Rats endocrine system rat 208 Animal 170 animal experiment 156 Male 132 Rats, Inbred Strains 130 nonhuman 122 Support, Non-U.S. Gov't 118 radioisotope 118 Female 114 animal cell 72 central nervous system 68 drug efficacy 58 priority journal 58 Castration 56 Pineal Gland 52 Animals 50 female genital system 50 pineal body 50 Estradiol 46 estradiol 46 Prolactin 44 prolactin 42 article 40 autonomic nervous system 38 Kinetics 36 drug comparison 36 male genital system 36 Ganglia, Sympathetic 34