Effects of an LHRH antagonist on gonadotrophin and oestradiol secretion, follicular development, oestrus and ovulation in Holstein heifers.
Mature cyclic Holstein heifers were given a luteolytic dose of cloprostenol followed by two i.v. injections, 12 h apart, of various doses of [Ac-D-Nal1, D-p-Cl-Phe2, D-Trp3, D-Arg6, D-Ala10]-LHRH, beginning either at the time of first observation of behavioural oestrus, or 48 h after the cloprostenol injection. When treatment began at the first observation of oestrus, the time of ovulation, as determined by ultrasonic echography, was significantly delayed by total doses of 0.8 mg or more of the antagonist. When given at 48 and 60 h after cloprostenol injection, a total dose of 1.5 mg of the antagonist significantly delayed the growth of the ovulating follicle, the onset of oestrus, the preovulatory surges of oestradiol, LH and FSH, and ovulation. It is concluded that the LHRH antagonist can effectively suppress endogenous LH secretion and may therefore be useful in the study of follicular development, ovulation, and other events in the oestrous cycle of the cow.
Rieger
D
D
Centre de recherche en reproduction animale, Faculté de médecine vétérinaire, Université de Montréal, St-Hyacinthe, Québec, Canada.
Roberge
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S
Coy
D H
DH
Rawlings
N C
NC
D000818:Animals; D002417:Cattle / Q000502:physiology*; D003008:Cloprostenol / Q000494:pharmacology; D004958:Estradiol / Q000378:metabolism*; D004971:Estrus / Q000187:drug effects; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D006062:Gonadotropins / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000378:metabolism; D006080:Ovarian Follicle / Q000187:drug effects / Q000502:physiology; D010060:Ovulation / Q000187:drug effects; D012098:Reproduction / Q000187:drug effects*
D006062:Gonadotropins; D007987:Gonadotropin-Releasing Hormone; D003008:Cloprostenol; D004958:Estradiol; C060521:LHRH, N-Ac-naphthyl(1)-(4-Cl-Phe)(2)-Trp(3)-Arg(6)-Ala(10)-; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone