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Arginine and Select Phytonutrients Enhance
Libido
by Jim English
A normal sexual response in men and women begins
in the presence of sexually oriented stimulation. When the mood
is right, the body responds by releasing a cascade of chemicals
that direct the flow of blood into the sexual organs. In women,
this leads to engorgement and lubrication of the organs as the body
prepares for intercourse. In men, this rush of blood is directed
into a pair of pockets, known as the corpus cavernosum, that run
inside the shaft of the penis. This inflow of blood is critical
to the enlargement and stiffening of the penis.
This engorgement is triggered by a unique neurotransmitter
called nitric oxide (NO). Nitric oxide, in turn, stimulates the
production of another signaling enzyme called cyclic guanosine monophosphate,
or cGMP for short. Under normal circumstances, cGMP signals the
smooth muscles surrounding the arteries of the penis to relax and
allow blood to flow into the penis. Any condition that interferes
with the signaling of these messenger enzymes can quickly lead to
the breakdown of the entire process and cause impotence.
According to the National Institutes of Health, impotence, or erectile
dysfunction, is defined as the inability to attain or sustain an
erection adequate for satisfactory sexual intercourse. Experts believe
impotence affects between ten and fifteen million American men.
In 1985, the National Ambulatory Medical Care Survey counted 525,000
doctor-office visits for erectile dysfunction, and that number has
greatly increased since then.
Impotence usually has a physical cause, such as
disease, injury, or drug side effects. Any disorder that impairs
blood flow in the penis has the potential to cause impotence. It
occurs as men age: about five percent of men at the age of forty,
and between fifteen and twenty five percent of men at the age of
sixty-five experience impotence. Yet impotence is not an inevitable
part of aging.
In 1998, the FDA approved the prescription drug Viagra (sildenafil
citrate) as a treatment for men suffering from non-organic impotence
due to conditions such as diabetes, radical prostatectomy, spinal
cord injury, and vascular disease. Viagra was originally investigated
as a potential anti-angina medication based on its ability to release
nitric oxide and increase blood flow to the heart. Although Viagra
failed as a heart medication, researchers in London became excited
when men in the clinical trials reported the frequent occurrence
of unaccustomed erections and improved sexual performance.
Following this serendipitous finding (and five
years of clinical trials), Viagra was finally granted approval as
a treatment for men who had difficulty achieving erections because
of conditions such as diabetes, radical prostatectomy, spinal cord
injury, and vascular disease.
Viagra was found to help men achieve and maintain
erections by (1) enhancing the effects of the neurotransmitter nitric
oxide (NO), and (2) maintaining higher levels of the enzyme cGMP,
the two key players in penile erection. Viagra does this by selectively
inhibiting the enzymes that destroy cGMP, leading to elevated cGMP
levels. This, in turn, increases blood flow to the genitals and
leads to stronger erections and intensified sensation.
Viagra was found to help eighty percent of men
suffering from non-organic impotence. Additionally, Viagra also
seems to enhance sexual performance and enjoyment, and reduce the
latent period between erections, even in men who have no dysfunction.
Viagra has also gained a reputation with women,
which makes sense when one considers that the clitoris, which is
structurally similar to the penis, becomes engorged with blood during
sexual arousal. Viagra may provide similar benefits to women, stimulating
the release of NO, encouraging blood flow and enhancing sexual sensation
and orgasm.
While Viagra is effective for millions of men, the side effects
for many —facial flushing, headaches, and indigestion—
are too troublesome for continued enjoyment. And, more seriously,
soon after its introduction, vision problems began to surface in
men taking Viagra, leading to warnings for people with retinal eye
conditions, such as macular degeneration or retinitis pigmentosa,
to use the drug only with caution.
In addition to eye problems, both the FDA and
the manufacturer began to issue warnings against taking Viagra with
any nitrate-based cardiac medications (i.e., sublingual nitroglycerin
tablets, nitroglycerin patches, etc.). Doctors were warned that
heart patients should not be treated with nitroglycerin if the patient
had used Viagra in the previous twenty-four hours. Additionally,
the manufacturer reported several cases where patients who received
both drugs died after developing irreversible hypotension (a severe
drop in blood pressure).
As safety issues with Viagra began to arise, researchers once again
began to seek out safer alternatives for treating impotence. Many
current pharmaceuticals have evolved from the historical search
for herbal compounds to cure or reverse sexual dysfunction. Often,
traditional nostrums rely on purely magical (placebo) effects, such
as the phallic-influenced belief in the effect of rhinoceros horn—which,
in fact, offers no benefit to humans and is fatal for the unfortunate
rhino. Conversely, many plant-based traditional treatments, using
herbs such as damiana, maca, muira puama, tribulus, and yohimbe,
have been explored for their effectiveness in treating sexual dysfunction.
