Medroxyprogesterone Acetate: RESULTS(4)
Progesterone concentrations and CL/luteal structures. Mean daily serum concentrations of progesterone for the ewes given PGF2c, and MAP and for control ewes are shown in Figure 2. All treated ewes responded to PGF2a as evidenced by an abrupt decline in circulating concentrations of progesterone and luteal regression observed with ultrasonography. Circulating concentrations of luteal progesterone declined (P < 0.05) to a basal level 24 h after injection of PGF2a and remained low (P > 0.05) during the entire period of treatment with progestogen sponges. Mean serum concentrations of progesterone were significantly higher in control ewes than in treated ewes for 6 consecutive days, from Day 1 to Day 6 after PGF2a.
All CL were detected by Day 4 after ovulation following sponge withdrawal in the treatment group (both groups, 3.3 ± 0.2 days after ovulation; P > 0.05). Three treated ewes and three control animals had fewer Cl than ovulated follicles. A short-lived CL (observed once only on Day 3 after ovulation) was observed in one control ewe, and in this same ewe, a luteinized unovulated follicle was detected. The mean number of all luteal structures per ewe (2.4 ± 0.3 and 1.4 ± 0.2 for treated and control ewes, respectively) differed from the mean ovulation rates (3.1 ± 0.4 and 2.0 ± 0.3 for treated and control ewes, respectively; P < 0.05).
FIG. 1. The diameter profiles of individual antral follicles growing from 3 to >5 mm in two Western white-faced ewes that received PGF2a and a progestogen (MAP) sponge on Day 7 (A) or Day 8 (B) after ovulation, and two control ewes (C, D; experiment 1). Day 0 = day of treatment with PGF2a, Day 6 = day of MAP sponge removal (treated ewes). The arrows along the X-axis (top panels; T) denote the days of follicle wave emergence, and the arrows within the upper chart area (—OV) indicate the ovulatory follicles on the day before ovulation.
FIG. 2. Daily serum concentrations of progesterone (mean ± SEM) during the 19-day study period in seven Western white-faced ewes that received PGF2a injection on —Day 8 and a progestogen (MAP) sponge from — Days 8 to 14 after ovulation (treated ewes, filled symbols), and seven untreated white-faced ewes (control ewes, hollow symbols; experiment 1). Data were aligned to the day of treatment with PGF2a (Day 0) of the treated ewes. *P < 0.05 (data analyzed for the period from 1 day before to 1 day after MAP treatment). See text for additional statistical descriptions.