Effect of oestradiol treatment during GnRH-induced ovulation on subsequent PGF2alpha release and luteal life span in anoestrous ewes.
In sheep, induction of ovulation during anoestrus is accompanied by a high incidence of short luteal phases, though pre-treatment with progesterone can overcome this problem. We have investigated the effects of supplementing oestradiol during GnRH-induced ovulation on subsequent PGF2alpha release and luteal life span. Thirty anoestrous crossbred ewes received 250 ng GnRH i.v. at 2 h intervals for 48 h to induce ovulation either alone (group 1; n=10) or in association with either an i.m. injection of 20 mg progesterone 3 days earlier (group 2; n=10) or 3 i.m. injections of 10 microg oestradiol at 8 h intervals on the second day of GnRH treatment (group 3; n=10). Laparoscopy, performed 3 days following GnRH to confirm ovulation and 8 days later, coupled with plasma progesterone analysis were used to determine luteal life span. On day 4 following GnRH, plasma samples were collected at 20 min intervals for 8 h to monitor PGF2alpha release. One ewe from group 1 failed to ovulate and was excluded from further analysis. All groups showed an increase (P<0.01) in plasma oestradiol during GnRH treatment, with group 3 showing a marked (P<0.001) increase over that seen in the other two groups. In group 1 there were 1.4+/-0.2 PGF2alpha episodes/ewe/8 h. In group 2, pre-treatment with progesterone caused the complete inhibition of PGF2alpha episodes (0 episodes/ewe/8 h) while in group 3, treatment with oestradiol resulted in a significant reduction (0.3+/-0.1 episodes/ewe/8 h) compared with group 1 (P<0.01). In group 1, 9/9 ewes exhibited short cycles compared with 2/10 ewes in group 2 (P<0.01). In group 3 the proportion of ewes showing short cycles 7/10 ewes was not significantly different from the other groups. While treatment with oestradiol caused a significant attenuation of PGF2alpha release, this was associated with only a partial reduction in the incidence of short cycles.
Mann
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GE
Division of Animal Physiology, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, LE12 5RD, Leics, UK. george.mann@nottingham.ac.uk
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D000780:Anestrus; D000818:Animals; D003338:Corpus Luteum / Q000502:physiology*; D015237:Dinoprost / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism*; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage*; D010062:Ovulation Induction; D011374:Progesterone / Q000097:blood; D012756:Sheep / Q000502:physiology*
C008228:15-keto-13,14-dihydroprostaglandin F2alpha; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D015237:Dinoprost