Enhancement of the RhoA/Rho kinase pathway is associated with stress‐related erectile dysfunction in a restraint water immersion stress model

Stress is a risk factor for erectile dysfunction (ED); however, the pathology of stress‐induced ED remains unclear. Accordingly, in this study, we investigated the mechanisms of stress‐induced ED using a rat model. Ten‐week‐old male Wistar/ST rats were maintained in a cage filled with water to a height of 2 cm (stress group) or a normal cage (control group). We found that water immersion stress significantly enhanced the contractile response to noradrenaline in the corpus cavernosum (CC) (p < 0.05). Moreover, stress significantly decreased erectile function, as assessed by changes in intracavernous pressure (p < 0.01). In addition, Rho kinase‐1 (ROCK‐1) protein expression was significantly upregulated under stress conditions (p < 0.05), and phosphorylated myosin light chain (phospho‐MLC) levels, contribute to smooth muscle contraction, were also upregulated (p < 0.01). Treatment with fasudil hydrochloride, a Rho kinase inhibitor, for 5 days significantly improved erectile function (p < 0.01) and normalized ROCK‐1 and phospho‐MLC levels (p < 0.01). Thus, the RhoA/Rho kinase pathway may be associated with stress‐induced ED via contraction of CC. Stress also decreased the smooth muscle/collagen ratio of CC (p < 0.01), and fasudil treatment did not alleviate these effects (p = 0.50). These findings suggested that penile fibrosis gradually progressed under stress conditions and that fibrosis may be independent of the RhoA/Rho kinase pathway, implying that longer exposure to stress may promote ED. We conclude that stress‐induced ED was caused by contraction of CC mediated by the RhoA/Rho kinase pathway.