Hormonal control of ornithine decarboxylase and spermidine/spermine N¹-acetyltransferase activities by sex steroid hormones in the uterus of ovariectomized rats

The weight of the uteri of ovariectomized (OVX) rats was drastically increased by about 5 times at 1 week after one subcutaneous (s.c.) injection of oestradiol, but not changed by hydroxyprogesterone administration. The activities of ornithine decarboxylase (ODC) and spermidine/spermine N¹-acetyltransferase (SAT) in the uterus of OVX rats were controlled by exogenous administrations of the sex steroid hormones, oestradiol and/or hydroxyprogesterone to the OVX rats. ODC activity in the uterus of OVX rats was drastically increased by one s.c. injection of oestrdiol, but not changed by one s.c. injection of hydroxyprogesterone. On the other hand, SAT activity in the uterus of OVX rats was reduced to one-third by oestradiol administration, while by the hydroxyprogesterone administration the enzyme activity was not changed, keeping the control level of SAT activity in the uteri of OVX rats treated with the vehicle (sesame oil). It is noteworthy that the patterns of changes in ODC activity by these hormone treatments are the reverse of the patterns of changes in SAT activity in the uteri of OVX rats. Patterns of ODC activity alteration by these sex hormones were very similar to the patterns of the organ weight alteration, demonstrating that ODC activity correlates to the growth of the organ.