Studies on inhibition of nucleic acid biosynthesis by isoniazid and its possible prevention.

Effect of isoniazid on nucleic acid biosynthesis was studied in Swiss mice. It was observed that i.p. injection of isoniazid stimulated activities of nuclease. Isoniazid also inhibits RNA biosynthesis in lung and liver tissue of 3-weeks old mice but has no inhibitory effect on the same in 6 weeks old mice. It inhibits DNA biosynthesis in lung tissue of 3- and 6-week old mice. With the decrease in nucleic acid biosynthesis and increased activities of nucleases the nucleotide pool is increased. I.p. injection of ammonium chloride produces inhibition of nucleic acid biosynthesis to a similar extent. Administration of amino acids L-arginine or L-Na-glutamate or of vitamins pyridoxine or folic acid along with isoniazid prevents the inhibitory effect of isoniazid on nucleic acid biosynthesis.