Erectile dysfunction (ED) or impotence is the inability to achieve and maintain a full erection during sexual arousal. It affects an estimated 10-20 million men, including 25% of men older than 50. The cause of ED can be primarily organic, psychogenic in nature, or a mixture of the two. In 85% of cases affecting men aged 50 and older, organic factors such as vascular disease and atherosclerosis of the penile artery are the cause.

Physical factors include:

• Systemic diseases (diabetes mellitus, syphilis, alcoholism - abstain for 30 days to see if there is improvement, drug dependency, hypopituitarism, and hypothyroidism, and adrenal insufficiency)
• Local disorders - prostate enlargement (BPH), congenital abnormalities and inflammatory diseases of the genitalia, prostatitis; vascular disturbances such as aortic aneurysm and atherosclerosis (for example Leriche's syndrome)
• Neurogenic disorders - multiple sclerosis, spinal cord lesions, pituitary microadenoma with hyperprolactinemia, and cardiovascular accident; drugs such as hypertensives, sedatives, Proscar (finasteride), tranquilizers, and amphetamines.
• Surgical procedures such as sympathectomy, prostatectomy and castration produce varying effects. Impotence is usually not induced by transurethral prostatectomy, whereas it almost always occurs after perineal prostatectomy.
• Impotence is not inevitable with aging, even into the 70s or 80s. While the amount and force of the ejaculate and thus sexual tension and the need to ejaculate are decreased, the capacity for erection often is retained.
• Contributing causes include a lack of exercise, smoking, excess alcohol consumption, obesity and increased total cholesterol or reduced HDL levels.

Psychological causes
These can include abnormal fears of the vagina, sexual guilt, fear of intimacy, or depression. ED may be situational (involving place, time or a particular partner), some perceived competitive defeat, or damage to self-esteem. Counseling may be required to resolve these issues. Psychological factors are strongly implicated if the patient has situational impotence, night or morning erections, or can achieve a firm erection by stimulation.

Viagra may help men who have been left impotent by prostate disease, diabetes or atherosclerosis, but some doctors are still prescribing it with caution, if at all. First, correct any lifestyle problems: reduce alcohol consumption, get sufficient exercise, watch what you eat, stop smoking, optimize your health, and improve your circulation with ginkgo, if needed. Don't use it with any form of heart disease. If you decide to try Viagra, discuss it with your spouse first and then work with your doctor to find the lowest effective dose. A 50mg tablet may be too little or too much.

Men get erections when sexual thoughts, originating in the brain, initiate a flow of nerve signals, some of which are parasympathetic, down the spinal cord to the arteries and smooth muscle in the penis. The arteries that supply the penis then dilate, and the muscles that control the two rods of sponge - like tissue filling the core of the penis - the corpora cavernosa and the corpus spongiosum - relax. As they relax, they allow the increased flow of blood through the penile arteries to fill the spongy space with blood. The increasing pressure in the penis compresses the veins that drain blood from the penis, preventing outflow. The more blood that fills the penis, the larger and harder the erection will be, because as long as blood is flowing through the arteries, the out flow remains severely restricted. The penis returns to a flaccid state when the penile arteries constrict, relaxing pressure on the veins and allowing the blood to drain out.

All these activities are under the control of NO molecules. The nerves that serve the spongy tissue and the penile arteries are rich in NO, so when you become sexually aroused, the NO rich nerves quickly convert L-arginine to NO. These NO molecules diffuse to nearby arteries and smooth muscle, causing them to dilate and relax. Erection is reversed by contraction of the arteries involved, and that in turn occurs with stimulation by other nerves (sympathetic), either with ejaculation, anxiety or other causes of inhibition.

NO can be activated by a number of common substances released from the nerves. Especially important is the neurotransmitter acetylcholine.

Laboratory analysis of 22 sexual enhancement products available in the United States found nine (41%) were properly labeled, contained the claimed ingredients, and were not spiked with the prescription drug Viagra. [Consumer Labs Report]

Reference:
"Gingko biloba Extract in the Therapy of Erectile Dysfunction," M. Sohn and R. Sikora, Journal of Sex Education Therapy, Vol. 17, 1991, pp.53-61.