Protein and gene expression of nitric oxide synthase isoforms I and III inthe rat penile shaft

Nitric oxide synthase (NOS) plays a key role in penile smooth muscle relaxa tion through the regulation of nitric oxide (NO). NO is a major neurotransm itter in the autonomic nervous system, and alteration of its activity has b een implicated in erectile dysfunction. The objectives of this study were t wofold: 1) to demonstrate and localize the NOS protein isoforms I and III i n the normal rat penis, and 2) to identify and quantitate NOS I and III gen e expression in the normal rat penis. The gene and protein product of NOS i soforms I and III are expressed in rat penile tissue. Protein expression of NOS I was confined primarily to neuronal tissue. while NOS III protein exp ression was identified primarily in both cavernosal smooth muscle and endot helium. The presence of both NOS I and III was confirmed in the penile shaf t by Western blot. Quantitation of NOS I and III gene expression by reverse transcription-polymerase chain reaction revealed NOS Ill to be more highly expressed than that of NOS I in the rat penile shaft. NOS I and III protei n and gene products are both expressed in normal rat penile tissue. Protein expression is localized primarily to neuronal tissue for NOS I, whereas NO S ill is localized primarily to cavernosal smooth muscle and endothelium. N OS ill gene expression Is greater than that of NOS I in the normal rat peni le shaft. These findings support the possibility that penile erection is re gulated by different NOS isoforms released from neural, endothetial, and sm ooth muscle sources.