Mechanistic link between erectile dysfunction and systemic endothelial dysfunction in type 2 diabetic rats.

Men with type 2 diabetes mellitus (T2DM) and erectile dysfunction (ED) have greater risk of cardiovascular events than T2DM men without ED, suggesting ED as a predictor of cardiovascular events in diabetic men. However, molecular mechanisms underlying endothelial dysfunction in the diabetic penis explaining these clinical observations are not known. We evaluated whether the temporal relationship between ED and endothelial dysfunction in the systemic vasculature in T2DM involves earlier redox imbalance and endothelial nitric oxidase synthase (eNOS) dysfunction in the penis than in the systemic vasculature, such as the carotid artery. Rats were rendered T2DM by high-fat diet for 2 weeks, followed by an injection with low-dose streptozotocin. After 3 weeks, erectile function (intracavernosal pressure) was measured and penes and carotid arteries were collected for molecular analyses of eNOS uncoupling, protein S-glutathionylation, oxidative stress (4-hydroxy-2-nonenal, 4-HNE), protein expression of NADPH oxidase subunit gp91(phox) , endothelium-dependent vasodilation in the carotid artery, and non-adrenergic, non-cholinergic (NANC)-mediated cavernosal relaxation. Erectile response to electrical stimulation of the cavernous nerve and NANC-mediated cavernosal relaxation was decreased (p < 0.05), while relaxation of the carotid artery to acetylcholine was not impaired in T2DM rats. eNOS monomerization, protein expressions of 4-HNE and gp91(phox) , and protein S-glutathionylation, were increased (p < 0.05) in the penis, but not in the carotid artery, of T2DM compared to non-diabetic rats. In conclusion, redox imbalance, increased oxidative stress by NADPH oxidase, and eNOS uncoupling, occur early in T2DM in the penis, but not in the carotid artery. These molecular changes contribute to T2DM ED, while vascular function in the systemic vasculature remains preserved.

eNOS-uncoupling in age-related erectile dysfunction.

Aging is associated with ED. Although age-related ED is attributed largely to increased oxidative stress and endothelial dysfunction in the penis, the molecular mechanisms underlying this effect are not fully defined. We evaluated whether endothelial nitric oxide synthase (eNOS) uncoupling in the aged rat penis is a contributing mechanism. Correlatively, we evaluated the effect of replacement with eNOS cofactor tetrahydrobiopterin (BH(4)) on erectile function in the aged rats. Male Fischer 344 'young' (4-month-old) and 'aged' (19-month-old) rats were treated with a BH(4) precursor sepiapterin (10 mg/kg intraperitoneally) or vehicle for 4 days. After 1-day washout, erectile function was assessed in response to electrical stimulation of the cavernous nerve. Endothelial dysfunction (eNOS uncoupling) and oxidative stress (thiobarbituric acid reactive substances, TBARS) were measured by conducting western blot in penes samples. Erectile response was significantly reduced in aged rats, whereas eNOS uncoupling and TBARS production were significantly increased in the aged rat penis compared with young rats. Sepiapterin significantly improved erectile response in aged rats and prevented increase in TBARS production, but did not affect eNOS uncoupling in the penis of aged rats. These findings suggest that aging induces eNOS uncoupling in the penis, resulting in increased oxidative stress and ED.