Circadian rhythm of biliary excretion and its control mechanisms in rats with chronic biliary drainage.

Rats with chronic biliary drainage under a rigid lighting schedule (light on at 6 A.M. and off at 6 P.M.) exhibited a remarkable circadian rhythm of bile flow, biliary concentrations and excretory rates of bile salts, cholesterol, and phospholipid. The peak was attained at midnight and nadir at noon except for the peak concentrations of cholesterol and phospholipid occurring at 8 P.M. Cholesterol feeding abolished the circadian rhythm of biliary cholesterol and phospholipid concentrations but not their excretory rates because the daily fluctuation of the bile flow remained unchanged. Bilateral vagotomy enhanced the bile flow rate and shifted the peak of circadian rhythm of all parameters except bile salt 4 h earlier. Bilateral adrenalectomy abolished the circadian variation of the concentration of cholesterol and phospholipid and minimized that of bile salt, but the daily fluctuation of their excretory rates persisted in a lower amplitude. The studies suggested that such circadian rhythm might be controlled simultaneously by multiple factors and could not be entirely abolished by any single special treatment.