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This Article Full Text Full Text (PDF) All Versions of this Article: 68/4/1403    most recent biolreprod.102.007278v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bartlewski, P. M. Articles by Rawlings, N. C. Search for Related Content PubMed PubMed Citation Articles by Bartlewski, P. M. Articles by Rawlings, N. C. Agricola Articles by Bartlewski, P. M. Articles by Rawlings, N. C.

Effects of a 6-Day Treatment with Medroxyprogesterone Acetate after Prostaglandin F₂-Induced Luteolysis at Midcycle on Antral Follicular Development and Ovulation Rate in Nonprolific Western White-Faced Ewes¹

^a Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

Medroxyprogesterone acetate (MAP) from intravaginal sponges prolongs the lifespan of large ovarian follicles when administered after prostaglandin F₂ (PGF₂)-induced luteolysis early in the luteal phase of ewes. The present study was designed to determine whether a PGF₂/MAP treatment applied at midcycle would alter the pattern of antral follicle growth and increase ovulation rate in nonprolific ewes. A single injection of PGF₂ (15 mg, i.m.) was given, and an intravaginal MAP (60 mg) sponge was inserted for 6 days, on Day 8 after ovulation, in 7 (experiment 1), 8 (experiment 2) or 11 (experiment 3) ultrasonographically monitored, cycling Western white-faced ewes; seven ewes (experiment 1) served as untreated controls. Blood samples were collected each day and also every 12 min for 6 h, halfway through the period of treatment with MAP (experiment 1), or every 4 h, from 1 day before to 1 day after sponging (experiment 2). Seventeen of 26 treated ewes (experiment 1, n = 6; experiment 2, n = 5; experiment 3, n = 6) ovulated 1 to 6 days after PGF₂, but this did not affect the emergence of ensuing follicular waves (experiments 1 and 2). These ovulations, confirmed by laparotomy and histological examinations of the ovaries (experiment 3), were not preceded by an increase in LH/FSH secretion and did not result in corpora lutea, as evidenced by transrectal ultrasonography and RIA of serum progesterone (experiments 1 and 2). Following the removal of MAP sponges, the mean ovulation rate was 3.1 ± 0.4 in treated ewes and 2.0 ± 0.3 in control ewes (experiment 1; P < 0.05). In experiments 1 and 2, the ovulation rate after treatment (3.1 ± 0.4 and 2.8 ± 0.4) was also greater than the pretreatment rate (1.9 ± 0.3 and 1.9 ± 0.1, respectively). Ovulations of follicles from two consecutive waves before ovulation were seen in five treated but only in two control ewes (experiment 1), and in seven ewes in experiment 2. There were no significant differences between the MAP-treated and control ewes in mean daily serum concentrations of FSH and estradiol, and no differences in the parameters of LH/FSH secretion, based on frequent blood sampling. Treatment of nonprolific Western white-faced ewes with PGF₂ and MAP at midcycle changed follicular dynamics and increased ovulation rate by approximately 50%. These effects of MAP, in the absence of luteal progesterone, may not be mediated by changes in gonadotropin secretion.

¹ This study was funded by the Alberta Agricultural Research Institute (AARI) in the form of a Farming for the Future grant to N.C.R. and by the Natural Sciences and Engineering Council of Canada (NSERC). P.M.B. was supported by a University of Saskatchewan Graduate Scholarship and Saskatchewan Health Services Utilization and Research Commission postdoctoral fellowship.

² Correspondence: N.C. Rawlings, Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK, Canada S7N 5B4. FAX: 306 966 7376; norman.rawlings{at}usask.ca

³ Current address: Department of Obstetrics, Gynecology and Reproductive Sciences, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada S7N 5B4

⁴ Current address: Human Health Research Center, INRS-Institut Armand Frappier, Quebec City, QC, Canada H7V 1B7

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