Investigation of Estetrol during fetal development period of rats

The majority of published studies on Estetrol (E4) indicate that E4 is a hormone synthesized in humans and, to a limited extent, in some higher mammals and is not found in rodents such as rats and mice. However, the number of studies specifically investigating the presence of E4 in other species is limited. Studies investigating its presence in rodents were not found by us. The demonstration that a molecule known to be secreted in the human fetus is not produced in the rat fetus will make a great contribution to the understanding of why E4 is secreted and what its function is by emphasizing the different developing tissues of these two species during fetal development. Demonstrating that it is present in the rat fetus would also contribute greatly to the understanding of why E4 is secreted and what its function is, with emphasis on the similar developing tissues of the two species. The primary aim of the study was to test the presence of E4 in the rat embryo and fetus. Our working hypothesis was 'E4 is a hormone synthesized during rat pregnancy'. For this purpose, embryo and fetus samples of pregnant Sprague-Dawley rats from the 2nd gestational day (EG2) to the 21st gestational day (EG21) were removed without contamination and E4 and estradiol (E2) levels were determined from these samples by high performance liquid chromatography (HPLC) method. In our HPLC study, the retention time of E4 on the column was 3.023 minutes for 262nm wavelength. The retention time of E2 in the column was 4.542 for 262nm wavelength. In our study, E4 was detected by HPLC method in embryo and fetus samples as of the 8th day of rat pregnancy. It was not detected in the non-pregnant rat and in the first 7 days of the rat embryo. E2 was detected by HPLC in all embryo and fetus samples, as well as in the uterus of non-pregnant female rats. The observation of E4 by EG8 suggests that E4 secretion in the rat begins with the completion of the blastocyte implantation process. E4 was detected in brain tissue every day from EG14 (EG14 to EG21). In liver tissue, it was detected only at EG20 between EG17 and EG21. In contrast, E4 was detected in the placenta of EG15, EG16, EG17 and EG18. E4 synthesis in the rat may occur in the placenta. In our study, to test that the peak area selected for E4 was the correct peak area, E4 internal standard was added to 4 randomly selected samples; EG21 brain, EG20 liver, EG3 and EG5. First, the vials of these samples without added internal standard and then the vials with added internal standard were analyzed in the HPLC system separately. The chromatograms of the samples with and without added internal standard were compared by subtracting the peak areas from each other. As a result, it was concluded that the peak area selected for E4 was the correct peak area. By demonstrating the presence of E4 in the rat, our study is the first to show that E4 is not a hormone specific to humans and some higher mammals. E4 is secreted in rat pregnancy similar to human pregnancy. In the rat, E4 may be produced specifically for one or all of the following processes: placental-fetal circulation, central nervous system development and bone development. Given that we detected the presence of E4 in brain tissues on all days from EG14 onwards, E4 may be involved in the cerebral cortex, particularly in the migration of neuroblasts. Further studies with human and rat fetal tissues will contribute to the understanding of the role of E4. EGE UNIVERSITYOffice of Scientific Research Projects Project confirmation number: 29714 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.