In Italy a man suffered a heart attack because his wife had mixed two Viagra® tablets in his wine. Although he could be saved, another man in Rome was not so lucky: he died from coronary failure due to an overdose of Viagra®. These are just two cases from January 2007 that make it clear that more and more people misuse this medication - arguably the best known of our time - without the knowledge of the risks entailed in usage. And currently the trend is increasing especially with young men to obtain Viagra® without a prescription or consulting a doctor.
The testing of the active pharmaceutical sildenafilcitrate was a disappointment: it did not provide the wanted affect, and thus the study was ended. It was conspicuous, however, that the test subjects did not return their now unneeded pill bottles. Through further investigations, it was quickly discovered that sildenafilcitrate worked as an erection intensifier in men: Viagra® was born, which, through a revolutionary mechanism, works against the psychological and physical effects of erectile dysfunction. It is estimated that 5 million German men and approximately 140 million men world-wide suffer from this condition.
It sounds absurd at first: an erection is caused by a relaxation of the muscles; more exactly, by the relaxation of the blood vessels found in smooth muscle, which, unlike skeletal muscle, cannot be contracted consciously. The arteries of the smooth muscle of a flaccid penis are contracted so that blood is restricted from flowing into the spongy tissue. Many muscle relaxing agents are indeed known, but a selective effect on the smooth muscle of the penis is desired. Physician Dr. Giles Brindley presented in 1983 to a congress of urologists, through personal erectile research and testing, the proof of the success of the direct injection of the normally non selective phentolamine by dropping his pants on stage.
In contrast, Viagra® can be taken orally and still works specifically towards an erection; more exactly stated, towards the preservation of an erection. The relaxation of the smooth muscle of the penis must be initiated by a signal from the brain – yes, in actuality that is also needed – therefore, Viagra® does not work without sexual stimulation. The brain signal is brought to arteries via nerve cells, whereby nitrogen monoxide (NO) is released into the underlying blood vessels. Nitrogen monoxide stimulates the enzyme guanylatcyclase, which sends the signal for the production of cyclo-guanosinmonophosphate (cGMP), which, finally, causes the relaxation of smooth muscle: blood is allowed to flow into different areas of tissue, especially that of the spongy tissue of the penis, which causes the production of an erection.
A further enzyme is involved in this mechanism, the so-called Phosphordiesterase (PDE): this decomposes cGMP, whereby the smooth muscle is contracted again, blood is forced to back out of the spongy tissue and the penis looses the erection. Sildenafilcitrate blocks phosphordiesterase, which results in a slowing in the decomposition rate of cGMP, and the erection is sustained. (Click on the picture to the left in order to view an animation).
> > > Part 2: Viagra® - The problematic side
> > > Part 3: Animation of Viagra® mode of action
