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21.09.2009


High dose of sildenafil raises testosterone twelve-fold in animal study

Doctors who prescribe the erection medicine Viagra active ingredient sildenafil [structural formula shown below] should bear in mind that sildenafil can raise testosterone levels in men. And not just a little. Brazilian scientists at the Fiocruz research institute base this conclusion on tests they did on mice. The testosterone level of the animals rose by a factor of at least twelve when they were given sildenafil.

Sildenafil


High dose of sildenafil raises testosterone twelve-fold in animal study

The theory that sildenafil stimulates the production of testosterone by the Leydig cells in the testes is not completely new. It is based on what we know about how the Leydig cells work and what we know about sildenafil.

Sildenafil sabotages the enzyme phosphodiesterase type 5 in the body. This enzyme usually breaks down the second messenger cGMP a little brother of cAMP into an inactive protein. More cGMP means wider blood vessels and more powerful erections. Because cGMP also helps to transmit signals from hormones that attach themselves to receptors on the cell membrane, more cGMP may also mean that Leydig cells listen better to messenger hormones like LH. Ergo: sildenafil could lead to higher testosterone levels.

In theory.

To test the theory the Brazilians gave mice drinking water to which sildenafil had been added for a period of four weeks. The lab animals consumed 25 mg of sildenafil per kg bodyweight each day. The human equivalent of that dose would be approximately 300 mg sildenafil daily. That's not an advisable dose for humans. The table below shows that sildenafil increased the testosterone concentration in the animals' blood twelve-fold.


High dose of sildenafil raises testosterone twelve-fold in animal study


When the Brazilians examined the mice's Leydig cells, they found that the cells contained more steroidogenic acute regulatory protein (StAR-protein). This protein helps in the biosynthesis of testosterone.


High dose of sildenafil raises testosterone twelve-fold in animal study


The concentration of the cytochrome P450 side-chain cleavage enzyme was also higher. This enzyme cuts side-chains off cholesterol, thus enabling Leydig cells to convert cholesterol into testosterone.


High dose of sildenafil raises testosterone twelve-fold in animal study


Italian researchers have discovered mild hormonal effects in men using erection medicines. Medical doses of sildenafil lead to a slightly increased production of testosterone and a slightly reduced level of estradiol. This effect is of a totally different order much more modest than that recorded in the animal study.

Source:
Int J Exp Pathol. 2009 Aug;90(4):454-62.