Androgen Receptor Signaling is Similar in Human Corpus Cavernosum in Men with Different Serum Testosterone Levels.

ABSTRACT

BACKGROUND: Testosterone (T) plays an important role in male reproductive function and tissue development. Normal serum T levels vary between 300 and 1000 ng/dl. It is not known, however, if varying serum T levels alter androgen receptor (AR) signaling in tissue. OBJECTIVE: To measure AR signaling levels in human corpus cavernosal tissue in males with different serum T levels. DESIGN, SETTING, AND PARTICIPANTS: Participants were selected from a group of males undergoing surgical management for erectile dysfunction (ED; penile prosthesis placement). T levels were measured 1 week before surgery and a sample of corpus cavernosal tissue was procured during surgery. The tissue was homogenized, measured for protein concentration, and used for western blot analysis. VEGF was selected as an AR marker and actin was used for protein normalization. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: VEGF and actin expression levels were analyzed using western blot analysis and ImageJ was used for quantification of antibody expression. RESULTS AND LIMITATIONS: AR signaling was measured in terms of VEGF expression. Above a T level of 200 ng/dl, there was no significant difference found in VEGF expression. Only one patient had a T level less than 200 ng/dl, limiting the generalizability of these results. In addition, all patients had a history of ED, and controls (patients without ED) were not included in the study. CONCLUSIONS: Above a serum T level of 200 ng/dl, there was no significant difference in AR signaling. This finding suggests that there could be a saturation level present in corpus cavernosal tissue that is approximately 200 ng/dl. PATIENT SUMMARY: Serum testosterone levels above a certain threshold may not be necessary for biological functions. Instead, it is most likely that there is an approximate serum testosterone level that fully saturates tissue androgen receptors and results in peak function in men.