Objective To cladfy the dependence of neural nitric rnoxide synthase mRNA (nNOSmRNA) and endothelial rnnitric oxide synthase mRNA (eNOSmRNA) on rnandrogens (testosterone [T] and dihydrotestosterone rn[DHT]).rnMethods 160 male Sprague Dawley (SD) rats were rndivided into Groups A (56 rats, 5 weeks old), B (50rnrets,10 weeks old) and C (54 rats, 58 weeks old).rnGroups A, B and C were all subdivided respectively rninto five Subgroups. Subgroup 1: intact osntrels;rnSubgroup 2: castrated; Subgroup 3: castrated with rntestosterone ubdecanoate 25 mg/kg·mon-1,rnintramuscular injection, Subgroup 4: castrated with rntestosterone undecanoate 50 mg/kg·mon-1,rnintramuscular injection and Subgroup 5: treated with rnfinaeteride 4.5 mg/kg·day-1, orally. Four and ten rnweeks after treatments described above, one half of rnthe rats were killed. Serum samples were token for rnmeasurements of T, free testosterone (FT) and DHT rnby raclioimmunoassay. Penile samples were treated rnwith liquid nitrogen and then stored at-80℃.rnnNOSmRNA and eNOSmRNA were detected by rnsemiquantitative reveres-transcription polymerase chain rnreaction (RT-PCR) and Dot blot.rnResulte There was no significant difference between rnSubgroup 1 and Subgroup 2 or Subgroup 5 in all rnGroups A, B and C. The expression of penile rneNOSmRNA of Group A was significantly increased (4 rnweeks model) (P＜0.05) or increased (10 weeks rnmodel) (P＞0.05) in Subgroup 2 or 5 compared with rnthose in Subgroup 1.There wes no significant rndifference between Subgroup 1 and Subgroup 2 or rnSubgroup 5 of Group B in 4 weeks model (P＞0.05).rnThere was an elevation when animals were castrated or rntreated with finasteride in the 10 weeks model.The rnexpreseion of penile eNOSmRNA of Group C was rnsignificantly increased (10 weeks model) (P＜0.05)rnor increased (4 weeks model) in Subgroup 2 compared rnwith those in Subgroup 1.The production of rneNOSmRNA in Subgroup 5 was also increased rn(including 4- and 10-week models). When T was rnsupplied for castration, the penile eNOSmRNA was rndesreased to some extent; the greater the dose of T rngiven, the lower penile eNOSmRNA was observed.rnConclusions The expression of eNOSmRNA in SD rnrat penile tissue increases while T or DHT diminishes.rnSometimes androgens medaulate penile eNOSmRNA in rnopposite directions. There is no srrelation between thernexpression of nNOSmRNA and androgens (including Trnand DHT) . Androgens give rise to penile erectionrnprobably not via the NOS pathway.