Changes in Uterine Sialic Acid and Glycogen During Early Pregnancy in the Rat

Abstract

Changes in uterine sialic acid and glycogen were studied in rats during days 1–6 of pregnancy. There was a sharp decline in uterine glycogen following mating, and thereafter increased gradually to reach a peak level on day 4 (4 PM). Coinciding with the entry of blastocysts into the uterus [between day 4 (10 PM) and day 5 (10 AM)] uterine glycogen decreased to a low level which was maintained up to 4 PM on day 6 of pregnancy. Uterine sialic acid was maximal on day 0 (proestrus, 10 PM) and was maintained at this level up to day 1 of pregnancy. Thereafter, uterine sialic acid concentration declined gradually to the lowest level by day 4 (9 AM). There was a sharp increase in uterine sialic acid between 4 and 10 PM On day 4, and was followed by a marked decline between day 4 (10 PM) and day 5 (9 AM); it increased again on the evening of day 5 and attained significantly higher levels by day 6 (4 PM). The fluctuations in uterine sialic acid and glycogen during early pregnancy appear to be a sequel to the fluctuating levels of estrogens during proestrus, estrus, and early pregnancy. A possible role for sialic acid in attachment of blastocysts to the uterus is postulated.