Posts Tagged ‘PDE-5’


// October 25th, 2010 // No Comments » // Impotence

A man’s firm and turgid erection persists until he achieves climax and ejaculates. After ejaculation, his erection fades and his penis returns to its limp (flaccid) state. That process, the conversion of the penis from the sexually prepared and erect condition back to its normal resting flaccid state is also under chemical control. Another intrapenile chemical, an enzyme, called phosphodiesterase 5 (PDE-5) determines whether an erection will stand or collapse.

Enzymes work to either activate or inactivate proteins, and in this case, what is inactivated by PDE-5 is cGMP, the chemical that helped the penis remain erect. As levels of intrapenile cyclic GMP levels fall, so does a man’s erection.

Sildenafil (Viagra) inhibits PDE-5 and allows a man’s cGMP levels to remain elevated. When cGMP levels remain high, a man’s erection persists.

This is good news for men who suffer from impotence or erectile dysfunction.

As long as Viagra helps maintain high intrapenile cGMP levels, a man’s erectile vigor is sustained. With Viagra treatment, between 65 percent and 80 percent of impotent men are able to acquire and maintain erections satisfactory for sexual intercourse.

Male Sexual Chemistry
Body Chemical Does What?
Nitric Oxide Synthase (NOS) Releases Nitric Oxide (NO)
Nitric Oxide Starts blood flowing into penis causing
swelling (tumescence)
Cyclic GMP (cGMP) Increases blood flow so that penis
becomes firm and rigid
Phophodiesterase 5 (PDE-5) Metabolizes cGMP causing loss of erection
Sildenafil (Viagra) Inhibits PDE-5 allowing cGMP levels and
a man’s erection to be sustained


// October 25th, 2010 // No Comments » // Impotence

The development of a “potency pill” that is a medication that could actually make it easier for men to have sex was sheer fantasy until scientists stumbled on sildenafil (Viagra). Originally called UK-92480, then given the generic name sildenafil and more recently the brand name Viagra, this new medication was widely heralded as the pill that could cure impotence.

Sildenafil (Viagra) was originally developed as a blood-pressure-lowering (antihypertensive) medication. Early studies designed to evaluate exactly how effectively sildenafil lowered blood pressure revealed remarkable and unexpected side effects. 1 Hypertensive men taking sildenafil started to experience a surprising number of frequent firm erections.


Viagra, unlike yohimbine, does not purport to be an aphrodisiac, something that can mysteriously heighten a man’s sexual desire. Rather, Viagra has been specifically designed to improve the vigor of a man’s erection. It does this by bolstering a man’s own natural sexual chemistry to make it easier for his penis to acquire and maintain a firm erection during sex.

To date, we know the following about this medication. Viagra speeds up the rate at which blood flows into the penile erectile bodies, the corpora cavernosae. To understand exactly how Viagra works, you have to know a little about what is rapidly emerging as the new science of male sexual chemistry.


The names of the chemicals involved in male sexual chemistry are not particularly erotic, but they are the driving force of men’s sexuality. The interaction of these chemicals is not really that complicated once you know the names of the players.

1. NOS stands for nitric oxide synthase, the enzyme that releases NO (nitric oxide) into the penis.
2. NO starts blood flowing into the penile erectile chambers to start penile swelling, or tumescence.
3. cGMP (short for cyclic GMP) accelerates penile blood flow, resulting in penile rigidity.
4. PDE-5 (phosphodiesterase-5) inactivates cGMP, causing both cGMP levels and a man’s erection to dwindle.
5. Sildenafil (Viagra) blocks PDE-5 and helps maintain cGMP stability as well as the vigor of a man’s erection

Here’s how it all works.

During sexual excitement, a man’s own natural body chemicals diffuse or are transmitted into his penis to trigger the release of nitric oxide (NO). Blood starts to flow into the penile erectile chambers so that the penis plumps up. This is known as tumescence. But the penis is still not ready for sex. The swollen or tumescent penis must be taken to the next plateau, penile rigidity.

Penile rigidity requires a second locally generated chemical called cyclic GMP (cGMP). It is the presence of cGMP that maintains the furious onrush of blood needed for a man’s penis to be converted from tumescent to rigid.

As cGMP takes center stage and even more blood flows into the penis, the pent-up pressure caused by accelerated penile blood flow is so intense that the penis looks like a stuffed sausage straining at its casing. As blood pressure within the penis mounts, the tiny draining emissary veins are choked off so that no blood can leave the penis.

A man’s sexual capability is therefore dependent on a chemical chain reaction beginning with the enzyme NOS, followed by NO, and finally culminating in cGMP to activate the blood flow needed for him to get an erection. The system can break down at any point.

Men who have a substandard quotient of the enzyme NOS within their penile tissue cannot make enough NO to initiate the full and unfettered flow of blood into the penile erectile chambers and as a consequence have difficulty developing a full erection. Lower than normal NOS levels are found in men who are heavy cigarette smokers and in those who have diabetes mellitus or low testosterone levels. This explains, in part, why impotence is so common among long-term smokers, diabetic men, and men with testosterone deficiency.