Sex difference in the accumulation of D-beta-aminoisobutyrate in organs of mouse after thymine loading

The concentration of D-beta-aminoisobutyric acid (D-BAIB) in the liver and kidney was twice as high and dropped more slowly in the female mouse than in the male after an intraperitoneal injection of thymine. The concentration of beta-alanine, formed from uracil by the same enzyme system catalyzing formation of D-BAIB from thymine, was not different in the liver and kidney of both sexes after an intraperitoneal injection of uracil. After the intraperitoneal injection of D-BAIB, the concentration of BAIB in male liver decreased faster than that in female liver. Inhibition of D-BAIB: pyruvate aminotransferase caused by injection of D-cycloserine resulted in a significant increase in the concentration of BAIB in liver of both sexes after injection of thymine, but the concentration dropped more rapidly in the male. The activity of D-BAIB: pyruvate aminotransferase was not different in the livers of male and female mice. Under the action of probenecid, an inhibitor of active transport systems, the sex difference in accumulation and disappearance of the amino acid in the liver was not observed. This suggested that the excretion of BAIB is more active in the renal tubules of the male mouse than in those of the female. However, the amount of BAIB excreted in the urine after injection of thymine was larger in the female mice than in the male mice. There may be another probenecid-sensitive enzyme for the disposal of BAIB in male mice.