Cavallini, G., Modenini, F., Vitali, G., & Koverech, A. (2005, November). Acetyl-L-carnitine plus propionyl-L-carnitine improve efficacy of sildenafil in treatment of erectile dysfunction after bilateral nerve-sparing radical retropubic prostatectomy. Urology, 66(5), 1080-5. Retrieved from http://www.sciencedirect.com/science/article/pii/S0090429505006515
The nerves and endothelium of sinusoids and vessels in the penis produce and release transmitters and modulators that control the contractile state of corporal smooth muscles. Although the membrane receptors play an important role, downstream signaling pathways are also important. The RhoA–Rho kinase pathway is involved in the regulation of cavernosal smooth muscle contraction. 
However, studies have shown that fewer then 50% of men with ED and Diabetes respond to oral medicines. Also,fewer than 35% of men with ED after prostate cancer surgery respond to oral medicines. For these men the Internal Penile Implant is currently the best option. The Penile Implant is an approved medical option that has been used for over 30 years. During the course of a 45-minute outpatient procedure, the pump is inserted through a small one-inch opening in the scrotal sac. By squeezing the pump, fluid is pumped, resulting in a long lasting erection. Once inserted, there is no maintenance required for the pump and can remain in place for a lifetime.
According to whom? What's the source of your statistic? Because it sounds astonishingly high, for me to get erections and then lose them. If what you are talking about is men not being able to get erections, why don't you be honest and say that normally this is completely associated with age (say, over-60, and especially over 75), and that the Viagra-class of medications is the simplest and easiest response.
Because the burning side effect is triggered by alprostadil, the formulations with the least alprostadil — tri-mix and certain versions of bi-mix — could work for men who experience burning with the single-drug formula. But some men might choose alprostadil alone because the multi-drug cocktails can cost more and must be dispensed by a compounding pharmacy — one that is authorized to mix medications on site — which could mean the added hassle of a long drive to pick up the drug.
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The dorsal artery provides for engorgement of the glans during erection, whereas the bulbourethral artery supplies the bulb and the corpus spongiosum. The cavernous artery effects tumescence of the corpus cavernosum and thus is principally responsible for erection. The cavernous artery gives off many helicine arteries, which supply the trabecular erectile tissue and the sinusoids. These helicine arteries are contracted and tortuous in the flaccid state and become dilated and straight during erection. 
With drug therapy, there’s a risk of side effects such as headaches, back pain or an upset stomach. Before taking any medication for erectile dysfunction it is important to ensure your doctor is ok with that decision. Medication may not work for all men, for instance, if you have diabetes or have previously had prostate surgery. ED medication might also have serious risks if you’re currently taking nitrates (commonly prescribed for chest pain), have heart disease or have low blood pressure.22
The prostaglandin E1 is contained in a small suppository located at the tip of an applicator. You should urinate first as this lubricates the urethra and makes it easier to insert the applicator into the tip of the urethra (urethral meatus, the opening at the tip of the penis that urine passes through). A patient can release the suppository into urethra by gently wiggling the applicator and pressing the button at the end. Rubbing the penis allows the suppository to dissolve, and the prostaglandin is absorbed through the tissue of the urethra into the penis. It takes 15 to 30 minutes for this occur. Once into the penis, the prostaglandin causes increased blood flow into the penis. The prostaglandin can be present in the ejaculate, and thus doctors recommend that men use a condom when having intercourse with a pregnant partner. Men may need to use a condom if vaginal irritation occurs in female partner.
Since endothelial dysfunction, CVD and ED are closely associated in epidemiological studies, the question for clinicians is whether to recommend the man presenting with ED undergo a cardiovascular (CV) evaluation. Clearly, based on numerous studies, ED can be considered at least a ‘marker’ for possible further vascular disease or CVD.15 In their report, Vlachopoulos and coworkers make the point that the man presenting with ED, the clinician, is offered an opportunity to attempt to improve the health of the man by addressing lifestyle modification, and consider further vascular evaluation owing to the clear relationship between endothelial dysfunction, ED and CVD.19
Knowing about your history of ED will help your health provider learn if your problems are because of your desire for sex, erection function, ejaculation, or orgasm (climax). Some of these questions may seem private or even embarrassing. However, be assured that your doctor is a professional and your honest answers will help find the cause and best treatment for you.