Two experiments using twenty-four sows and forty-eight gilts were designed to study ovarian and pituitary functions after treatment with oestradiol-17β (3 mg/day), progesterone (150 mg/day) or ICI 33828 (50 or 100 mg/day). The dose levels were chosen so that oestrus and ovulation would be inhibited.
None of the treatments blocked total synthesis of fsh or lh within the 10-day treatment period. ICI 33828 at 100 mg blocked fsh release early in the cycle but 50 mg did not. Oestrogen also blocked fsh release early in the cycle. All follicle growth greater than 4 mm diameter was effectively inhibited by oestrogen and the corpora lutea were maintained. Both progesterone and ICI 33828 reduced the number of follicles growing larger than 5 mm as compared to the control gilts. All treatments blocked fsh release late in the cycle.
There were increased levels of pituitary lh in ICI 33828-treated gilts compared to progesterone-treated gilts early in the cycle, but none of the treatments caused differences in lh levels from those found in the control gilts early in the cycle. All treatments blocked pituitary lh release late in the oestrous cycle.
The pituitary content of prolactin did not differ significantly between treatments.
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