Rates of Uteroglobin Synthesis by Endometrial Explants from Different Days of Early Pregnancy in the Rabbit

Uteroglobin is a protein secreted by the rabbit uterus around the time of implantation. To define the mechanism of induction of uteroglobin during pregnancy it is necessary to establish the correlations between transcription of the uteroglobin gene, uteroglobin mRNA level and activity, protein synthesis and secretion, and uteroglobin accumulation in the luminal fluid. This paper reports studies on the cumulative level of luminal uteroglobin and rates of uteroglobin synthesis and secretion by endometrial explants. The rise in cumulative uteroglobin to a plateau of about 22% of secreted protein on Days 4–5 of pregnancy is preceded by an increased rate of uteroglobin synthesis. The protein is not stored in endometrial cells, and newly-synthesized uteroglobin accounts for 60% of the total secreted protein synthesis in explants from Day 4 of pregnancy. There is about a 12-fold rise in the proportional rate of uteroglobin synthesis between Day 0 and Day 4. This rise corresponds to our earlier report of about a 10-fold increase in uteroglobin mRNA activity over the same period. The stimulation of mRNA activity and protein synthesis precedes the increased secretion of uteroglobin and accounts for about half of the cumulative increase in the level of this protein in uterine flushings.