Male Rats Rats, Inbred Strains animal experiment rat 118 Animal 98 Support, Non-U.S. Gov't 84 nonhuman 68 endocrine system 66 radioisotope 44 article 34 priority journal 34 male 32 Female 28 intraperitoneal drug administration 28 autonomic nervous system 26 animal cell 24 central nervous system 24 pineal body 24 propranolol 24 Animals 22 Ganglia, Sympathetic 22 Norepinephrine 22 Pineal Gland 22 Prolactin 22 drug efficacy 22 noradrenalin 20 Castration 18 controlled study 18 in vitro study 18