Scientists in Argentina have shown that low doses of sildenafil (more commonly known as the brand Viagra) helped hamsters’ circadian rhythms to adapt more quickly to a new day-night pattern similar to eastbound jetlag.
Their findings are published in the early online edition of the US journal Proceedings of the National Academy of Sciences.
The research was conducted by Patricia Agostino and colleagues from the Laboratorio de Cronobiología (Chronobiology Laboratory), Departamento de Ciencia y Tecnología (Department of Science and Technology), Universidad Nacional de Quilmes, Buenos Aires, Argentina. Chronobiologists study the biological rhythms of organisms.
Mammals have a biological master clock that controls their circadian rhythm (sleep-wake cycle). The master clock is located in the brain, inside the hypothalamus in a region called the suprachiasmatic nucleus (SCN). The SCN controls the release of hormones and neurotransmitters that regulate a multitude of body and brain functions over a 24 hour period.
Light-activated brain signals play an important role in “training” the master clock to keep time.
Agostino and colleagues already knew that the master clock could be trained to a different 24 hour cycle, for instance as when people gradually adapt to being in London as opposed to New York, but they did not know exactly how the mechanism worked. They had a hunch that it depended on triggering an enzyme to make cGMP (cyclic guanosine monophosphate) and its related protein kinase PKG.
And they also knew that sildenafil (Viagra) enhanced the effect of cGMP by stopping it from being broken down by the enzyme phosphodiesterase 5 (PDE5).
So they injected low doses of sildenafil (Viagra) in hamsters and trained them to get used to an earlier daytime by switching lights on 6 hours earlier (like someone in London waking up before someone in New York).
The found that the hamsters who had the sildenafil (Viagra) adapted more quickly to the earlier daylight, for instance they were more active, as they would have been in real day time. It did not work for the reverse, in other words the equivalent of having jet lag from flying west, from London to New York for example.
They also showed that the SCN of the hamsters contained PDE5, leading them to surmise that the effect of sildenafil (Viagra) was to inhibit PDE5 which in turn increased cGMP and its related protein kinase PKG, thereby suggesting that they play a role in the speed with which the master clock adapts to environmental change.
Agostino and colleagues concluded that:
“These results suggest that sildenafil may be useful for treatment of circadian adaptation to environmental changes, including transmeridian eastbound flight schedules.”
There is a suggestion that these findings could point research in the direction of other drugs that affect cGMP levels, and one day they could be used to help shift workers, airline crew, and long-haul travellers or anyone who needs to adapt quickly to new time-shifts.
There is no suggestion that people start taking the currently available sildenafil (Viagra) for any other use except that for which it has been approved.
“Sildenafil accelerates reentrainment of circadian rhythms after advancing light schedules.”
Patricia V. Agostino, Santiago A. Plano, and Diego A. Golombek.
Published online before print May 22, 2007
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0703388104
Written by: Catharine Paddock
Writer: Medical News Today