madman
Super Moderator
ABSTRACT
Background: Testosterone (T) deficiency is associated with erectile dysfunction (ED). The relaxant response of T on the corporal smooth muscle through a non-genomic pathway has been reported; however, the in vitro modulating effects of T on human corpus cavernosum (HCC) has not been studied.
Objectives: To compare the effects of various concentrations of T on nitric oxide (NO)-dependent and - independent relaxation in organ bath studies and elucidate its mode of action, specifically targeting the cavernous NO/cyclic guanosine monophosphate (cGMP) pathway.
Materials and Methods: HCC samples were obtained from men undergoing penile prosthesis implantation (n = 9). After phenylephrine (Phe) precontraction, the effects of various relaxant drugs of HCC strips were performed using an organ bath at low (150ng/dL), eugonadal (400ng/dL), and hypergonadal (600ng/dL) T concentrations. The penile tissue measurements of endothelial nitric oxide synthase (eNOS), neuronal (n)NOS, and phosphodiesterase type 5 (PDE5)A were evaluated via immunostaining, Western blot, cGMP, and nitrite/nitrate (NOx) assays.
Results: Relaxation responses to ACh and EFS in isolated HCC strips were significantly increased at all T levels compared with untreated tissues. The sildenafil-induced relaxant response was significantly increased at both eugonadal and hypergonadal T levels. Normal and high levels of T are accompanied by increased eNOS, nNOS, cGMP, and nitrate/nitrite (NOx) levels, along with reduced PDE5 protein expression.
Conclusion: This study reveals an important role of short-term and modulatory effects of different concentrations of T in HCC. T positively regulates functional activities, inhibition of PDE5 expression, and formation of cGMP and NOx in HCC. These results demonstrate that T indirectly contributes to HCC relaxation via downstream effects on nNOS, eNOS, and cGMP and by inhibiting PDE5. This action provides a rationale for normalizing T levels in hypogonadal men with ED, especially when PDE5 inhibitors are ineffective. T replacement therapy may improve erectile function by modulating endothelial function in hypogonadal men.
INTRODUCTION
Androgens are essential to the development and growth of the penis and regulate erectile function via multiple mechanisms (Traish and Kim, 2005, Traish, et al., 2007). Testosterone (T) regulates central mechanisms of penile erection and influences peripheral neural function. Studies have demonstrated that penile erection in rats is T-dependent (Suzuki, et al., 2007). The nitric oxide synthase/cyclic guanosine monophosphate (NOS/cGMP) pathway is critical for normal erectile function (Burnett, et al., 1992). Androgens regulate NOS levels and modulate phosphodiesterase-5 (PDE5) activity (Traish, et al., 2003, Zhang, et al., 2005). Previous studies show that androgens regulate the expression and the activity of NOS isoforms in the corpus cavernosum (CC) in animal models (Lugg, et al., 1995, Park, et al., 1999, Reilly, et al., 1997, Zvara, et al., 1995).
Clinical studies reveal that in men with ED and low to a low-normal range of T, higher circulating androgen levels improve cavernosal arterial inflow, cavernosal vasodilatation, and the overall erectile response to PDE5 inhibitors (Traish, Munarriz, O'Connell, Choi, Kim, Kim, Huang and Goldstein, 2003). Androgen supplementation has been demonstrated to regulate the activity of PDE5 in castrated animals (Armagan, et al., 2006, Morelli, et al., 2004, Traish, et al., 1999, Zhang, Morelli, Luconi, Vignozzi, Filippi, Marini, Vannelli, Mancina, Forti and Maggi, 2005). Upregulation of NOS by androgens leads to increased nitric oxide (NO) synthesis, which in turn upregulates PDE5 expression and activity (Traish, Goldstein, and Kim, 2007). Androgens have important short- and long-term effects in the regulation of human umbilical artery (HUA) contractility. The short-term effects of T on HUA tone were investigated, and the long-term effects of dihydrotestosterone (DHT) on the expression of various proteins involved in the contractile process are known (Saldanha, et al., 2013). Furthermore, the direct effects of T and its precursor/derivative dehydroepiandrosterone (DHEA) on isolated rat abdominal aortic rings were investigated (Oloyo, et al., 2011). T relaxed the abdominal aorta directly via a non-genomic pathway, which is independent of endothelial-derived vasoactive substances but involves activation of the inward rectifying potassium channel (KIR) and blockade of L-type calcium channels (Oloyo, Sofola, Nair, Harikrishnan and Fernandez, 2011). T induced relaxation of HCC strips by activation of smooth muscle adenosine triphosphate-sensitive K (+) channels. In addition to its known endothelial action, T likely regulates erectile function locally by its action on HCC smooth muscle (Yildiz, et al., 2009).
Mechanistic approaches are needed to understand better the interplay among PDE5 expression, activation of the NO/cGMP pathway, and androgens. This study aimed to compare the enhancing effects of different concentrations of T on NO-dependent and -independent HCC relaxation in organ bath experimentation, and, specifically, targeted the NO/cGMP pathway.
In conclusion, the non-genomic relaxant effects of T on HCC tissues have an auxiliary role to ensure a basal level of perfusion to maintain overall penile function. Our results confirm that T replacement therapy improves erectile function by modulating the cGMP/NO signaling pathway in men with hypogonadism. The potentiation of PDE5 inhibitors with T supplementation may improve erectile function (Frajese and Pozzi, 2005). Future cellular and in vivo studies are warranted to elucidate the clinical significance and to define threshold levels for T replacement in hypogonadal men suffering from ED.
