Phenobarbital Influences the Development of Sodium Retention in Liver Disease Induced by Bile Duct Ligation in the Rat

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Abstract
The onset of sodium retention in phenobarbital/carbon tetrachloride–induced cirrhosis in rats is preceded by a linear decrease in hepatic function as assessed by the aminopyrine rate constant of elimination. Sodium retention occurs when liver function decreases below a critical aminopyrine rate constant of elimination threshold of 1 min- × 10-3. The objective of this study was to investigate this relationship in a different experimental model of cirrhosis in rats and to learn whether alteration of drug–metabolizing activity by hepatic enzyme induction changes the threshold for urinary sodium retention. Cirrhosis was induced in untreated and phenobarbital–treated rats by bile duct excision. Liver function, assessed by the aminopyrine breath test, and urinary sodium excretion on a constant salt diet were measured weekly for up to 4 wk. In untreated rats, the aminopyrine breath test rate constant of elimination was reduced by about 40% within 1 wk of surgery. Aminopyrine rate constant of elimination then decreased more slowly, but linearly. Urinary sodium excretion was initially unchanged, but sodium retention occurred after 2.5 wk and was maintained until the end of the experiment. Phenobarbitaltreated rats had greater initial aminopyrine rate constant of elimination, but we saw a similar fall in aminopyrine rate constant of elimination of about 40% within 1 wk of bile duct excision to a value still above baseline aminopyrine rate constant of elimination of untreated controls. Aminopyrine rate constant of elimination remained at a plateau for 3.5 wk without changes in urinary sodium excretion. After 3.5 wk, a sudden decrease in aminopyrine rate constant of elimination was associated with the sudden onset of sodium retention. Aminopyrine rate constant of elimination was 1.2 min-1 × 10-2 in both groups when sodium retention occurred. There was no change in serum sodium, serum creatinine or creatinine clearance after sodium retention. These results suggest that the threshold of liver function below which sodium retention occurs is independent of the experimental model of cirrhosis. The observation that phenobarbital induction does not alter the threshold, despite increasing the metabolism of aminopyrine, and that it delays the onset of sodium retention indicates that induction with this drug also influences the hepatic determinant of renal function to a similar extent as oxidative metabolism.(HEPATOLOGY 1990; 11:773–778.)

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