Possible antitumor promoter in the glandular stomach: calcium chloride.

Studies were made on the inhibitory effects of CaCl2 and 13-cis-retinoic acid on induction of replicative DNA synthesis (RDS) in the pyloric mucosa of male F344 rats by the glandular stomach tumor promoter, NaCl. RDS in the pyloric mucosa showed a maximum of about a ten-fold increase 17 hr after administration of 3.3 M NaCl and returned to the control level 48 hr after the administration of NaCl. Administration of 400 mM CaCl2 1 hr before NaCl resulted in 60-80% inhibition of the increase in RDS 4-48 hr after NaCl administration. Administration of 20 to 400 mM CaCl2 1 to 2 hr before NaCl caused dose-dependent inhibition of the increase in RDS 17 hr after NaCl administration, with 400 mM CaCl2 causing 80-100% inhibition. Administration of 400 mM CaCl2 1 hr before NaCl also decreased the histological damage of the surface epithelial cells induced by NaCl. Administration of 13-cis-retinoic acid at doses of 10 micrograms-10 mg/kg body weight did not inhibit the increase in RDS in the pyloric mucosa that was induced by NaCl. These results suggest that CaCl2, but not 13-cis-retinoic acid, inhibits tumor promotion in the pyloric mucosa of rat stomach.