Rats article unclassified drug Animals 180 rat 179 nonhuman 178 controlled study 133 priority journal 130 animal cell 105 animal experiment 102 Male 89 Rats, Sprague-Dawley 78 Female 75 animal tissue 73 male 57 female 55 animal 45 protein expression 44 metabolism 41 mouse 40 Animalia 39 Rats, Wistar 39 Humans 38 animal model 38 Mice 37 drug effect 35 human 34 messenger RNA 32 radioisotope 30 Rattus 29