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Alprostadil is injected into the side of penis with a very fine needle. It's of great value to have the first shot in the doctor's office before doing this on your own. Self-injection lessons should be given in your doctor's office by an experienced professional. The success rate for getting an erection firm enough to have sex is as high as 85% with this treatment. Many men who do not respond to oral PDE5 inhibitors can be ‘rescued' with ICI.
It is important to understand that ED is frequently, if not usually, directly related to endothelial dysfunction, and that the release of NO by the vasculature of the penile arteries is directly related to the function of intact, healthy endothelium. In the face of endothelial dysfunction, the process of erection fails to occur in a normal fashion.16
Physical causes may include the narrowing of the blood vessels caused by hypertension (high blood pressure), nutritional deficiencies, certain prescription treatments and medications for enlarged prostate or prostate cancer, excess drinking, obesity, heavy smoking, kidney issues, thyroid problems, hormonal changes due to aging, injury, or surgery, diabetes, and high cholesterol levels.
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. 
As men age they require more stimulation up front to get and maintain an erection firm enough for sex. Engaging in some foreplay either on you or on your partner is a great way to get your arousal levels up and get an erection that is firm enough for sex. Many men begin to rush the process of sex once they experience ED. They worry that they will lose their erection so they rush rather than go slow understanding that rushing will only make the problem worse.
Pay attention to your vascular health. High blood pressure, high blood sugar, high cholesterol, and high triglycerides can all damage arteries in the heart (causing heart attack), in the brain (causing stroke), and leading to the penis (causing ED). An expanding waistline also contributes. Check with your doctor to find out whether your vascular system — and thus your heart, brain, and penis — is in good shape or needs a tune-up through lifestyle changes and, if necessary, medications.
Obesity and metabolic syndrome can cause changes in blood pressure, body composition, and cholesterol which may lead to ED. Other conditions that may contribute to erectile dysfunction include Parkinson’s, multiple sclerosis, Peyronie’s disease, sleep disorders, alcoholism, and drug abuse. Taking certain medications can also increase your risk for ED.
Commercials for drugs to improve “low T,” or testosterone, the male hormone, are now vying for airtime, but they address desire, not performance. "Male hormone is not an approved treatment for erectile dysfunction," notes Bennett. "It may be used to increase desire in men who have low testosterone, but it doesn’t improve blood flow to an erection." A doctor can do a blood test to check you for low testosterone, but it is a rare cause of ED. Hormone therapy with injections, patches, or gels applied to the skin may improve mood and sex drive, but it likely won’t fix any mechanical issues. Also, testosterone drugs should not be used by men with prostate cancer. Side effects include acne, breast enlargement, prostate enlargement, and fluid retention.
The sympathetic pathway originates from the 11th thoracic to the 2nd lumbar spinal segments and goes via the white rami to enter the sympathetic chain ganglia. Subsequently nerves travel through the lumbar splanchnic to inferior mesenteric and superior hypogastric nerves to the pelvic plexus. The T10 through T12 segments are most often the origin of sympathetic fibers, and the sympathetic chain ganglia that innervate the penis are located in the sacral and caudal ganglia (3).