Ornithine decarboxylase activity in human fetal liver

In human fetal liver ornithine decarboxylase (EC. 4.1.1.17 (ODC)) was found to have a K_m of 3.3 × 10^-4 M. During human fetal development, hepatic ODC activity declined from a peak of 379 pmol/60 min/mg protein in the youngest tissue examined (5.2 cm crown-rump length, 10 weeks of gestation) to values of 1.3 ± 0.2 in fetuses greater than 12 cm (14 15 weeks of gestation). Explants of human fetal liver maintained in organ culture for 32 hr demonstrated no ODC activity in the presence or absence of insulin (1 U/ml). Explants of rat fetal liver achieved a steady state of ODC activity (12% of the fresh tissue activity) after 16 hr in organ culture and maintained this for an additional 14 hr. Regulation of hepatic ODC activity in the developing human fetus may result from hormonal influences, particularly human growth hormone (HGH) and very possibly human chorionic somatomamotropin (HCS).