Haptoglobin expression and release by rabbit oviduct and endometrium, its localization in blastocyst extra-embryonic matrix and fluid during preimplantation time

BACKGROUND: Evidence is emerging that haptoglobin, an acutephase protein with immunomodulatory properties, is expressedby the endometrium of various species. The present study describesan in-depth investigation of haptoglobin expression and releasein the rabbit reproductive tract and in preimplantation embryos.METHODS: The full-length cDNA sequence of rabbit haptoglobinwas determined by rapid amplification of cDNA ends PCR. Haptoglobinexpression was studied in the oviductal ampull, and isthmus,endometrium and embryos from the time of ovulation up to adhesion.These results were completed by western blot analysis of reproductivetract secretions and embryonic tissues. RESULTS: cDNA sequencingshowed a high homology between rabbit and human haptoglobin(84.1%). In oviductal tissues haptoglobin mRNA is clearly expressedfrom 6 h post-conception (p.c.) to day 3, and in the uteruson days 5 and 6. In the oviductal fluid highest haptoglobinprotein content was found between 6 h p.c and day 2, and inthe uterine fluid on days 5 and 6 p.c. Embryos do not expresshaptoglobin mRNA during preimplantation development. However,considerable amounts of maternal haptoglobin protein were detectedin the blastocyst coverings and in blastocyst fluid. CONCLUSIONS:Already during periovulatory time and oviductal passage, highamounts of haptoglobin are present in the microenvironment surroundingthe oocyte/embryo. Two days before implantation, again, highhaptoglobin levels are detectable in the embryo's environment.The incorporation of haptoglobin into the extra-embryonic matrixmay be of particular functional significance.