Background: Testosterone (T) deficiency is associated with erectile dysfunction (ED). The relaxant response of T on the corporal smooth muscle through a non-genomic pathway has been reported; however, the in vitro modulating effects of T on human corpus cavernosum (HCC) has not been studied.
Objectives: To compare the effects of various concentrations of T on nitric oxide (NO)-dependent and - independent relaxation in organ bath studies and elucidate its mode of action, specifically targeting the cavernous NO/cyclic guanosine monophosphate (cGMP) pathway.
Materials and Methods: HCC samples were obtained from men undergoing penile prosthesis implantation (n = 9). After phenylephrine (Phe) precontraction, the effects of various relaxant drugs of HCC strips were performed using an organ bath at low (150ng/dL), eugonadal (400ng/dL), and hypergonadal (600ng/dL) T concentrations. The penile tissue measurements of endothelial nitric oxide synthase (eNOS), neuronal (n)NOS, and phosphodiesterase type 5 (PDE5)A were evaluated via immunostaining, Western blot, cGMP, and nitrite/nitrate (NOx) assays.
Results: Relaxation responses to ACh and EFS in isolated HCC strips were significantly increased at all T levels compared with untreated tissues. The sildenafil-induced relaxant response was significantly increased at both eugonadal and hypergonadal T levels. Normal and high levels of T are accompanied by increased eNOS, nNOS, cGMP, and nitrate/nitrite (NOx) levels, along with reduced PDE5 protein expression.
Conclusion: This study reveals an important role of short-term and modulatory effects of different concentrations of T in HCC. T positively regulates functional activities, inhibition of PDE5 expression, and formation of cGMP and NOx in HCC. These results demonstrate that T indirectly contributes to HCC relaxation via downstream effects on nNOS, eNOS, and cGMP and by inhibiting PDE5. This action provides a rationale for normalizing T levels in hypogonadal men with ED, especially when PDE5 inhibitors are ineffective. T replacement therapy may improve erectile function by modulating endothelial function in hypogonadal men.
INTRODUCTION
Androgens are essential to the development and growth of the penis and regulate erectile function via multiple mechanisms (Traish and Kim, 2005, Traish, et al., 2007). Testosterone (T) regulates central mechanisms of penile erection and influences peripheral neural function. Studies have demonstrated that penile erection in rats is T-dependent (Suzuki, et al., 2007). The nitric oxide synthase/cyclic guanosine monophosphate (NOS/cGMP) pathway is critical for normal erectile function (Burnett, et al., 1992). Androgens regulate NOS levels and modulate phosphodiesterase-5 (PDE5) activity (Traish, et al., 2003, Zhang, et al., 2005). Previous studies show that androgens regulate the expression and the activity of NOS isoforms in the corpus cavernosum (CC) in animal models (Lugg, et al., 1995, Park, et al., 1999, Reilly, et al., 1997, Zvara, et al., 1995).
Clinical studies reveal that in men with ED and low to a low-normal range of T, higher circulating androgen levels improve cavernosal arterial inflow, cavernosal vasodilatation, and the overall erectile response to PDE5 inhibitors (Traish, Munarriz, O'Connell, Choi, Kim, Kim, Huang and Goldstein, 2003). Androgen supplementation has been demonstrated to regulate the activity of PDE5 in castrated animals (Armagan, et al., 2006, Morelli, et al., 2004, Traish, et al., 1999, Zhang, Morelli, Luconi, Vignozzi, Filippi, Marini, Vannelli, Mancina, Forti and Maggi, 2005). Upregulation of NOS by androgens leads to increased nitric oxide (NO) synthesis, which in turn upregulates PDE5 expression and activity (Traish, Goldstein, and Kim, 2007). Androgens have important short- and long-term effects in the regulation of human umbilical artery (HUA) contractility. The short-term effects of T on HUA tone were investigated, and the long-term effects of dihydrotestosterone (DHT) on the expression of various proteins involved in the contractile process are known (Saldanha, et al., 2013). Furthermore, the direct effects of T and its precursor/derivative dehydroepiandrosterone (DHEA) on isolated rat abdominal aortic rings were investigated (Oloyo, et al., 2011). T relaxed the abdominal aorta directly via a non-genomic pathway, which is independent of endothelial-derived vasoactive substances but involves activation of the inward rectifying potassium channel (KIR) and blockade of L-type calcium channels (Oloyo, Sofola, Nair, Harikrishnan and Fernandez, 2011). T induced relaxation of HCC strips by activation of smooth muscle adenosine triphosphate-sensitive K (+) channels. In addition to its known endothelial action, T likely regulates erectile function locally by its action on HCC smooth muscle (Yildiz, et al., 2009).
Mechanistic approaches are needed to understand better the interplay among PDE5 expression, activation of the NO/cGMP pathway, and androgens. This study aimed to compare the enhancing effects of different concentrations of T on NO-dependent and -independent HCC relaxation in organ bath experimentation, and, specifically, targeted the NO/cGMP pathway.
In conclusion, the non-genomic relaxant effects of T on HCC tissues have an auxiliary role to ensure a basal level of perfusion to maintain overall penile function. Our results confirm that T replacement therapy improves erectile function by modulating the cGMP/NO signaling pathway in men with hypogonadism. The potentiation of PDE5 inhibitors with T supplementation may improve erectile function (Frajese and Pozzi, 2005). Future cellular and in vivo studies are warranted to elucidate the clinical significance and to define threshold levels for T replacement in hypogonadal men suffering from ED.
