J Androl 2001; 22: 54–61.
Editorial comment: The importance of nitric oxide (NO) as a major mediator of penile erection is presently well established in the medical literature. Descriptions of NO biology in the penis have centered mainly on the neuronal isoform of NO synthase (nNOS or NOS I), which is believed to be the primary source of the chemical for mediation of the physiological response. However, relatively little information has been gathered regarding the role of the endothelial isoform, which also synthesizes NO (eNOS or NOS III) in penile erection. In light of this shortcoming and the additional observation that NOS I gene (not protein) expression has not been confirmed in the penis, these investigators performed a comprehensive analysis of both NOS I and III isoforms in the normal rat penis. They demonstrated that both NOS I and III gene and protein products are expressed in the rat penis, with NOS I localizations to neuronal constituents and NOS III localizations to endothelium and cavernosal smooth muscle. Furthermore, using competitive quantitative reverse transcription-polymerase chain reaction techniques, they showed greater NOS III than NOS I gene expression in the penile shaft. This study highlights the redundancy of NO sources of formation in the penis and additionally suggests that the functional role of NOS III in mediating penile erection is probably quite significant. Subsequent studies further elucidating the specific functional effects of NOS III in the penis will be particularly helpful in this regard.
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Burnett, A., Gonzalez, C., Brannigan, R. et al. Protein and gene expression of nitric oxide synthase isoforms I and III in the rat penile shaft. Int J Impot Res 14, 316 (2002). https://doi.org/10.1038/sj.ijir.3900850