Relationship between ornithine decarboxylase activity and gastric damage.

Hypertonic NaCl increases the activity of gastric mucosal ornithine decarboxylase (ODC). Intragastric administration of concentrated NaCl solution also induces ulcers in the glandular gastric mucosa. The relationship between ODC activity and gastric mucosal damage and the significance of ODC increases in hypertonic NaCl-treated rats are unknown. Rats were fasted 24 h before being given 1.0 ml of 3.4 M NaCl, 120 mM aspirin in 100 mM HCl or 50% ethanol intragastrically. The oxyntic gland mucosa was removed and assayed for ODC and in some experiments DNA, RNA, and protein content. DNA, RNA, and protein content were decreased by 3.4 M NaCl, and these decreases were much greater if ODC was inhibited by pretreatment with alpha-difluoromethylornithine (DFMO). Both aspirin and 3.4 M NaCl induced ODC activity 6 h later. However, DFMO increased the lesion index only in NaCl-treated rats. Although ethanol produced damage, it had no effect on ODC levels, and DFMO did not alter the severity of ethanol lesions. When different concentrations (0.4, 0.8, 1.6, 2.5, and 3.4 M) of NaCl were administered, ODC activities were increased 6 h later in rats receiving 1.6, 2.5, and 3.4 M NaCl but not lower concentrations. Gross lesions appeared in response to the 2.5 M dose and increased with increasing NaCl concentration. However, microscopic damage of the gastric mucosa occurred at all the concentrations tested. These data show that 1) ODC activation is not necessarily produced by damage, 2) in the case of NaCl, increasing damage increases ODC, and 3) ODC appears to have a role in the prevention of a recovery to damage caused by NaCl.