An update on histamine receptors and the gastrointestinal tract

Effect of a Histamine H2Type Receptor Antagonist (WY 45, 727) on the Healing of Gastric Ulcers in Ponies

Using video gastroscopy, the efficacy of a Histamine-H2 type receptor antagonist (WY 45, 727) was investigated in young ponies with spontaneous and experimentally induced gastric ulcers. Oral administration of WY 45, 727 at 2 mg/kg and 10 mg/kg of body weight every 12 hours for 14 days resulted in complete healing of spontaneous gastric ulcers in the non-glandular portion of the stomach in 2/5 (40%) and 3/4 (75%) of the ponies, respectively, compared (P < 0.05) to 0/5 (0%) placebo-treated ponies. After intramuscular administration of flunixin meglumine at 1.5 mg/kg body weight every 8 hours for 6 days, 9/18 ponies had ulcers in the non-glandular portion of the stomach. Oral administration of WY 45, 727 at 10 mg/kg body weight every 12 hours for 14 days resulted in complete healing of the non-glandular gastric ulcers in 3/4 (75%) compared with (P < 0.05) 1/5 (20%) placebo-treated ponies. This study indicates that 1) the occurrence of subclinical ulcers may be common in young ponies; 2) flunixin meglumine at 1.5 mg/kg intramuscularly every 8 hours for 6 days may result in ulcers of the non-glandular stomach in ponies; and 3) WY 45, 727, a histaminergic H2 type receptor antagonist could be of value in the therapeutic management of ulcers in the non-glandular stomach of foals and adult horses.

Comparison of methods for intestinal histamine application: histamine in enterosoluble capsules or via a duodeno-jenunal tube. Influence of fast and histamine-restrictive diet

The study was conducted to investigate whether introduction of histamine in enterosoluble capsules produced the same amount of urinary histamine metabolites as that found after application of histamine through a duodeno-jejunal tube. Secondly, to examine whether a histamine-restrictive or a fast diet affected the amount of urinary metabolites. Fifteen healthy subjects were challenged four times with 100 mg of histamine. Results were monitored by the urinary recovery of 1,4-methylimidazole acetic acid (MIAA) from 24 h before to 72 h after challenge. Urine was collected in 24-h samples except on the first day after challenge when separation into 0-2h-, 2-4 h- and 4-24 h-fractions was made. MIAA was measured by high performance liquid chromatography (HPLC). The results showed that during the first 2 h after challenge the recovery of MIAA was higher with tubes than with capsules. Measurements from all other intervals did not differ significantly between the two challenge regimens. Fast (water only) and histamine-restrictive diet versus non-restrictive diet did not affect the urinary MIAA. MIAA was significantly higher overall during the first 24 h after challenge than in any other fraction. We conclude that oral administration of enterosoluble capsules is an easy and appropriate method for intestinal histamine challenge. Fast and histamine-restrictive diets are not necessary, but subjects should record unexpected responses in a food and symptom diary.

Histamine content, diamine oxydase and histidine decarboxylase activities along the intestinal tract of the rat

Histamine is widely distributed in the intestine where it is involved in many pathological reactions. The relations between histamine content, diamine oxidase and histidine decarboxylase activity have been investigated along rat's intestine. Results showed significant variations along the intestine. A correlation was observed between histamine and histidine decarboxylase (p less than 0.01), both of them being even in the small intestine (11.8 +/- 2.3 ng/mg ww and 112.5 +/- 21.2 fmoles/hr/mg ww respectively), significantly higher in the caecum (16.3 +/- 1.9 and 178 +/- 20.1) and significantly smaller in the colon (7.3 +/- 1.1 and 65.3 +/- 11.5) than in other intestinal segments. Diamine oxydase activity was higher in ileum (30.7 +/- 7.2 pmoles/min/mg ww) than in jejunum (17.1 +/- 2.8), caecum (4.3 +/- 0.8) and colon (2.6 +/- 2.7), and could not be linked to histamine content. The results fitted in the hypothesis that histamine in rat intestine is mainly located in mast cells where HDC is probably the main enzyme involved in its modulation.

Clinical pharmacology of the gastrointestinal tract

This article discusses the various drugs that affect the equine gastrointestinal tract. Drugs that alter intestinal motility, that protect the gastrointestinal tract, and that alter secretions, as well as analgesics, appetite stimulants, and orally administered antimicrobial agents are reviewed.