Aim:To investigate the effect of icariin on erectile function and the expression of nitric oxide synthase (NOS)isoforms in castrated rats.Methods:Thirty-two adult male Wistar rats were randomly divided into one sham-operated group (A) and three castrated groups (B,C and D).One week after surgery,rats were treated with normalsaline (groups A and B) or oral icariin (1 mg/[kg-day] for group C and 5 mg/[kg.day] for group D) for 4 weeks.Oneweek after treatment,the erectile function of the rats was assessed by measuring intracavernosal pressure (ICP)during electrostimulation of the cavernosal nerve.The serum testosterone (ST) levels,the percent of smooth muscle(PSM) in trabecular tissue,and the expression of mRNA and proteins of neuronal nitric oxide synthase (nNOS),inducible nitric oxide synthase (iNOS),endothelial nitric oxide synthase (eNOS) and phosphodiesterase V (PDE5) incorpus cavernosum (CC) were also evaluated.Results:ICP,PSM,ST and the expression of nNOS,iNOS,eNOSand PDE5 were significantly decreased in group B compared with those in group A (P<0.01).However,ICP,PSMand the expression of nNOS and iNOS were increased in groups C and D compared with those in group B (P<0.05).Changes in ST and the expression of eNOS and PDE5 were not significant (P>0.05) in groups C and D comparedwith those in group B.Conclusion:Oral treatment with icariin (>98.6 % purity) for 4 weeks potentially improveserectile function.This effect is correlated with an increase in PSM and the expression of certain NOS in the CC ofcastrated rats.These results suggest that icariin may have a therapeutic effect on erectile dysfunction.(Asian JAndrol 2005 Dec;7:381-388) Aim: To investigate the effect of icariin on erectile function and the expression of nitric oxide synthase (NOS)isoforms in castrated rats.Methods:Thirty-two adult male Wistar rats were randomly divided into one sham-operated group (A) and three castrated Groups (B,C and D).One week after surgery,rats were treated with normalsaline (groups A and B) or oral icariin (1 mg/[kg-day] for group C and 5 mg/[kg.day] for Group D) for 4 weeks.Oneweek after treatment,the erectile function of the rats was assessed by measuring intracavernosal pressure (ICP) during electrostimulation of the cavernosal nerve.The serum testosterone (ST) levels,the percent of smooth muscle(PSM) in Trabecular tissue,and the expression of mRNA and proteins of neuronal nitric oxide synthase (nNOS),inducible nitric oxide synthase (iNOS),endothelial nitric oxide synthase (eNOS) and phosphodiesterase V (PDE5) incorpus cavernosum (CC) were also evaluated.Results :ICP,PSM,ST and the expression of nNOS,iNOS,eNOSand PDE5 were sign Ificantly decreased in group B compared with those in group A (P<0.01).However,ICP,PSM and the expression of nNOS and iNOS were increased in groups C and D compared with those in group B (P<0.05).Changes in ST And the expression of eNOS and PDE5 were not significant (P>0.05) in groups C and D compared with those in group B.Conclusion:Oral treatment with icariin (>98.6 % purity) for 4 weeks possible improveerectile function.This effect is correlated with An increase in PSM and the expression of certain NOS in the CC ofcastrated rats.These results suggest that icariin may have a therapeutic effect on erectile dysfunction. (Asian JAndrol 2005 Dec;7:381-388)