ovulation. At this time (late diestrus) oxytocin receptors are up-regulated on the
endometrium of the uterus and luteolytic mechanisms are initiated. Oxytocin produced
by the luteal cells bind to receptors in the uterus and cause production of prostaglandin F2
alpha (PGFatt). Prostaglandin travels to the ovary and causes regression of the corpus
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6
luteum. Regression of the corpus luteum, results in the animal entering the follicular
phase and preparing for estrus.
However, luteolysis can be blocked if a growing conceptus is present in the
uterus. The period around the time of luteolysis is critical for maternal recognition of
pregnancy. The early conceptus releases bovine interferon tau (blFN-x), an antiluteolytic
signal, which blocks production of PGFaa and therefore regression of the corpus luteum.
Inability of the conceptus to adequately communicate with the uterine endometrium
accounts for over 40% of early embryonic losses (Thatcher et al., 1994; from Thatcher et
al., 2001b).
Follicular Dynamics