Abstract
Progesterone level in the peripheral blood plasma of the cow, following intrauterine injec-tion of PGF2α, was investigated.
Cows were injected with either a daily dose of 0.51.0 mg of PGF2α for 2 consecutive days, or with a single dose of 36 mg of PGF2α into the middle portion of uterine horn ipsilateral to the corpus luteum.
In 8 cows treated between Day 2 and Day 4 of the estrous cycle (Day 0=day of ovulation), 4 cows ovulated 814 days after the treatment. The cycle length of the remaining four cows was not changed. Blood level of progesterone following the treatment fluctuated in various patterns; i.e. (A) a pattern that was almost the similar as that found in the normal estrous cycle, (B) concentration of progesterone decreased temporarily after the treatment, then in-creased once again, and was followed by the similar pattern as like as (A), (C) progesterone level showed somewhat to rise temporarily after the treatment, but fell soon, (D) concentration of progesterone decreased temporarily after the treatment and then increased again, but was reduced right soon. Two cows treated for 2 consecutive days at Day 4 and Day 5 of the early luteal stage ovulated 4 days after the treatment. Blood progesterone level fell rapidly after the treatment, and became one-third of the initial level 24 hours after the second treament. Three cows treated singly between Day 9 and Day 11 of the mid luteal stage ovulated 4 days after the treatment. Blood progesterone tended to decrease as early as 3 hours after the treat-ment, and reached up to one-half to one-sixth of the initial levels 24 hours after the treatment. Two cows treated at Day 15 of the late luteal stage ovulated 4 and 6 days after the treatment, respectively. Concentration of progesterone was reduced to one-half in one cow, and in another, less than one-eighth of the initial levels 24 hours after the treatment.
The pattern of the blood progesterone level almost reflected the growing on regressive changes of the corpora lutea examined by rectal palpation.
These results showed that the luteolytic action of the treated PGF2α in cows in the luteal stage, seemed to be very intense at 5 days after ovulation or thereafter, but on the contrary, in very early stage of it up to 4 days after ovulation, the action seemed to be rather weak or indistinct.
