Sexual Chemistry - questions and answers
What is erectile dysfunction?
Erectile dysfunction, or impotence, is defined by the National Institute of Health as: "the persistent or recurrent inability to attain or maintain an erection sufficient for sexual intercourse." Erectile dysfunction is a common problem which is thought to affect at least one in ten men over the age of 21 - that's an estimated 2.3m men in the UK alone.
Until about 20 years ago, erectile dysfunction was considered to be a purely psychological problem, but research now suggests that physical problems are present in about 75% of sufferers. However, the majority of men with erectile dysfunction experience a combination of psychological and physical causes, ranging from diseases like diabetes, kidney failure and high cholesterol, to stress, anxiety and depression.
What is female sexual dysfunction?
A recent article in the BMJ has sparked significant debate over whether female sexual dysfunction actually exists. What is clear is that it isn't a single problem with a single cure, but an umbrella term which covers an entire range of sexual problems experienced by women.
Inhibited sexual desire is thought to be the most common problem and is thought to affect 80% of women who seek help. The term female sexual dysfunction also covers other difficulties including pain during intercourse, arousal problems and lack of lubrication, an inability to achieve orgasm, and vaginismus (an involuntary spasm of the muscles surrounding the vaginal entrance making penetration impossible).
As with men, there are many factors that can contribute to these problems, some of which may be psychological and some physical (including medical conditions such as, diabetes, cardiovascular disease, multiple sclerosis, hormonal changes and certain prescription drugs).
How does Viagra work?
Viagra works by increasing the blood flow to the penis. To cause an erection the brain sends signals via the spinal cord and pelvic nerves to the penis. A chemical messenger called nitric oxide is then released by nerve endings in the penis. This nitric oxide gas causes the production of another chemical messenger, cyclic GMP, which in turn expands the surrounding blood vessels and so increases the blood entering the penis, causing an erection. In impotent men the erectile tissue doesn't get enough cyclic GMP.
Levels of cyclic GMP in the penis are controlled by an enzyme called PDE-5 which acts as an off switch by breaking down cyclic GMP. Viagra blocks this enzyme. By preventing cyclic GMP from being destroyed, its levels are increased and an erection can be established and maintained.
What other treatments are available for erection problems?
Viagra was the first oral treatment for erection problems and since its launch in 1998 has been used to treat more than 20m men worldwide. There are a whole range of other treatments available from vacuum pumps to surgical intervention.
In 2001 apomorphine was licensed under the trade names Uprima and Ixense, and was the only other oral treatment for erectile dysfunction. Two new rival drugs both work in a similar way to Viagra. Cialis was launched on 4 February 2003 by Eli Lilly. GlaxoSmithKline's drug Levitra is also due to be launch in 2003.
How does apomorphine work?
Unlike Viagra, which acts on the penis, apomorphine has its effect in the brain. Individual nerve cells in the brain and nervous system communicate with one another using chemical messengers called neurotransmitters. Apomorphine mimics the action of one of the brain's main neurotransmitters, dopamine, and is thought to act primarily on an area of the brain called the hypothalamus. Areas of the hypothalamus are thought to control the more reflexive side of our sexual response including vaginal blood flow in women and erection in men. By mimicking the action of dopamine in the hypothalamus, apomorphine strengthens the signals the brain sends to the penis to cause an erection.
Does apomorphine affect desire?
The clinical trials that lead to apomorphine's approval for erectile dysfunction showed no increase in libido or sexual desire. The evidence for an increase in sexual interest in men is at present only anecdotal and more research is needed to confirm this finding.
However, since dopamine acts as a neurotransmitter in many areas of the brain, apomorphine's effects are not limited to the hypothalamus. Dopamine is also an important neurotransmitter in the limbic system, the part of the brain thought to control emotion. Those who believe apomorphine can effect desire postulate that this could be due to the drug being active in these areas.
Will apomorphine be available for women soon?
No. At present there has only been one very small pilot study looking into the use of apomorphine for the treatment of women suffering from loss of desire. While the results of this study were encouraging, much larger and more tightly controlled clinical trials will need to be done to really show whether apomorphine is an effective treatment. One such trial is already underway in Scotland, involving over 300 women, but even if the results of this are positive the drug is still several years away from being licensed for women.
Are other brain drugs being developed?
One of the other drugs known to be in development is called Pt-141. In female rats it has been shown to have a very specific effect increasing sexual desire. The drug is currently in human clinical trials for both men and women.