Ovarian and Pituitary Hormones in Blood of Progestogen-Treated Ewes

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Abstract
Estradiol (E2), estrone (E1), progesterone, LH and prolactin concentrations were determined by radioimmunoassay in blood plasma samples from parous ewes treated with medroxyprogesterone acetate (MAP) or melengestrol acetate (MGA) orally, with MAP by intravaginal sponge, or progesterone by intramuscular injection. Treatment was begun on Day 10 of the estrous cycle and continued for 14 days. Blood samples were collected daily from Day 10 through 13 of the estrous cycle for untreated ewes and from Day 10 through 23 for progestogen-treated ewes, after which the frequency of blood collection was increased to 6-hr intervals until 48 hr after the beginning of estrus. Corpora lutea (CL) regressed, as indicated by a reduction of plasma progesterone concentration, between Day 13 and 15 of the estrous cycle. As soon as the CL regressed, LH (P<.01) and E2 concentrations increased linearly with time in untreated ewes and in ewes still under treatment with MGA or MAP orally or with progesterone intramuscularly. The increases were not found in ewes treated with MAP intravaginally. After termination of progestogen treatments on Day 23, plasma E2 increased (P<.01) further, followed by a LH surge 73.8 ± 3.3 hr after the last progestogen administration. For the untreated ewes, E2 concentrations rose sharply (from 5.8 pg/ml to 22.0 pg/ml) during the 48-hr period before the preovulatory LH surge; this E2 secretion for untreated ewes (response slope of 5.4) differed (P<.01) from those of the progestogen-treated ewes (response slopes of 1.8 to −.4). Estrone secretion paralleled E2, but the E1 concentrations were about one-third of the magnitude. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science.