Corpus Luteum Response to 6-chloro Δ6-17 acetoxyprogesterone and HCG in the Cow

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Abstract
An in vivo-in vitro incubation system was used to evaluate the effects of 6-chloro Δ6-l7 acetoxyprogesterone (CAP) and HCG on bovine corpus luteum (CL) growth and progesterone synthesis. Corpora lutea were removed from 15 heifers in three consecutive estrous cycles. Progesterone concentration and CL size were not affected by repeated CL removal. Variations in progesterone values for CLs within animals were similar to that between animals. Weight of corpora lutea formed after a CAP-synchronized estrus was equal to controls while progesterone concentration was increased. HCG, administered daily from Day 2 to Day 7 of the estrous cycle significantly (p < 0.01) increased CL size; however, these CLs were less responsive to in vitro HCG stimulation than control or CAP CLs. HCG given in single injections (1000 IU) on either Day 1 or 3 of an estrous cycle also significantly increased CL size. Progesterone concentration was not markedly altered in the larger CLs, but the total content of progesterone was significantly increased.

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