Abstract
Phenobarbital decreases the 5'-UMPase activity of the microsomal fraction of rat liver. The rate of decrease and of the return to control values after cessation of phenobarbital treatment reflect the level of liver hypertrophy. Phenobarbital decreases the activity of ribonuclease I (pH 5.6), ribonuclease II (pH 8.0), and ribonuclease III (pH 9.5) in the crude nuclear, mitochondrial, microsomal, and supernatant liver fractions. Decrease commences 2 h after intraperitoneal injection of the drug and continues throughout the chronic treatment. The greatest decrease occurs in the microsomal and supernatant liver fractions. If phenobarbital administration is interrupted after 7 days, then ribonuclease activities of the crude nuclear and mitochondrial fractions attain control values within 2 days, while the return to control values in the microsomal and the supernatant fractions is slower. Phenobarbital in vitro is without effect on either the 5'-UMPase activity of the microsomes or the ribonuclease activity of cellular fractions.
Published Version
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