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Circadian rhythm of pepsin efflux in the fasting rat stomach.

Gastric pepsin efflux, a putative aggressive factor because of its proteolytic activity, was examined to determine if it displays circadian rhythmicity as has been shown for other factors such as acid, bicarbonate, mucus, blood flow, potential difference, and tissue prostacyclin activity. 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 intervals. After anesthesia and minor surgery, the stomach was cannulated and filled with 2 ml of saline for two sequential periods of 30 min. The samples were tested for pepsin according to the modified hemoglobin substrate colorimetric method. The data were analyzed with cosinor rhythmometric techniques. Pepsin efflux displayed significant (p < 0.05) circadian rhythmicity with an acrophase value or peak time at 06:49 h after lights on, during the lights-on resting phase. In contrast, the acrophase for acid secretion in the same model occurs during the dark period, when the rats are normally active. We postulate that differences in the circadian patterns of acid and pepsin may be protective.