Bile Secretion and Bile Composition in the Freely Moving, Unanaesthetized Rat with a Permanent Biliary Drainage: Influence of Food Intake on Bile Flow

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Abstract
In freely moving, unanesthetized rats bile flow was measured continuously over the whole day-night cycle. Bile composition was analyzed and the influence of food intake on bile flow was investigated. In both sexes a distinct circadian variation of bile production was observed. The mean nighttime production was 50% higher than the daytime value for female rats and 38% higher for male rats. In the morning when the light was switched on, a sharp decrease in secretion rate was evident. Bile flow gradually increased in the afternoon. The pattern of food intake was positively correlated with the pattern of bile secretion. During fasting the mean level of bile flow decreased, but the circadian variation persisted. Refeeding again increased the mean level of bile flow. The chenodeoxycholate/cholate ratio in rats with permanent bile fistulae was higher than in rats with ''acute'' bile fistulae and changed during the day-night cycle. The ratio decreased from 1.01 at 05.00 h to a minimum of 0.41 at 15.00 h. During the day-night cycle the Na, K, Ca and cholesterol concentrations were relatively constant. The total bile salt concentration was only slightly changed. Both the bile salt-dependent fraction and the bile salt-independent fraction were subject to similar circadian variations.