SEQUENTIAL EVALUATION OF GASTRIC INTRALUMINAL PROSTAGLANDIN-E2 RELEASE, ACID-SECRETION AND DNA-FLOW CYTOMETRY IN N-METHYL-N-NITRO-N-NITROSOGUANIDINE GASTRIC CARCINOGENESIS IN THE RAT

The study was initiated to evaluate the sequential changes of gastric intraluminal prostaglandin E2 (PGE2), gastric acid secretion and of the DNA-flowcytometric patterns during gastric carcinogenesis induced by 45-week N-methyl-N-nitro-N-nitrosoguanidine (NG) administration in the rat. Twenty male chronic gastric fistula Sprague-Dawley rats received NG solution (120 mg/l) for 45 weeks and 20 were used as controls. Samples of gastric juice (1 h) were obtained from all animals under basal conditions and every 5 weeks until the end of the experiment. Aliquots of gastric juice were titrated with 0.1 N NaOH. Other aliquots were extracted with ethylacetate and processed for specific PGE2 RIA. On the day following gastric juice collection a gastric lavage and gastric biopsies (n = 4) were obtained through the fistula and processed for flowcytometry. All surviving animals were killed after 45 weeks and histology was obtained. The incidence of cancer in NG treated chronic gastric fistula rats was 66%. Flowcytometry segregated at an early stage (30-35 weeks) those animals which were to develop gastric carcinoma from those which were not. Administration of NG decreased gastric secretion volume, acid and intraluminal PGE2 concentration both in animals developing and not devloping cancer. During the last 10 weeks a sharp rise in gastric intraluminal PGE2 concentration was observed in tumor-bearing animals only probably due to production by tumor cells. Prostaglandin deficiency may contribute to the NG-induced mucosal damage and may be involved in gastric carcinogenesis.