drug comparison 44 in vitro study animal experiment 30 rat 30 Rats 28 Animal 26 drug response 22 Male 20 dose response 20 radioisotope 16 endocrine system 14 Norepinephrine 12 Support, Non-U.S. Gov't 12 noradrenalin 12 In Vitro 10 Prostaglandins 10 central nervous system 10 corticosterone 10 nonhuman 10 Animals 8 Pineal Gland 8 Rats, Inbred Strains 8 animal cell 8 drug metabolism 8 inotropism 8 pineal body 8 serotonin 8 Corticosterone 6 Dose-Response Relationship, Drug 6 Drug Interactions 6