title: Response of ewes to a single injection of an analogue of PGF-2 alpha given at different stages of the oestrous cycle.
abstract: Six groups of 4 ewes were given a single i.m. injection of 100 microgram ICI 80,996 on Days 3, 5, 8, 11, 14 or 16 of the oestrous cycle. On day 3 treatment was only partly effective in causing luteal regression, with only 2 of the 4 treated ewes returning to oestrus. Injection had no apparent effect when given on Day 16, at a time when luteal regression had already started naturally. However, treatment between Days 5 and 14 inclusive of the oestrous cycle evoked a rapid fall in progesterone concentrations to basal values of less than 0.5 ng/ml within 24 h with a high degree of synchrony in the return of oestrus (37.7 +/- 1.6 h) and the timing of the LH peak (45.3 +/- 3.2 h) after injection. We conclude that the corpus luteum of the ewe is responsive to ICI 80,996 only between Days 5 and 14 of the oestrous cycle.
mesh_terms: D000818:Animals; D004971:Estrus / Q000187:drug effects*; D004973:Estrus Synchronization; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood; D011247:Pregnancy; D011374:Progesterone / Q000097:blood; D011461:Prostaglandins F, Synthetic / Q000494:pharmacology*; D012756:Sheep / Q000097:blood / Q000502:physiology*
chemical_list: D011461:Prostaglandins F, Synthetic; D011374:Progesterone; D007986:Luteinizing Hormone