title: Exogenous progesterone: influence on ovulation and hormone levels in the cyclic hamster.
abstract: The oestrous cycle of the hamster is lengthened by 2 to 3 days when 2-5 or 5-0 mg progesterone are injected on day 1 of the cycle (day of ovulation). Antral follicles develop on day 2 but their growth is significantly retarded in progesterone-treated hamsters. Administration of progesterone is followed within 6 h by an abrupt decline in serum FSH and LH concentration but by day 3 the level of FSH is higher than normal. Serum LH is slower to recover in hamsters receiving 5 mg progesterone but normal levels are also restored by days 3 or 4. Increased serum levels of progesterone are maintained until days 3-5 in animals injected with progesterone. Despite the presence of antral follicles on day 2 and the fairly prompt restoration of normal levels of gonadotrophins, the serum concentration of oestradiol is suppressed for several days in the progesterone-treated hamster. This suggests that progesterone, in addition to affecting the hypothalamic-pituitary system, may also directly inhibit oestrogen secretion by the antral follicles.
mesh_terms: D000818:Animals; D006224:Cricetinae; D004958:Estradiol / Q000097:blood; D004971:Estrus / Q000187:drug effects*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood*; D007986:Luteinizing Hormone / Q000097:blood*; D011247:Pregnancy; D011374:Progesterone / Q000097:blood / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone