title: Response of seasonally anoestrous ewes to small-dose multiple injections of Gn-RH with and without progesterone pretreatment.
abstract: Four groups, each of 5 seasonally anoestrous ewes, were treated i.v with small doses (75, 125, 250 or 500 ng) of Gn-RH at 2-h intervals for 48 h. A further 15 ewes received 14 days pretreatment with progesterone and then the 250 ng Gn-RH treatment. Gn-RH injections induced an episodic pattern of LH secretion which differed significantly for the doses of Gn-RH used. A preovulatory LH surge occurred in all but 1 of the ewes during the period of Gn-RH treatment. Ovulation occurred in all 15 ewes pretreated with progesterone and in 19/20 ewes treated with Gn-RH alone. Although normal luteal function occurred in all ewes pretreated with progesterone, it was present in only 5 of the 20 ewes treated with Gn-RH alone. Oestrus, as shown by mating, occurred at a mean time of 34.7 +/- 2.6 h after the start of Gn-RH treatment only in those ewes receiving progesterone pretreatment. These results indicate that progesterone pretreatment has a marked effect on the ability of small doses of Gn-RH to induce ovulation and normal luteal function in seasonally anoestrous ewes.
mesh_terms: D000780:Anestrus / Q000187:drug effects; D000818:Animals; D003338:Corpus Luteum / Q000187:drug effects; D004334:Drug Administration Schedule; D004971:Estrus / Q000187:drug effects; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood; D010906:Pituitary Hormone-Releasing Hormones / Q000008:administration & dosage / Q000494:pharmacology*; D011247:Pregnancy; D011374:Progesterone / Q000097:blood / Q000494:pharmacology*; D012756:Sheep
chemical_list: D010906:Pituitary Hormone-Releasing Hormones; D011374:Progesterone; D007986:Luteinizing Hormone