The mechanisms by which testosterone plays a role in erectile function are not completely understood. A study evaluating the effect of testosterone on erections in surgically castrated rabbits and control animals, in which the rabbits’ intracavernosal pressures were compared after cavernosal nerve stimulation, determined that castrated rabbits had much lower pressures after stimulation than control rabbits did.  Notably, the pressures increased when castrated rabbits received exogenous testosterone replacement.
Drugs for treating impotence can be taken orally or injected directly into the penis or inserted into the urethra at the tip of the penis. Oral testosterone can reduce impotence in some men with low levels of natural testosterone. Patients also have claimed effectiveness of other oral drugs--including yohimbine hydrochloride, dopamine and serotonin agonists, and trazodone--but no scientific studies have proved the effectiveness of these drugs in relieving impotence. Some observed improvements following their use may be examples of the placebo effect, that is, a change that results simply from the patient's believing that an improvement will occur.
If PDE-5 inhibitors are not suitable or don’t work, other therapies include injections into the base of the penis, which cause flow of blood into the penis and a fairly immediate erection that lasts around an hour. The drugs injected are alprostadil (Caverject and Erectile dysfunctionex) and Invicorp (VIP and phentolamine). Alprostadil may also be inserted as a gel into the opening of the penis. This is not suitable if your partner is pregnant.
Look, ED can have many causes. Most of the time, it’s physiological. But there are also lots of psychological reasons why someone may experience ED. Treating ED isn’t all about medication. Dealing with some of these psychological issues can help you battle ED, too. I’m talking about depression, anxiety, loss of desire, sense of inadequacy, guilt, fatigue, anger, relationship dysfunction. Working through these types of psychological challenges can help you achieve the happy, healthy manhood you deserve.
Monitoring erections that occur during sleep (nocturnal penile tumescence) can help you and your doctor to understand if the erectile dysfunction is due to psychological or physical causes. The nocturnal penile tumescence test is a study to evaluate erections at night. Normally men have three to five erections per eight hours of sleep. The test can be performed at home or in a sleep lab. The most accurate way to perform the test involves a special device that is connected to two rings. The rings are placed around the penis, one at the tip of the penis and the other at the bottom (base) of the penis. The device records how many erections occur, how long they last, and how rigid they are. The test is limited in that it does not assess the ability to penetrate.
Organic impotence refers to the inability to obtain an erection firm enough for vaginal penetration, or the inability to sustain the erection until completion of intercourse. In contrast to psychogenic impotence, which is impotence caused by anxiety, guilt, depression, or conflict around various sexual issues, organic impotence, the more common of the two categories of erectile dysfunction, is caused by physical problems. Ten to 20% of middle-aged men and a much higher percentage of elderly men are impotent. Aside from its importance as a common and distressing sexual problem, organic impotence may herald important medical problems.