CHANGES IN ORNITHINE DECARBOXYLASE DURING EARLY IMPLANTATION IN THE RAT

Ornithine decarboxylase activity was compared in the right and left horns of unilaterally ovariectomized rats on Days 4 and 5 of pregnancy. It was found that enzyme activity in the pregnant horn was significantly increased over that of the contralateral empty horn by 0400 h on Day 5 before implantation of the blastocyst occurred and reached maximum levels by 0900 h. Similar changes were not observed in the intact horns of uteri from unilaterally ovariectomized rats mated with vasectomized males even though eggs were present. However, intraluminal injection of arachis oil at 1000 h on Day 5 into those horns, a treatment producing massive deciduomas, led to large increases in ODC activity in the treated horn within 5 h. Similar increases were not induced by laparotomy. The data indicates that the decidual response induced by the blastocyst has already commenced by 0400 h on Day 5, in agreement with previous conclusions based on studies of RNA synthesis.