CIRCADIAN-RHYTHM OF PEPSIN EFFLUX IN THE FASTING RAT STOMACH

Gastric pepsin efflux, a putative aggressive factor because of its pro teolytic activity, was examined to determine if it displays circadian rhythmicity as has been shown for other factors such as acid, bicarbon ate, mucus, blood now, potential difference, and tissue prostacyclin a ctivity. Ninety-six fasted Sprague-Dawley male rats, 6-7 weeks of age were acclimated in sound-attenuating, light-proof chambers on a 12/12 light/dark schedule. They were studied in groups of 12 at 3-h interval s. After anesthesia and minor surgery, the stomach was cannulated and filled with 2 ml of saline for two sequential periods of 30 min. The s amples were tested for pepsin according to the modified hemoglobin sub strate colorimetric method. The data were analyzed with cosinor rhythm ometric techniques. Pepsin efflux displayed significant (p < 0.05) cir cadian rhythmicity with an acrophase value or peak time at 06:49 h aft er lights on, during the lights-on resting phase. In contrast, the acr ophase for acid secretion in the same model occurs during the dark per iod, when the rats are normally active. We postulate that differences in the circadian patterns of acid and pepsin may be protective.