What causes ED?
The natural process of sexual stimulation activates a series of biochemical reactions that relaxes blood vessels in the penis and allows blood flow into the corpus cavernosum, which is the spongy erectile tissue of the penis that fills with blood causing an erection. Loss of an erection is due to the activity of an enzyme called phosphodiesterase type 5 (PDE5) that breaks down the chemical responsible for relaxing blood vessels, cyclic guanosine monophosphate (cGMP), which results in contraction of the blood vessels, preventing blood flow. If the natural processes do not function properly due to physical or psychological problems, this can lead to erectile dysfunction or ED.
Medications for ED
The medications available for treating ED are used to increase blood flow into the penis, working by different mechanisms. These are:
- Phosphodiesterase type 5 (PDE5) inhibitors
- Prostaglandins
Phosphodiesterase type 5 (PDE5) inhibitors
Phosphodiesterase type 5 (PDE5) inhibitors block the action of the enzyme PDE5 that prevents blood flow into the penis and this action allows blood to remain in the penis, which maintains an erection. This resolves ED by allowing the natural process of sexual stimulation to activate the mechanism for achieving and maintaining an erection. However, PDE5 inhibitors only work when sexually aroused and do not work otherwise; their effect lasts for around four hours. These medications include sildenafil, tadalafil, vardenafil.
Prostaglandins
Prostaglandin E1, also known as alprostadil, is a naturally occurring chemical that has many functions including relaxation of smooth muscle in various tissues, including the corpus cavernosum and blood vessel walls. Prostaglandin E1 is used to treat ED by direct injection into the penis resulting in widening of the cavernosal arteries in the penis and relaxation of trabecular smooth muscle in the penis. This increases blood flow into the penis causing an erection.