAME or functional ablation of sensory nerves by capsaicin significantly delayed the healing of WRS lesions and accompanying hyperemia. In contrast, pretreatment with EGF (100 micrograms/kg s.c.) or glyceryl trinitrate (10 mg/kg i.g.), a donor of NO, or stimulation of sensory nerves by topical capsaicin significantly enhanced the healing of these lesions and increased the GBF. The acceleration of the healing and accompanying hyperemia induced by EGF at 12 h after WRS were completely reversed in rats pretreated with L-NAME or in those with capsaicin denervation. Addition of L-arginine but not D-arginine to L-NAME restored the healing of stress lesions and gastric hyperemia induced by this peptide. Removal of salivary glands, which reduced luminal content of EGF and DNA synthesis by about fourfold compared to rats with intact glands, produced a significant delay in healing, and this was further aggravated by capsaicin denervation. We conclude that EGF, sensory nerves, and NO play an important role in the healing of gastric mucosa from lesions induced by stress and that sensory nerves and NO appear to interact with EGF in the mechanism of mucosal recovery from stress lesions.

Effect of epidermal growth factor, transforming growth factor alpha and nerve growth factor on gastric mucosal integrity and microcirculation in the rat

In the present study we have compared the effects of the peptide growth factors epidermal growth factor (EGF), transforming growth factor alpha (TGF alpha) and nerve growth factor (NGF) on gastric mucosal integrity and mucosal blood flow in the rat. Mucosal damage was assessed 30 min after intraluminal instillation of 40% (w/v) ethanol (EtOH). EtOH treatment resulted in an increase in mucosal damage when compared to saline treated control animals. Administration of each growth factor either by tail vein (i.v.; 0.2-1 nmol/kg) or via the left gastric artery (i.a.; 0.05-0.2 nmol/kg) resulted in a significant reduction in the extent of mucosal damage. The growth factors reduced EtOH-mediated damage in an equipotent manner. The reduction in the area hemorrhagic damage ranged from -25 to -35% from EtOH alone when the factors were administered i.a. and from -75 to -85% when delivered i.v. Gastric mucosal blood flow as assessed by laser Doppler flowmetry (LDF) was increased in a dose-dependent and equipotent manner by EGF and TGF alpha administered either by the i.v. or i.a. route. LDF changes were greater when EGF or TGF alpha were delivered via the i.a. route. NGF did not significantly increase blood flow regardless of the dose or route of delivery. beta-Adrenoceptor blockade with propranolol (0.75 mg/kg i.v.) abolished the increase in LDF in response to EGF or TGF alpha but did not affect the ability of these growth factors to reduce EtOH-mediated damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of nitric oxide and salivary gland epidermal growth factor in the modulation of rat gastric mucosal integrity

1. The interaction between endogenous nitric oxide (NO) and factors from the rat submandibular salivary gland such as epidermal growth factor (EGF) on gastric mucosal integrity in the rat has been investigated. 2. Bolus administration of the NO synthase inhibitor, NG nitro-L-arginine methyl ester (L-NAME; 6.25-50 mg kg-1, i.v.) to animals treated intraluminally with 0.15 N HCl resulted in a significant increase in the area of mucosal haemorrhagic damage at doses 12.5 and 50 mg kg-1. Concurrent administration of indomethacin (5 mg kg-1, i.v.) resulted in a significant haemorrhagic mucosal damage in response to L-NAME (12.5-50 mg kg-1). Administration of the highest dose of L-NAME resulted in an increase in histological damage to the rat gastric mucosa. 3. When compared to control animals, the extent of damage produced by L-NAME or L-NAME in combination with indomethacin was significantly exacerbated in rats which had been sialoadenectomized (SALX) by removal of the submandibular salivary glands. The mucosal damage in SALX rats was ameliorated by treatment with EGF (5 and 10 micrograms kg-1, i.v.). 4. L-NAME administration resulted in a small reduction of gastric mucosal blood flow as assessed by laser Doppler flowmetry (LDF). The reduction in LDF by 25 and 50 mg kg-1 L-NAME was significantly greater in SALX rats than in rats with intact salivary glands. Pretreatment of SALX rats with indomethacin did not augment this large decrease in LDF suggesting that endogenous prostanoids do not interact with NO and salivary factors in regulating mucosal microcirculation. 5. Mucosal NO biosynthesis as assessed by ['4C]-citrulline formation was reduced in SALX rats when compared to control animals. Pretreatment of SALX animals with parenterally-administered EGF(10 microg kg-1) was associated with an increase in [14C]-citrulline formation in the gastric mucosa to levels observed in control SALX rats.6. These data suggest that factors which originate from the salivary gland such as EGF interact with NO in the maintenance of mucosal integrity. The effects may be mediated at least in part by changes in gastric mucosal blood flow. Salivary glands and EGF may mediate these effects to some extent via changes in mucosal NO biosynthesis.