Histological effect of (R)-alpha-methylhistamine on ethanol damage in rat gastric mucosa: influence on mucus production.

(R)-alpha-Methylhistamine, a selective agonist of histamine H3 receptors, prevents macroscopically visible gastric lesions by absolute ethanol in the rat. A further insight into its activity was the aim of our study. Rats were given saline or (R)-alpha-methylhistamine (100 mg/kg) intragastrically. After 30 min, absolute ethanol was given and gastric mucosa was sampled 60 min later. Histologic damage and intracellular and adherent mucus were quantified. Luminal surface and mucous cells were examined by scanning and transmission electron microscopy. (R)-alpha-Methylhistamine reduced the extent of lesions by ethanol from 96 to 18%. Surface mucous cells and mucous neck cells were increased in volume and number, packaging of intracellular mucus was modified, and the secretory processes were promoted by (R)-alpha-methylhistamine itself, although these modifications were mostly evident in stomachs subsequently exposed to ethanol. Adherent mucus layer thickness was increased by (R)-alpha-methylhistamine only after ethanol exposure. It is concluded that (R)-alpha-methylhistamine predisposes mucous cells to react to ethanol.