CIRCADIAN-RHYTHMS OF ACID AND BICARBONATE EFFLUX IN FASTING RAT STOMACH

One model of gastric ulcerogenesis implicates a disruption of complementary circadian rhythms between protective and destructive factors. The purpose of this study was to compare circadian rhythms in gastric production of H+ and HCO3- in fasted rats. Sprague-Dawley rats were acclimatized in sound-attenuating, light-proof chambers for 3 wk on a 12:12-h light-dark schedule. Eighteen-hour fasted rats were studied at each of eight sampling times. After anesthesia, the stomachs were cannulated and filled with test solution. Thirty-minute gastric samples were titrated for H+ or assayed for HCO3-. Cosinor analysis of the data showed significant (P < 0.05) circadian rhythms for both H+ and HCO3-. Peak times were 22:45 HALO (hours after lights on) (4:45 A.M.) for H+ and 05:41 HALO (11:41 A.M.) for HCO3-. These data demonstrate that H+ and HCO3- secretion in the fasting rat gastric lumen follow circadian rhythms with different peak times. Theoretically, this may result in circadian rhythmicity of relative mucosal vulnerability to injury.