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Circadian fix: Viagra may lessen effects of jet lag.



The leading drug prescribed for male impotence can counteract the lethargy caused by a disruption in the sleep cycle, a study in rodents suggests. Sildenafil sildenafil /sil·den·a·fil/ (sil-den´ah-fil?) a phosphodiesterase inhibitor that relaxes the smooth muscle of the penis, facilitating blood flow to the corpus cavernosum; used as the citrate salt to treat erectile dysfunction. , commonly known as Viagra, helps hamsters rebound from a 6-hour clock change such as a long eastbound plane flight produces.

To mimic conditions that can lead to jet lag jet lag

Period of adjustment of biological rhythm after moving from one time zone to another, experienced as fatigue and lowered efficiency. It reflects a delay in the synchronization of changes in the level of blood cortisol, the major steroid produced by the adrenal cortex
, scientists habituated hamsters to a daily routine of 14 hours of light and 10 hours of darkness. The researchers then abruptly switched on the lights 6 hours early and continued the same light-to-dark routine from that point onward, simulating the effects of a flight from Chicago to London.

Just before changing the hamsters' routine, the researchers injected each animal with either sildenafil or saline solution saline solution
n.
A solution of any salt, usually an isotonic sodium chloride solution. Also called salt solution.


Saline solution
A solution of sterile water and salt used in a variety of medical procedures.
. Then, they observed how long it took the hamsters to restart their daily habit of running on a wheel.

Hamsters receiving a large single dose of sildenafil resynchronized their body clocks and resumed their usual wheel routines within 6 days. Hamsters getting a lower dose took 8 days, whereas those receiving the inert injection took 12 days, the scientists report in an upcoming issue of the Proceedings of the National Academy of Sciences The Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United States National Academy of Sciences. .

Circadian rhythm in mammals is controlled mainly by neurons in the hypothalamus hypothalamus (hī'pəthăl`əməs), an important supervisory center in the brain, rich in ganglia, nerve fibers, and synaptic connections. It is composed of several sections called nuclei, each of which controls a specific function. , says study coauthor Patricia V. Agostino, a neuroscientist at the National University of Quilmes in Bernal, Argentina. When the vision system detects light, it sends stimuli to the hypothalamus and sets off a series of events that generate wakefulness wakefulness

believed to occur when the tonic flow of impulses from the reticular activating system exceeds the critical level for sustaining consciousness; reduction of reticular activating system activity is the basis of the pharmacological induction of sedation.
. "Light is the main synchronizer of the circadian circadian /cir·ca·di·an/ (ser-ka´de-an) denoting a 24-hour period; see under rhythm.

cir·ca·di·an
adj.
Relating to biological variations or rhythms with a cycle of about 24 hours.
 clock," Agostino says.

A compound called cyclic guanine guanine (gwä`nēn), organic base of the purine family. It was reported (1846) to be in the guano of birds; later (1879–84) it was established as one of the major constituents of nucleic acids.  monophosphate (cyclic GMP) plays a role in regulating circadian rhythm. In the hamster study, scientists measured the animals' blood concentrations of cyclic GMP 45 minutes before changing the light-dark schedule. Compared with hamsters receiving saline shots, the animals injected with sildenafil had double the amount of cyclic GMP. Sildenafil shuts down enzymes that would limit cyclic GMP production, but Agostino's team isn't certain that this is how the drug restores circadian rhythm.

"This resetting of the clock seems to be novel," says pharmacologist Joseph A. Beavo of the University of Washington School of Medicine The University of Washington School of Medicine (UWSOM) is a public medical school located in Seattle, Washington. It is a graduate school affiliated with the University of Washington, and is the only medical school in the states of Washington, Wyoming, Alaska, and Idaho.  in Seattle. He cautions that the new research is only on rodents, but since sildenafil is a widely used drug, a sampling of men who travel frequently and take it might turn up any stabilizing effect on circadian rhythm, he says.

Most travelers who experience jet lag find that the effects are strongest after an eastbound flight, which shortens the day and pushes the circadian clock forward. Interestingly, sildenafil's circadian re-adjustment worked only in animals whose circadian rhythms had been advanced, Agostino says. That suggests that the drug would work for eastbound travelers and airline personnel, as well as some shift workers, she says.
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Title Annotation:This Week
Author:Seppa, N.
Publication:Science News
Date:May 26, 2007
Words:457
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