The Glycocalyx of the Mouse Uterine Luminal Epithelium during Estrus, Early Pregnancy, the Peri-Implantation Period,and Delayed Implantation. I. Acquisition of Ricinus communis Binding Sites during Pregnancy 1

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Abstract
Mouse uteri were examined during estrus, early pregnancy, the peri-implantation period and delayed implantation to determine whether changes in the surface coat of the luminal epithelium could be associated with receptivity of the uterus to the presence of blastocyst-stage embryos or blastocyst adhesion. By using alkaline bismuth subnitrate to label periodate-oxidized glycols within the glycocalyx the authors were able to measure the thickness and examine the morphology of the glycocalyx by EM. Ferritin-conjugated R. communis agglutinin (RCA-I) demonstrated the presence of D-galactose at terminal, nonreducing positions within the glycocalyx. A relatively thick (0.06-0.1 .mu.m) surface coat was present during estrus, but contained almost no RCA-I binding sites. During day 3 of pregnancy the surface coat remained up to 0.1 .mu.m thick and RCA-I binding sites were present. At day 4 and during delay the glycocalyx had a fibrillar appearance, contained RCA-I binding sites and was reduced to 0.06-0.08 .mu.m in thickness. During day 5 of pregnancy the thickness of the surface coat was greatly reduced, but there remained uniform lectin binding adjacent to the plasma membrane both at sites of blastocyst attachment and between implantation sites. The luminal epithelium of the mouse uterus evidently acquired RCA-I binding sites during pregnancy; the thickness of the surface coat was greatly reduced at the time of implantation.
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