The effects of progesterone (P4) on ovarian follicular growth and reproductive endocrinology were studied. Fourteen ewes, synchronized using prostaglandin (PGF2alpha ), were randomly divided in two groups (n=7/group); control group and progesterone-treated group (CIDR) after ovulation (day zero). From one day before PG injection until day 10, daily ultrasonic examinations were done to establish follicular growth. Blood samples for P4 plasma concentration determinations were collected from one day before PG until day 10 post-ovulation. For profile of LH pulses, blood samples were collected at 30-min intervals for a period of 8h on days one and six. The growth rate was different between groups (P<0.001), being 0.91±0.15 and 0.70±0.16mm/d for control and treated-group, respectively. The lengthened of the static phase for control and treated group were 1.9±0.72 and 2.9±0.45d (P<0.05), respectively. Mean concentrations of P4 (P<0.001) were different between treatments. Differences in LH pulse frequency on day one (P<0.01) were observed with values of 2.55±0.09 pulses/8 h in control group and 1.49±0.11 pulses/8h in treated-group. On day six, control group showed higher values for LH pulse frequency (2.20±0.09 pulses/8h) than treated-group (P<0.05), (1.22±0.11 pulses/8h). In conclusion, the inhibitory effects of exogen P4 on the diameter of dominant follicle was mediated by reduced LH pulse frequency.
sheep; follicular dynamic; LH; ovulation; progesterone
