Glycoconjugate synthesis during early pregnancy: hyaluronate synthesis and function.

The synthesis of various glycoconjugate classes by mouse uteri during the pre- and peri-implantation period has been examined using [3H]glucosamine as a metabolic precursor. A unique and dramatic (five- to sixfold) increase was observed in the synthesis of hyaluronate on the day upon which embryo implantation normally occurs. Mated, but nonpregnant mice did not display increased hyaluronate biosynthesis. In contrast to hyaluronate, the synthesis of most other types of glycoconjugates remained fairly constant during the first 5 days of pregnancy. Low (1500-5000)-molecular-weight N-linked oligosaccharides constituted the major class of oligosaccharides synthesized under all conditions. High (greater than 10,000)-molecular-weight glycoconjugates constituted the second most abundant class of glycoconjugates synthesized (20-30%). Most (85%) of the newly synthesized hyaluronate was associated with the nonepithelial cell types of the uterus. Experiments using ovariectomized mice receiving steroid hormones demonstrated that uterine hyaluronate synthesis was induced preferentially by an artificial decidual stimulus and implicated stromal cells as the site of hyaluronate synthesis. In addition, it was demonstrated that tissue culture plates coated with hyaluronate, but not other polysaccharides, support attachment and spreading of a large fraction (60 to 70%) of embryos cultured in serum-free medium. Collectively, these studies indicate that increased hyaluronate biosynthesis accompanies decidual responses in the endometrium and may promote embryo implantation following initial penetration of the uterine epithelium.