Viagra works to increase both the levels and activity of nitric
oxide, leading to increased cGMP, increased blood flow to the genitals,
and more intense sensations. Fortunately, there is a less expensive
way to naturally increase the amount of nitric oxide released during
sexual stimulation. The key is supplemental L-arginine, the direct
precursor of nitric oxide.
In the 1990s, scientists discovered that L-arginine,
a non-essential amino acid commonly found in the diet, is an oxidative
precursor of nitric oxide (NO). As mentioned previously, nitric
oxide is required for achieving and maintaining penile erection.
Under conditions in which nitric oxide is produced for a specific
physiologic purpose, the concentration of L-arginine (from which
it is formed) can be a limiting factor.
Researchers at New York University School of Medicine
gave L-arginine to a group of impotent men, and found that six out
of 15 men receiving the amino acid claimed an improved ability to
achieve erections, while none of the 15 men in the placebo group
reported any benefit.
L-dopa is a chemical precursor of the neurotransmitter dopamine
(which in turn is a precursor of norepinephrine). In other words,
the body uses L-dopa to make dopamine. Several lines of evidence
link activity of dopamine in the brain with sexual behavior. Generally,
it appears that higher levels of dopamine are associated with more
sexual interest and vice versa. Increased brain dopamine activity
caused by taking the drug L-dopa is believed to be the cause of
a 'hypersexuality' syndrome in people who take the drug for Parkinson’s
disease.
While L-dopa is available only by prescription,
you can increase your brain dopamine levels by taking the natural
herb, Mucuna pruriens, which is a natural source of L-dopa.
The herb Tribulus terrestris has been used since ancient times in
India as a treatment for both male and female sexual problems. Tribulus
has been widely tested for its efficacy in enhancing sperm quality
and mobility, and for increasing libido and sexual performance in
experimental animals and men. It is also widely used as a body building
substance. Tribulus administration results in an increase of Luteinizing
hormone (LH) levels by 72%, and free testosterone levels by 41%.
Recently, tribulus has been clinically proven
to improve sexual desire and enhance erection. Researchers at the
Surabaya School of Medicine and Naval Hospital, Indonesia, studied
Protodioscin (PTN), a phytochemical agent isolated from Tribulus
terrestris. They found that tribulus works via the conversion of
protodioscine to DHEA.
Animal studies are beginning to shed light on
how tribulus extracts exert their proerectile effect. Researchers
working with New Zealand white rabbits measured the ability of oral
tribulus to relax corpus cavernosa tissues--necessary for achieving
erections. Their study found that the active ingredient in tribulus,
protodioscin, worked by increasing corpus tissue responses to acetylcholine,
nitroglycerin and electrical field stimulation. The researchers
concluded that the enhanced erections and aphrodisiac effects observed
with tribulus were due to increases in the release of nitric oxide
(NO) from the endothelium and nitrergic nerve endings.
Muira puama (Ptychopetalum olacoides) is a Brazilian shrub with
a long history in South American folk medicine as an aphrodisiac
and sexual tonic for promoting virility and treating impotence.6
Human studies have substantiated the use of muira puama for improving
libido and treating erectile dysfunction. In one study conducted
at the Institute of Sexology in Paris, France under the supervision
of Dr. Jacques Waynberg, 262 male patients experiencing lack of
sexual desire and the inability to attain or maintain an erection
were treated with 1 to 2.5 grams of muira puama extract a day. Following
two weeks of treatment, 51 percent of those suffering from erectile
dysfunction reported significant improvement. Additionally, 62%
of the patients suffering from loss of libido reported that the
muira puama extract had, in the words of the researchers, "a
dynamic effect."
A second study conducted by Dr. Waynberg included
100 men who complained of impotence, loss of libido and sexual difficulties
due to 'asthenia,' described as fatigue, loss of strength, or debility.
Following treatment with Muira puama, 66% of the men reported a
significant increase in frequency of intercourse. Of 46 men complaining
of loss of desire, 70% reported that treatment with muira puama
increased libido.
Another important measure of sexual function,
stability of erection during intercourse, was improved or restored
in 55% of the patients. Other benefits reported included a reduction
of fatigue, improved sleep, and increased morning erections. Treatment
with muira puama was much more effective in cases with the least
psychosomatic involvement. Of the 26 men diagnosed with common sexual
asthenia without noticeable sign of psychosomatic disorder, the
treatment was effective for asthenia in 100% of cases, lack of libido
in 85% of cases, and for inability of coital erection in 90% of
cases.
Sexual arousal occurs not just in the genitals but in the whole
body and, especially, in the brain. For men, it actually begins
when the brain sends impulses down the spinal cord and out to the
nerves that serve the penis. These impulses trigger the production
of nitric oxide (NO), which causes penile arteries to dilate and
the spongy core of the penis to relax and become engorged with blood.
