Abstract
An experimental investigation was made in cows to explore the time, when the action of luteoly-tic factor would be manifested, as a result of the induced inflamation on the endometrium. After injecting with iodine solution into the uterus of each cow in different estrous cycle, peripheral plasma progesterone, estrous cycle length, and corpus luteum were examined.
After the treatment with iodine infusion, the estrous cycle length of the four cows treated at Day 3 of the cycle (Day 0=day of ovulation) was reduced to 912 days. The concentration of plasma progesterone increased for 23 days following the treatment, but decreased rapidly at 34 days after treatment and became very low at the time of estrus. On the contrary, the cycle length was not changed in a cow treated at Day 11. Progesterone level in this cow exhibited a maximum value on the following day of the treatment, remained at this state for 8 subsequent days, then decreased rapidly at the proestrus. This pattern and also the level of the plasma progesterone were not essentially different from those observed in the normal estrous cycle of this cow. The length of estrous cycle in two cows, that were treated at either Day 17 or 18 was prolonged to 29 and 27 days, respec-tively. In these two cases, the plasma progesterone suddenly began to rise on the following day of the treatment and reached the highest peak of the cycle induced, at 3-5 days after the treatment (at Day 2022) and then the level fell down thereafter. The pattern of plasma progesterone con-centration almost reflected the growing or regressive changes of corpora lutea in these cows, which were examined by rectal palpations.
These results obtained seemingly indicated that the luteolytic factor which was produced by the effect of the inflamation in the endometrium began to realize its action at 34 days after inducing the inflamation in cows of the early luteal phase, and in cows of the late luteal phase, this appeared a little later, or at 56 days after inducing inflamation. Besides, it was quite suggestive that the luteal function seemed to be activated temporarily in cows of the late luteal phase, when the infla-mation was induced in the endometrium.
