The present study was designed to investigate the changes in gastric mucosal PGI2 level accompanying the healing of acetic acid-induced gastric ulcers in rats. The ulcers, which were observed with an endoscope, were found to undergo periods of decrease, healing and exacerbation during the rat's lifetime. The phases were categorized as follows: (1) the reduction period (days 3-50 after ulcer induction, corresponding to 7-14 weeks of age), (2) healing period (days 35-150 after ulcer induction, corresponding to 12-29 weeks of age), (3) first exacerbation period (days 35-231 after ulcer induction, corresponding to 12-40 weeks of age), (4) inactive period (days 231-365 after ulcer induction, corresponding to 40-60 weeks of age), and (5) second exacerbation period (days 365-550 after ulcer induction, corresponding to 60-86 weeks of age). In normal rats, the level of gastric mucosal PGI2 gradually increased with aging between 7 and 20 weeks, then decreased up to 40 weeks. The PGI2 level in the 60-week-old rat did not differ from that in the 40-week-old rat. The PGI2 level was the lowest in the 86-week-old rat. In ulcer-bearing rats, the PGI2 level showed the same pattern of change as that in normal rats, but the level was higher. The above results indicated a marked decrease in PGI2 level between 20 and 40 weeks of age and between 60 and 86 weeks of age in normal and ulcer-bearing rats. These periods corresponded closely to the first and second exacerbation periods, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)