Effect of continuous infusion of gonadotrophin-releasing hormone in ewes at different times of the year.
Gn-RH (3 mug/hr for 8 hr) evoked a surge of LH in ewes during the anoestrous season which was of similar peak height to that found at oestrus but of shorter duration. When Gn-RH was given on 3 consecutive days, the response was considerably reduced on the 2nd and 3rd day. Follicles grew as a result of Gn-RH infusion but peripheral plasma oestrogen concentration did not increase. During the anoestrous season 9/18 ewes ovulated but only 1/6 did so at mid-anoestrus. Mature follicles or a CL were found in 15/18 ewes that had increased peripheral plasma progesterone concentrations for 1-5 days (11 ewes) or 9-14 days (4 ewes). The concentrations of progesterone found were always lower than those observed during the normal cycle. In the breeding season 10/11 ewes ovulated but there was no evidence that the induced CL were maintained.
D000780:Anestrus / Q000187:drug effects; D000818:Animals; D004967:Estrogens / Q000097:blood; D004971:Estrus / Q000187:drug effects; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000097:blood; D010060:Ovulation / Q000187:drug effects; D011247:Pregnancy; D011374:Progesterone / Q000097:blood; D012621:Seasons; D012756:Sheep / Q000502:physiology*
D004967:Estrogens; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D007986:Luteinizing Hormone