Response of the 1-5 day-aged ovine corpus luteum to prostaglandin F2alpha.
The hypothesis that, in the ewe, prostaglandin (PG) F2alpha administration on day 3 after ovulation is followed by luteolysis and ovulation was tested using 24 animals. The ewes were treated with a dose of a PGF2alpha analogue (delprostenate, 160 microg) on days 1 (n=8), 3 (n=8) or 5 (n=8) after ovulation, was established by transrectal ultrasonography. Daily scanning and blood sampling were performed to determine ovarian changes and progesterone serum concentrations by radioinmunoassay. The treatment induced a sharp decrease of progesterone concentrations followed by oestrus and ovulation in all ewes treated on days 3 and 5 and in one ewe treated on day 1 (8/8, 8/8, 1/8; P<0.05). Seven ewes treated on day 1 did not respond to PGF2alpha treatment and had an inter-ovulatory cycle of normal length (17.4 +/- 0.5 days). However, the profile of progesterone concentrations during the cycle of these ewes was delayed 1 day (P<0.05) compared with a control cycle. The overall interval between PGF2alpha and oestrus for the 17 responding ewes was 42.4 +/- 2.3 h. In 15 of these ewes the ovulatory follicle was originated from the first follicular wave and the ovulation occurred at 60.8 +/- 1.8 h after PGF2alpha treatment. The other two responding ewes ovulated an ovulatory follicle originated from the second follicular wave between 72 and 96 h after treatment. These results support the hypothesis and suggest that refractoriness to PGF2alpha of the recently formed corpus luteum (CL) may be restricted to the first 1-2 days post-ovulation.
Rubianes
E
E
Department of Animal Production, Faculty of Agriculture, Lasplaces 1550, Montevideo, Uruguay. rubianes@adinet.com.uy
Menchaca
A
A
Carbajal
B
B
D000818:Animals; D003338:Corpus Luteum / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000502:physiology; D015237:Dinoprost / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004971:Estrus; D005260:Female; D007700:Kinetics; D006080:Ovarian Follicle / Q000502:physiology; D010060:Ovulation; D011374:Progesterone / Q000097:blood; D011461:Prostaglandins F, Synthetic / Q000494:pharmacology*; D012756:Sheep; D013997:Time Factors; D014463:Ultrasonography
D011461:Prostaglandins F, Synthetic; D011374:Progesterone; D015237:Dinoprost; C050851:delprostenate