Hormonal regulation of ornithine decarboxylase and polyamines in primary cultured rat hepatocytes. Differences in hormonal response between adult and fetal hepatocytes

Polyamines are polycationic substances which are widely distributed in living organisms and have a close relation to rapid growth phenomena. We examined ornithine decarboxylase (ODC), which is the rate limiting enzyme of polyamine biosynthesis, and polyamine induction in primary cultured rat hepatocytes by various hormones which increase during pregnancy, and revealed differences in hormonal responses between adult and fetal rat hepatocytes. Thirteen hormones, including estrone, estradiol, progesterone, testosterone, human chorionic gonadotropin (HCG), cortisol, dexamethasone, insulin, glucagon, epinephrine and epidermal growth factor (EGF), were tested. Among these hormones, only insulin, dexamethasone and EGF induced ODC activity and polyamine biosynthesis, especially that of putrescine, in both adult and fetal hepatocytes. The effects of EGF were the most significant. The combined effect of insulin and dexamethasone was additive, while that of insulin and EGF was synergistic. The rate of ODC induction was higher in adult hepatocytes than in fetal hepatocytes; however, the reaction was earlier in fetal hepatocytes. These observations suggest that ODC and polyamines in the fetal stage of development are regulated by a mechanism different from that in the adult liver.