The PGE2 level in the rat resting stomach, dropped into liquid nitrogen after removal, was 44.6 +/- 8.3 ng/stomach, when determined by radioimmunoassay, but cutting of the greater curvature with scissors after removal caused an approximately sixfold increase in the PGE2 level. Compression of the stomach in situ with metal tongs refrigerated in liquid nitrogen markedly reduced the PG levels, and further purification by reversed-phase high performance liquid chromatography reduced the PGE2 and 6-keto-PGF1 alpha levels to 4.7 +/- 0.6 and 4.8 +/- 0.8 ng/stomach, respectively. Pretreatment of the rats with indomethacin (10 mg/kg, i.v.) did not decrease the PGE2 level, but the 6-keto-PGF1 alpha level was reduced slightly. The lowest level of PGE2 in the resting state was significantly increased after administration of 1.0 M NaCl solution into the gastric lumen. The peak value was 70.0 +/- 21.8 ng/stomach at 30 min, after which the level decreased gradually. The level of 6-keto-PGF1 alpha was not significantly increased during the administration of 1.0 M NaCl solution.