progesterone blood level Female 26 controlled study 26 progesterone 26 Animals 24 female 24 nonhuman 24 priority journal 24 rat 24 animal experiment 22 Ovary 20 Rats 20 Rats, Sprague-Dawley 20 article 20 animal tissue 18 protein expression 18 Progesterone 14 steroidogenesis 14 Western blotting 12 apoptosis 12 Apoptosis 10 Blotting, Western 10 Gonadotropins, Equine 10 animal cell 10 chorionic gonadotropin 10 corpus luteum 10 estradiol 10 ovary follicle 10 Corpus Luteum 8 Leuprolide 8