Viagra, Hamsters, and Jet-Lag

Robert W. Griffith, MD

Hamsters are commonly used to study circadian rhythm - the changes in the body that occur at different times of the day - as they have quite exact daily rhythms; for instance, they run on their exercise wheels at the same time every night. This makes them ideal for modeling jet-lag, the phenomenon that is well-know to international travelers. A person traveling east has difficulty falling asleep and wakening for a few days, while someone traveling west falls asleep and wakes earlier.

Melatonin is an effective medication for many people to help overcome (or prevent) jet-lag. But now there's news of another candidate - Viagra® (sildenafil). Dr Diego Golombek of Buenos Aires has reported the effects of the drug in hamsters synchronized to a 24-hour day by simulating light-dark cycles. Shifting the light-dark phases forward 6 hours simulated west-to-east jet-lag. Hamsters given sildenafil achieved a return to their normal schedule of exercise 4 days faster, on average, than control hamsters given saline. Sildenafil had no effect if the light-dark cycle was switched to mimic westward travel.

Dr Golombek has a sound theoretical explanation for his findings. Sildenafil stops a brain chemical, cyclic GMP, from degrading. As cyclic GMP is involved in adapting to light, increasing its levels accelerates the hamsters' adaptation to the new time-schedule.

Human studies are the next step. I imagine there will be no great difficulty in getting volunteers for a clinical trial . . . But people shouldn't try Viagra for themselves in this indication until more is known about its effectiveness, safety, and the best dose.

By the way, did you know that Viagra can be used to delay plants from wilting? The mechanism of action is similar to that in erectile dysfunction in men: nitric oxide leads to the production of cyclic GMP whose degradation by phosphodiesterase-5 is inhibited by sildenafil.

Source
HealthandAge Blog

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