nitric oxide synthase nonhuman 54 priority journal 50 controlled study 49 article 48 enzyme activity 39 nitric oxide 39 Animals 37 animal tissue 37 animal experiment 36 Nitric Oxide Synthase 29 animal model 25 female 25 male 25 Male 23 rat 22 signal transduction 21 Female 20 Nitric Oxide 20 Nitric oxide synthase 20 mouse 20 protein expression 20 enzyme activation 16 animal cell 15 Mice 14 Nitric oxide 14 Signal Transduction 14 progesterone 12 Cyclic GMP 11 Rats 11