Low androgen level impairs erectile function of rat by regulating the Ng/CaN/AKT/eNOS pathway in penile corpus cavernosum

Background The mechanism by which low androgen status inhibit erectile function has not yet been clearly elucidated. Neurogranin (Ng) is a Ca2+-sensitive calmodulin binding protein that is expressed in endothelial cells and regulates eNOS function. Objectives To investigate whether low androgen status inhibit erectile function by regulating the Ng/CaN/AKT/eNOS pathway in the penile cavernous tissue of rats. Materials and methods Thirty-six 8-week-old male Sprague-Dawley rats were randomly divided into six groups as follows (n = 6): 4-week control group (4w-control), 4-week castration group (4w-cast), 4-week castration+testosterone replacement group (4w-cast+T), 8-week control group (8w-control), 8-week castration group (8w-cast), and 8-week castration+testosterone replacement group (8w-cast+T). Four weeks and eight weeks after surgery, the ratio of the maximum intracavernous pressure/mean arterial pressure (ICPmax/MAP) was examined. The level of NO and the expression of Ng, calcineurin (CaN), AKT, p-AKT(S473), eNOS, and p-eNOS(Ser1177) in the penile cavernous tissue of each group were determined. Results Ng and CaN were mainly expressed in the membrane and cytoplasm of endothelial cells and smooth muscle cells in the penile cavernous tissue of rats. The ICPmax/MAP and the concentration of NO in the cast group were significantly lower than those in the control group and cast+T replacement group (p < 0.01). The expression of Ng and the ratios of p-AKT/AKT and p-eNOS/eNOS in the penile cavernous tissue of rats in the cast group were significantly lower than those in the control group and cast+T replacement group (p < 0.01). The expression of CaN in the penile cavernous tissue of rats in the cast group was significantly increased compared with that in the control group and the cast+T replacement group (p < 0.01). Conclusion Inhibiting the expression of Ng and subsequently upregulating the expression of CaN in the rat penile cavernous tissue was one of the upstream mechanisms of low androgen status inhibiting erectile function by inhibiting the AKT/eNOS signaling pathway.