D-Glucaric acid and gamma-glutamyltransferase as indices of hepatic enzyme induction in pregnancy.

Increased activity of hepatic microsomal enzymes can be evaluated by measuring D-glucaric acid excretion in urine and gamma-glutamyltransferase (EC 2.3.2.2) activity in serum. Aside from diverse foreign compounds, endogenous steroid hormones have been shown to be normal substrates of the microsomal enzyme system. Because there is an increase in steroid production in pregnancy, we sought to determine whether these indices of induction increase during pregnancy. In 90 women in various stages of pregnancy, all with normal kidney function, we measured glucaric acid excretion in urine and activity of the transferase in serum and in urine. Glucaric acid increased markedly during pregnancy, from 14.4 +/- 2.1 in the first trimester to 23.5 +/- 2.8 mumol of D-glucaro-1,4-lactone per gram of creatinine in the third trimester. We saw no correlation between glucaric acid excretion and the transferase activity in serum or urine. Activity of gamma-glutamyl-transferase remains within normal limits throughout pregnancy, which leaves doubt as to the value of this measurement in evaluating enzyme induction owing to endogenous steroids.