The drug Viagra revolutionised the treatment of sexual dysfunction in men on its launch five years ago. An accidental discovery, the tablet that gave impotent men the chance once more to have natural erections became the fastest selling pill in history and has earned its manufacturer, Pfizer, over $6bn.
The search is now on for a similar drug that could help women. Research is revealing that female sexuality is more complex than expected. For women suffering from a loss of desire many scientists believe that drugs acting on the brain may be the way forward. A pioneering Scottish study may have identified just such a drug and begun testing it scientifically.
Part 1: A man thing
An erection is achieved by filling the erectile tissue of the penis with blood. Blood vessels widen to allow blood in and then constrict to maintain the pressure. Male impotence was long thought to be a psychiatric effect, a result of stress, anxiety or depression. Medical advice was that there was not much to be done. Some patients refused to take this message on board.
Geddings Osbon used his profession (working in a tyre workshop in Georgia, USA) as inspiration for one solution. Suffering from impotence himself, he designed a vacuum pump to create an erection by engorging his penis with blood and containing it with a rubber band. Despite its problems of discomfort, his vacuum device achieved popularity and is still recommended by medics to some men with erectile dysfunction.
The next leap forward came in 1983 when British urologist, Giles Brindley, gave an eye-opening presentation to colleagues in the field, gathered at Las Vegas. He told them he had just injected himself with phenoxybenzamine and then showed them the results, by dropping his trousers and displaying his erect organ.
Brindley had proved that a drug could be used to treat erection problems. Modern science accepts that impotence can be the result of a number of medical conditions: high blood pressure, furred arteries and some types of diabetes. Injecting phenoxybenzamine is relatively easy but an instant erection hardly fits into most people's natural sexual practice. A pill would still be ideal.
Part 2: Blues for the boys
In 1985, the drug company Pfizer was working on treatments for the heart complaint, angina. Dr Ian Osterloh and Dr Gill Samuels were using sildenafil citrate to relax blood vessels, in the hope of easing the pain of narrowed cardiac arteries. They were about to become unwitting sexual pioneers. Their drug did significantly increase blood flow, but not in the heart. It did so in the penis.
With its side effect recognised, studies began to assess the compound's ability to treat impotence. Researchers in Bristol assembled a library of explicit films in order to provide a controlled method of arousing the subjects. They thought the blue tablets wouldn't cause an erection on their own, but could help lust to run its natural course.
The investigation pieced together how the compound - Viagra - was beating male impotence. When sexually excited, cells in the penis produce a chemical messenger known as cyclic GMP. Its effect is to allow more blood to enter the erectile tissue, making it more rigid. The level of cyclic GMP is continuously kept in check by an enzyme. Viagra acts to inhibit the enzyme, preserving cyclic GMP and enabling the man to achieve an erection at a time that fits into having sex.
Part 3: Viagra for women
With an understanding of the chemical mechanism that allows Viagra to intervene in the physical process of male erections, it was natural for scientists to wonder what effect the drug would have for women. Female sexual problems were a field that had received far less attention than males'. Like in men, it was supposed to be primarily a psychological complaint.
Research showed that arousal chemicals in men and women are the same and also that the physiological similarities between the penis and clitoris are greater than many realised. However, a number of studies have revealed that for the vast majority of women with sexual problems, Viagra is little help. (Women with pelvic blood flow problems and some spinal injuries can benefit.)
Part 4: More intelligent sex
The reason it seems is that for women, being turned on sexually is more to do with the brain than the pelvis. Dr Ellen Laan turned to erotic videos to try to understand the female sexual response. She showed women two films. One concentrated on the man's pleasure; one on the woman's. Her subjects experienced increased vaginal blood flow with both films, but only reported being turned on by the film that was more focussed on female pleasure. Laan deduced that - unlike men - for women the genitals are not the best indicator of arousal.
The most common complaint of women who seek help for sexual problems is not a physical one but a loss of desire. Using the contraceptive pill or anti-depressants can prompt it, as can childbirth, the menopause or falling out of love. Sometimes it seems there is no reason. Finding a cure is much harder than helping men to bolster their equipment.
Part 5: Sex on the brain
A Scottish nurse could yet become the pioneer for a drug treatment for women. Ian Russell specialises in helping people with sexual problems. In 2001, he started giving a new drug product - apomorphine hydrochloride - to men with impotence.
Apomorphine (licensed for men as Uprima and Ixense) is a drug designed to work in the brain itself. It mimics the brain signalling chemical, dopamine, and has been shown to act in the hypothalamus, an area known to control physical arousal. In men, apomorphine amplifies the signal to have an erection. But Ian Russell's trial participants reported that taking the drug regularly did more than overcome impotence; it raised their levels of desire.
This unexpected discovery made Russell realise the drug could be useful for his female patients as well. He approached Prof Jeremy Heaton from Ontario, Canada, who had developed apomorphine. Jeremy gave him the encouragement he needed to set up a small pilot study. He gave women varying doses of apomorphine for 18 weeks. Questionnaires at six week intervals assessed any change in their sexual function.
Eight out of the ten women reported an increase in sexual desire and in their overall sexual satisfaction. Russell was encouraged but well aware that one small uncontrolled study could yield unrepresentative results. He is now embarking on a larger, double blind study.
Meanwhile, research on rats has shown that dopamine's role in the brain extends beyond the hypothalamus. It's known to play a role in the limbic system, the part of the brain thought to control emotion. This could explain the connection with desire.
Drugs that aim to tackle female sexual problems are still years away from being licensed. However, as the differences - and similarities - between the sexes become clearer, the essence of male and female sexuality is opening up to scientific investigation.
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