Rats 130 Rats, Inbred Strains endocrine system 130 rat 130 Animal 100 animal experiment 92 nonhuman 90 Male 84 Support, Non-U.S. Gov't 84 Female 64 radioisotope 64 animal cell 52 drug efficacy 44 priority journal 42 Castration 34 central nervous system 34 Pineal Gland 32 female genital system 32 Animals 30 pineal body 30 Norepinephrine 28 autonomic nervous system 28 Estradiol 24 Progesterone 24 Prolactin 24 Prostaglandins E 24 drug receptor binding 24 Ganglia, Sympathetic 22 In Vitro 22 Testosterone 22