Circulating gonadotrophins and follicular dynamics in anestrous ewes after treatment with estradiol-17β

Plasma FSH, LH, estradiol (E2) and progesterone (P4) profiles and patterns of follicular growth and regression by ultrasonography were determined after E2 treatment (1 μg/kg) in anestrous ewes. Fifteen ewes were treated with one (group I, n=7) or two (group II, n=4) i.m. injections of E2 with a 24 h interval, or two oil injections with a 24 h interval (group C, n=4). Blood samples for E2, P4, FSH and LH determinations were collected daily 4 days before the initiation of the treatment (day 0), when bleeding increased to every 2 h starting 2 h before treatment until 56 h after the first injection and from then on every 6 h until day 8, and twice per day till the end of the experiment (day 9). During the experimental period (days −4 to 9), transrectal ultrasonic examinations were carried out daily using a 7.5 MHz linear array probe. Number and size of follicles ≥3 mm in diameter were recorded. No estrous was detected before, during or after treatment. LH and FSH surges were observed 10–18 h after the first E2 injection. The second E2 injection stimulated another release of LH but no surges. E2 inhibited FSH levels before the surge and the second E2 injection induced a longer inhibition. No ovulation was detected by ultrasonography during the experimental period and P4 levels remained low (<0.7 nmol/l) before, during and after the treatment in all ewes. There was an effect of E2 treatment on the diameter of the largest follicle, a decrease could be observed 3 days after the first injection in both ewes of groups I and II. The E2-treated groups had a higher frequency of ewes showing wave emergence on day 3 (day 1.5±1, 2.4±0.4 and 2.5±0.5 for control, groups I and II). LH and FSH surges were observed after E2 treatment, but were not able to provoke ovulation neither luteinization. In contrast, the treatment was associated with the regression of the largest follicle and with emergence of a new follicular wave on day 3.