Evidence for a role of progesterone in the control of uterine ornithine decarboxylase in the pregnant hamster.

Changes in uterine ornithine decarboxylase (ODC) activity throughout pregnancy and the importance of progesterone in the regulation of this enzyme during the early post-implantation period have been studied in the hamster. Soon after implantation, from day 5 to day 6 of pregnancy, ODC activity rapidly increased. It reached a plateau on day 7, then abruptly fell on day 8 and remained low until the end of pregnancy. DL-alpha-difluoromethyl-ornithine (DFMO), an irreversible inhibitor of ODC, induced pregnancy termination as a consequence of the reduction of uterine ODC activity. When pregnancy arrest was induced by removing endogenous progesterone by administration of prostaglandin F2 alpha (PGF2 alpha) or by ovariectomy, the ODC rise was completely abolished, and exogenous progesterone was able to entirely counteract this effect on the enzyme activity and the termination of pregnancy. These results suggest that progesterone play a significant role in the rise of uterine ODC activity, which appears to be essential for the early post-implantation events needed for pregnancy maintenance.