Concanavalin A binding capacity of preimplation rat embryos

The number of concanavalin A (Con A) binding sites was determined in Days 2–5 rat embryos (Day 1 = sperm‐positive) by Scatchard plot analysis. There were 127 ± 13 million sites on Day 2 (2‐cell), which were decreased slightly to 88 ± 9 million sites on Day 3 (2 ∼ 4‐cell), then increased to 200 ± 24 million sites on Day 5 morning (early blastocyst) and 175 ± 21 million sites on Day 5 evening (late, implanting blastocyst). However, the apparent association constant decreased steadily with development, from about 3 × 10 6 M −1 on Days 2 and 3 to 1.3 × 10 6 M −1 on Day 5 evening. Thus, in comparison with the results of mouse embryos (Wu, '80), the number of Con A binding sites was not increased in the implanting rat blastocyst, as it was in the mouse, although there were comparable numbers of Con A binding sites up to the early blastocyst stage in both species. The data also suggest some changes in the sugar groups, and probably the surrounding groups, on the surface coat of the plasma membrane during the preimplantation stages of development.