The neurotransmitter that carries the sexual message is acetylcholine
(ACh). ACh also seems to control sexual behavior through its activity
in the brain. For women, ACh is also a very important part of sexual
function.
Numerous studies confirm a key role for cholinergic
nerve transmission in sexual responses. Simply speaking, with too
little ACh, sexual activity goes down. Increase ACh levels, and
sexual activity goes up. ACh is involved in the build-up toward
orgasm and the urethral and vaginal contractions that occur during
orgasm as well as the subjective perception of orgasm intensity
and duration.
In addition to its direct role in the sexual response,
ACh is also the primary chemical the body uses to transmit signals
from nerves to skeletal muscles, the muscles that move the body.
You need this chemical for muscular control and proper muscle tone.
There is reason to believe that enhancing cholinergic neuromuscular
transmission will enhance your energy and stamina by raising your
ACh levels and that this can provide indirect sexual benefits by
allowing you to perform longer and with more energy.
While drugs can enhance the body’s cholinergic
activity, these drugs not only have unpleasant or even dangerous
side effects, but are available only by prescription. One way to
safely and effectively enhance ACh levels is to take supplements
of choline, along with vitamin B5, so that the body will manufacture
more ACh.
Vitamin B5, also known as pantothenic acid or calcium pantothenate,
actually seems to enhance endurance by two routes. The first is
its already-mentioned role in creating ACh from choline. Second,
is its role in the energy-producing Krebs’ Cycle, which is
vital for all living cells. An early indication that vitamin B5
might increase physical endurance came from a study in which rats
were placed into a tank filled with cool (64°F) water and forced
to swim until they became exhausted. Prior to their swim, the rats’
diets had included either high, adequate, or deficient levels of
vitamin B5. The high-dose rats lasted more than four times as long
as those whose diet had been B5 deficient.
Ginkgo biloba is a highly regarded herb that has been proven to
improve blood flow, enhance oxygenation of tissues, protect blood
vessels from free radical damage, and restore elasticity and tone
to the entire circulatory system. These impressive properties make
ginkgo biloba especially effective for improving sexual functioning
and health in both men and women.
Because circulatory problems are a major factor
in impotence, researchers studied ginkgo to measure its effectiveness
for treating erectile dysfunction caused by impaired blood flow.
In one study, ginkgo was found effective in improving erectile dysfunction
in a group of impotent males taking 60 mg of ginkgo extract for
six months. Researchers suggested that ginkgo worked by stimulating
the release of nitric oxide (NO) which, as described earlier, signals
the blood vessels to dilate and sends blood to the corpus cavernosum
to achieve and maintain an erection.
Ginkgo’s positive effects on impotence were
further established by a second study, reported in the Journal of
Urology , in which researchers found that ginkgo was highly effective
in helping men achieve and maintain erections. According to the
study authors, the improvements were due to the direct effect of
ginkgo extract to enhance blood flow in arteries and veins.
Given ginkgo’s proven ability to dilate blood vessels and
improve blood flow to the penis, it is not surprising to note that
many aphrodisiac formulas contain ginkgo extract. According to Dr.
Stephen Karch, a specialist in cardiac pathology and author of The
Consumer’s Guide to Herbal Medicine, ancient Chinese herbalists
referred to ginkgo as an aphrodisiac. Karch reports that ginkgo
enhances nitric oxide (NO) production. Nitric oxide is the primary
messenger molecule that is affected by Viagra, and is the key factor
in helping achieve erections by informing certain blood vessels
to relax.
In Asia, ginseng has a long history of use in herbal formulas for
the treatment of sexual dysfunction. Recent studies in laboratory
animals have shown that ginseng enhances libido and sexual performance.
These effects of ginseng may not be due to changes in hormone secretion,
but to direct effects of ginseng, or its ginsenoside components,
on the central nervous system and gonadal tissues. Indeed, there
is good evidence that ginsenosides can facilitate penile erection
by directly inducing the vasodilatation and relaxation of penile
corpus cavernosum. Moreover, the effects of ginseng on the corpus
cavernosum appear to be mediated by the release and/or modification
of release of nitric oxide from endothelial cells and perivascular
nerves. Ginseng has also been found to affect the central nervous
system, significantly altering the activity of hypothalamic catecholamines
involved in sexual behavior and hormone secretion. Recent findings
that ginseng treatment decreased prolactin secretion also suggest
a direct nitric oxide-mediated effect of ginseng on the pituitary.
Additional studies lend growing support for the use of ginseng in
the treatment of sexual dysfunction and provide increasing evidence
for a role of nitric oxide in the mechanism of ginsenoside action.
A healthy sex life contributes to an improved quality of life and
can have profound ramifications on emotional and physical well being.
The compounds discussed here have been shown, singly and in combination,
to be effective in supporting recovery from sexual dysfunction.
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