"Just because there is evidence doesn't mean it's good evidence," says Andrew McCullough, MD, associate professor of clinical urology at New York University Langone Medical Center in New York City, and one of the original clinical investigators for the ED drug Viagra (sildenafil). "And before men with ED start down the naturopathic route, it's smart to make sure that there isn't some underlying medical condition that needs to be corrected." Moreover, it is estimated that 30 million American men have erectile dysfunction, and 70% of cases are a result of a potentially deadly condition like atherosclerosis, kidney disease, vascular disease, neurological disease, or diabetes. Additionally, ED can also be caused by certain medications, surgical injury, and psychological problems.
Penile erection is largely a vascular process, and the penile endothelium and smooth muscle tissue are very sensitive to functional and structural changes. Vasculogenic ED results from an impairment of endothelial dependent or independent smooth muscle relaxation (functional vascular ED, initial stages), occlusion of the cavernosal arteries by atherosclerosis (structural vascular ED, late stages), or a combination of these.3 Current data support a complex interplay between endothelial dysfunction, subclinical inflammation, and androgen deficiency (Figure 1). The relationship between ED and CAD at the clinical level is supported by this common pathophysiological basis. The ‘artery size’ hypothesis explains why patients with CAD frequently report ED before CAD detection.10 According to this hypothesis, for a given atherosclerotic burden, the smaller penile arteries suffer obstruction earlier than the larger coronary arteries (Figure 2). The same concept holds also true in the case of non-obstructing atherosclerosis: since the smaller penile artery have a greater endothelial surface and erection requires a large degree of vasodilation to occur when compared with arteries in other organs, the same degree of endothelial dysfunction will be symptomatic in these smaller vessels but subclinical in the larger ones (i.e. coronaries). In the same context, accelerated arterial ageing (as indicated by increased arterial stiffening that also affects large arteries of ED patients) may be a common background.11,12 Erectile dysfunction is associated with an incremental inflammatory and endothelial-pro-thrombotic activation.13 Interestingly, this activation is equal to that found in CAD patients with no ED, while when these two conditions are combined the burden is additive. Androgen deficiency may be also implicated in the common pathogenetic pathways of ED and CVD; however, this warrants further substantiation.2
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A deficiency of L-arginine, however, does not generally disrupt nitric oxide synthesis because L-arginine availability is not the rate-limiting step in this process. In fact, research over the past five years has identified an endogenous (occurs in the body naturally) inhibitor called “asymmetric dimethylarginine” or ADMA, an amino acid which blocks the production of nitric oxide. By acting as an L-arginine mimic, this damaging look-alike effectively elbows out L-arginine and pushes it off to the side in the biochemical pathway leading to the synthesis of nitric oxide. ADMA is relatively elevated in patients with hypertension, high levels of cholesterol, triglycerides, homocysteine and low-density lipoprotein (LDL), and low levels of high-density lipoprotein (HDL), as well as with aging itself. This inhibitor of nitric oxide synthesis may very well be the common factor shared by all of these abnormal conditions. Increased levels of this detrimental inhibitor (ADMA) block nitric oxide production, leading to endothelial dysfunction.
Intraurethral alprostadil (Muse) provides a less invasive alternative to intrapenile injection. It is a pellet that is inserted 5–10 min before intercourse, and its effects last for 1 h. The response rate is ∼50–60%. It can be used twice daily but is not recommended for use with pregnant partners. Complications of priapism and penile fibrosis are less common than after alprostadil given by penile injection. The cost is ∼$18–24 per treatment.
The discovery in 1992 of the second messenger of cavernosal smooth muscle relaxation was the critical step that led to the era of nonhormonal oral drug therapy for ED. In 1998, the multicenter trial of sildenafil in the treatment of ED was published in the New England Journal of Medicine, and the era of the phosphodiesterase type 5 (PDE-5) inhibitor began.1 For 5 years, sildenafil was the primary therapy for men with EDDM. Recently, 2 new PDE-5 inhibitors, vardenafil and tadalafil, were introduced.
For oral erectile dysfunction medicines to work as desired, they must be used properly in the first place. This means taking the medicine 30–45 minutes before engaging in sexual intimacy; taking the drug on an empty stomach or at least avoiding a heavy or high-fat meal before taking the drug (this is especially important when using sildenafil); and engaging in adequate genital stimulation before attempting intercourse. Drinking small amounts of alcohol (one to two drinks) should not compromise the effectiveness of erectile dysfunction medicines, but larger amounts of alcohol can diminish a man’s ability to have an erection.