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Male Impotence Drugs May Deserve A Second Look In Women
New studies indicate the three drugs used to treat male
impotence also appear to work in
females, albeit a little differently, and should
give the scientific community pause to take a
second look at their potential in the 40
percent of women who report sexual dysfunction,
researchers say.
In one of the first studies of the effect of
phosphodiesterase Type 5 inhibitors
Viagra,Levitra and Cialis - on the pudendal arteries that
supply the penis, vagina and
clitoris the blood needed to produce a satisfying sexual
experience, Medical College of
Georgia researchers showed the drugs relax the artery in
male and female rats.
"It shows the drugs need to be investigated more for women
and small alterations could
make these compounds more effective for women living
with these disorders," says Dr.
Kyan J. Allahdadi, postdoctoral fellow in
physiology at MCG. He's presenting the findings
during the 122nd Annual Meeting of
the American Physiological Society held in New
Orleans April 18-22 as
part of the Experimental Biology 2009 scientific conference.
Although there was talk years ago of a pink pill for women
to parallel the blue Viagra for
men, early clinical trials found essentially no response
in women.
MCG researchers decided to look again, first giving a drug
to constrict the internal
pudendal arteries in male and female rats - as they would be
in a non-erect state - then
giving doses of each impotency drug to see the impact.
The arteries from male rats
displayed a relatively standard concentration-dependent
relaxation - the more drug they got,
the more they relaxed - while in females
arteries, there was an initial relaxation then an odd
oscillation between relaxation and
contraction with subsequent dosing.
While they don't fully understand the swing, the unique
female response likely provides
more evidence that sexual function is more complex
in females, says Dr. R. Clinton Webb,
chair of the MCG Department of Physiology and
a study author. Scientists define female
sexual dysfunction as a
multifaceted disorder that includes anatomical, psychological,
physiological and
social-interpersonal aspects.
MCG researchers have shown part of that complexity may be
the smooth muscle cells in
the internal pudendal arteries of females
communicate, agreeing to contract and relax, while
male smooth muscle cells make independent
decisions to just relax.
They found one other distinction: females were more
sensitive to Viagra®, or sildenafil,
while males were most sensitive to Levitra®, or
vardenafil.
Previous studies on the effectiveness of these drugs focused
on the cavernosal tissue, or
penis. The internal pudendal artery actually feeds the
penile artery which is buried deep in
the penis where numerous caverns enable it to be
flaccid when not engorged with blood.
Physical stimulation of the area causes the
tissue, endothelial cells and nerves to release
nitric oxide, a powerful dilator of blood
vessels. The system works pretty much the same
way in the vagina and clitoris.
"If you have too much constriction or not enough relaxation
to allow blood to go through
the internal pudendal artery, you are not going to
get the net effect of an erection," Dr.
Allahdadi says. "That is why we wanted to
begin to characterize what was going on in this
blood vessel."
Perhaps as importantly, the MCG scientists and others are
beginning to believe sexual
dysfunction provides an early, or at least visible, clue of
vascular disease. Vascular
problems, that can result from diabete, hypertension, high
cholesterol and the like, are a
major cause of sexual dysfunction in men and women. "You
don't feel atherosclerosis but
you know darn well if you are not
getting an erection," Dr. Webb says. In fact, the MCG
scientists are beginning to look at
animal models of disease states, such as diabetes, to see
what it does to these
internal pudendal arteries.
"What we have seen preliminarily is there is big difference
in responsiveness in these
arteries. The diabetic pudendal arteries are much more
sensitive to contraction," Dr.
Allahdadi says. They will look at how drugs like Viagra
impact that contraction in the days
ahead.
In fact MCG scientists suspect one reason that many of the
women participants in previous
studies of Viagra did not seem to respond is
because they did not have vascular problems
that could have been circumvented by a
drug that relaxes arteries so blood can enter. In
men with a healthy vasculature, the
drugs likely would still produce a longer erection.
Dr. Rita C. Tostes, associate professor in the MCG
Department of Physiology, is a co-
author who contributed to the design and analysis of the
study.
Courtesy of
http://www.medicalnewstoday.com
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