Does injection of prostaglandin F(2alpha) (PGF2alpha) cause ovulation in anestrous Western White Face ewes?
In a previous study in our laboratory, treatment of non-prolific Western White Face (WWF) ewes with PGF(2 alpha) and intravaginal sponges containing medroxyprogesterone acetate (MAP) on approximately Day 8 of a cycle (Day 0 = first ovulation of the interovulatory interval) resulted in ovulations during the subsequent 6 days when MAP sponges were in place. Two experiments were performed on WWF ewes during anestrus to allow us to independently examine if such ovulations were due to the direct effects of PGF(2 alpha) on the ovary or to the effects of a rapid decrease in serum concentrations of progesterone at PGF(2 alpha)-induced luteolysis. Experiment 1: ewes fitted with MAP sponges for 6 days (n = 12) were injected with PGF(2 alpha) (n = 6; 15 mg im), or saline (n = 6) on the day of sponge insertion. Experiment 2: ewes received progesterone-releasing subcutaneous implants (n = 6) or empty implants (n = 5) for 5 days. Six hours prior to implant removal, all ewes received a MAP sponge, which remained in place for 6 days. Ewes from both experiments underwent ovarian ultrasonography and blood sampling once daily for 6 days before and twice daily for 6 days after sponge insertion. Additional blood samples were collected every 4 h during sponge treatment. Experiment 1: 4-6 (67%) PGF(2 alpha)-treated ewes ovulated approximately 1.5 days after PGF(2 alpha) injection; these ovulations were not preceded by estrus or a preovulatory surge release of LH, and resulted in transient corpora hemorrhagica (CH). The growth phase was longer (P < 0.05) and the growth rate slower (P < 0.05) in ovulating versus non-ovulating follicles in PGF(2 alpha)-treated ewes. Experiment 2: in ewes given progesterone implants, serum progesterone concentrations reached a peak (1.7 2 ng/mL; P < 0.001) on the day of implant removal and decreased to basal concentrations (<0.17 ng/mL; P < 0.001) within 24 h of implant removal. No ovulations occurred in either the treated or the control ewes. We concluded that ovulations occurring after PGF(2 alpha) injection, in the presence of a MAP sponge, could be due to a direct effect of PGF(2 alpha) at the ovarian level, rather than a sudden decline in circulating progesterone concentrations.
Davies
K L
KL
Department of Veterinary Biomedical Sciences, WCVM, University of Saskatchewan, 52 Campus Drive, Saskatoon, Sask., Canada S7N 5B4.
Bartlewski
P M
PM
Epp
T
T
Duggavathi
R
R
Barrett
D M W
DM
Bagu
E T
ET
Cook
S J
SJ
Rawlings
N C
NC
D000780:Anestrus; D000818:Animals; D003271:Contraceptive Agents, Female / Q000494:pharmacology*; D015237:Dinoprost / Q000494:pharmacology*; D004343:Drug Implants; D005260:Female; D007273:Injections, Intramuscular / Q000662:veterinary; D007986:Luteinizing Hormone / Q000097:blood; D003341:Luteolysis; D017258:Medroxyprogesterone Acetate / Q000494:pharmacology; D006080:Ovarian Follicle / Q000187:drug effects* / Q000502:physiology; D010060:Ovulation / Q000187:drug effects*; D010062:Ovulation Induction / Q000379:methods / Q000662:veterinary; D011374:Progesterone / Q000097:blood*; D011897:Random Allocation; D012756:Sheep / Q000097:blood / Q000502:physiology*
D003271:Contraceptive Agents, Female; D004343:Drug Implants; D011374:Progesterone; D007986:Luteinizing Hormone; D015237:Dinoprost; D017258:Medroxyprogesterone Acetate