Impotence or, more clinically, erectile dysfunction is the inability to maintain an erection of the penis for satisfactory sexual intercourse regardless of the capability of ejaculation. The recent introduction of effective medication has increased awareness of this previously little appreciated disorder.
Signs and symptoms
Erectile dysfunction is characterised by the inability to maintain erection. Normal erections during sleep and in the early morning suggest a psychogenic cause, while loss of these erections may signify underlying disease, often cardiovascular in origin. Other causes leading to erectile dysfunction are diabetes mellitus (causing neuropathy) or hypogonadism (decreased testosterone levels due to disease affecting the testicles or the pituitary gland).
There are no formal tests to diagnose erectile dysfunction. Some blood tests are generally done to exclude underlying disease.
Penile erection is managed by two different mechanisms. The first one is the reflex erection, which is achieved by directly touching the penile shaft and the second is the psychogenic erection, which is achieved by erotic stimuli. The first one uses the peripheral nerves and the lower parts of the spinal cord, whereas the second one uses the limbic system of the brain. In both conditions an intact neurologic system is required for a successful and complete erection. Stimulation of penile shaft by the nervous system gives rise to the secretion of nitric oxide (NO), which causes the relaxation of smooth muscles of corpora cavernosa (the main erectile tissue of penis), subsequently giving rise to penile erection. Additionally, adequate levels of testosterone (produced by the testes) and an intact pituitary gland are required for the development of a healthy male erectile system. As can be understood from the mechanisms of a normal erection, impotence may develop due to hormonal deficiency, disorders of the neurologic system, lack of adequate penile blood supply or psychological problems.
A few causes of impotence may be iatrogenic (medically caused). Various medications intended to control blood pressure or to modify central nervous system response, may inhibit erection by denying blood supply or by altering nerve activity. Surgical intervention for a number of different conditions may remove anatomical structures necessary to erection, damage nerves, or impair blood supply.
One clinician, and a web site devoted to the practice, maintain that men who masturbate in the prone (face-down) position are more likely to suffer from erectile dysfunction when they attempt intercourse. They call this Traumatic masturbatory syndrome.
Treatment depends on the cause. Testosterone supplements may be used for cases with hormonal deficiency. However, usually the cause is lack of adequate penile blood supply as a result of age-dependent damage of inner walls of blood vessels. Previously, medical substances (e.g. apomorphine ) were used to be directly injected into the erectile tissue of penile shaft to treat impotence. In some cases refractory to the medical treatment, a penile implant (penile prosthesis) could be advised. After the discovery of orally active agents that increase the efficacy of NO, which dilates the blood vessels of corpora cavernosa, more conservative methods were started to be used.
Sildenafil citrate (Viagra®) is an oral agent that blocks specific phosphodiesterases. NO acts on blood vessels by increasing the levels of cyclic guanosine monophosphate, which is required for dilation of the vessels. Phosphodiesterases block this substance and reduce the effect of NO on erectile tissue. By using sildenafil, NO's effects are increased and a more sustained penile erection can be achieved. Other agents with less side effects and holding promise as an effective oral treatment for penile erectile dysfunction are currently being developed. Two newer drugs now available for the treatment of erectile dysfunction are tadalafil (Cialis®) and vardenafil (Levitra®). These agents have a similar mode of action to Sildenafil.
The new drug PT-141 is not acting on the vascular system like the former compounds but increases sexual desire and drive in male as well as female. It is apllied as a nasal spray PT-141 and works by activation of melanocortin receptors in the brain.