Feature Article
Viagra (Sildenafil citrate), which millions of men take for
erectile dysfunction (ED), reduces the effects of hormonal
stress on the heart by half, according to a study published
online in the journal Circulation.
Viagra causes genital blood vessels to expand, which helps
in maintaining an erection. Recent research also has
pointed to its potential usefulness in treating pulmonary
hypertension. Prior to the latest findings by a team of
Johns Hopkins researchers, it was thought to have little
effect on the heart.
Viagra, or sildenafil, blunts the strengthened heart beat
caused by chemically induced stress, according to study
senior author and cardiologist David Kass, MD, a professor
at the Johns Hopkins University School of Medicine and its
Heart Institute. It thereby lessens both the excess amount
of blood and the force used to pump it to the body.
"Sildenafil effectively puts a 'brake' on chemical
stimulation of the heart," says Kass.
Prevents and Reverses Effects of High BP
These findings are believed to be the first confirmation in
humans that Viagra has a direct effect on the heart. In
earlier research, Kass and his team observed a similar
effect in mice; Sildenafil blocked the short-term effects
of hormonal stress in the heart.
Related studies by the group show that sildenafil also
prevents and reverses the long-term effects of chronic high
blood pressure on the heart.
Sildenafil reversed the negative effects on heart muscle
weakened by heart failure and enlargement -- a condition
called hypertrophy -- in mouse experiments Kass and his
team carried out earlier this year. They reported their
results in the journal Nature Medicine.
"But we had no firm evidence as to whether or how this
therapy might work in the human heart," says Kass. "Our
latest research provides firm evidence this drug does
indeed have an important impact on the heart."
Increased Heartbeat Was Slowed
Thirty-five healthy men and women, with an average age of
30 and no previous signs of coronary artery disease,
participated in the six-month Johns Hopkins study. Within a
three-hour timeframe, each participant received two
separate injections of dobutamine (5 micrograms per
kilogram for five minutes), a synthetic, adrenaline-like
chemical that increases heart rate and pumping strength.
Between injections, study participants were assigned
randomly to a group that was treated with sildenafil (100
milligrams taken orally) or to a group given a sugar pill
placebo. All participants then were given the second
dobutamine injection to see what effects sildenafil or
placebo had on the heart.
Measurements of heart function were made before and after
each injection. These included blood pressure readings,
electrocardiograms and echocardiograms. Blood samples
confirmed relatively equal levels of sildenafil and other
enzymes.
Each dobutamine injection stimulated heart function,
increasing heart rate and the force of each heartbeat used
to pump blood throughout the body, results showed.
"This stimulation is similar to the way the nervous system
normally increases heart function when triggered by
emotional or exercise stress, or in diseases such as heart
failure," notes Kass.
After the first injection of dobutamine, the force of heart
contraction increased by 150 percent in both groups. In the
placebo group, this increase repeated itself after the
second injection. However, in the group treated with
sildenafil, the increased heartbeat was slowed by 50
percent, resulting in a smaller increase in blood flow and
blood pressure generated by the heart in response to
chemical stimulation.
Between injections, heart function was not altered in the
sildenafil group, demonstrating the absence of adverse side
effects on the resting human heart.
Stops PDE5A Action
"Knowing more about the effects of sildenafil on heart
function will allow for safer evaluation of its use as a
treatment for heart problems," says Kass.
"Our results set the stage for further studies of
sildenafil's immediate and long-term effects on the heart
and its ability to modify other neurohormonal and stress
stimuli, including adrenaline and hypertension," he adds.
While the precise biological actions of sildenafil in the
heart are not fully understood, the drug is known to work
by stopping the action of an enzyme, called
phosphodiesterase 5 (PDE5A), Kass explains. This enzyme is
involved in the breakdown of a key molecule, cyclic GMP,
which helps control stresses and limit overgrowth in the
heart.
PDE5A is also the biological pathway that sildenafil blocks
in the penis to prevent the relaxation of blood vessels and
thus maintain erections.
About this: - Rita Jenkins is a health journalist for Daily News Central,
an online publication that delivers breaking news and
reliable health information to consumers, healthcare
providers and industry professionals: