The curse of jet lag has struck most international travelers
at one time or another -- and anyone lucky enough to have avoided it will surely
have suffered the equally unpleasant sleep-deprivation involved in an
early-morning start. Nor, as shift workers know too, is it possible to escape by
going to bed earlier the previous evening, and thus putting sleep in the bank.
Sleepiness is controlled by the body’s internal biological clock, so an earlier
bedtime just means several wakeful hours staring in frustration at a darkened
ceiling. For years, some travelers and shift workers have sworn
by melatonin (褪黑素). This is a hormone that regulates the biological clock. It is
made in the brain by a structure called the pineal gland (松果体), as darkness sets
in after sunset. Light is the one that keeps the biological clock in same pace
with solar time. The clock then tells the brain when to go to sleep. The theory
of those who use melatonin is that an external dose of it can reset the clock,
and thus cause the "go to sleep" signal to be sent at a more convenient moment.
Melatonin can also increase sleepiness during the day, when the pineal gland is
not producing it. This has resulted in a growing, and often
unregulated, market in melatonin-supplement tablets. The pharmaceutical
industry’s response to this seems to be: "If you can’t beat them, join them." A
paper in this week’s Lancet, by Shantha Rajaratnam of the Harvard Medical School
and his colleagues, reports two trials, funded by drug companies, of
tasimelteon, a substance that binds to the same receptors in the brain as
melatonin does, and which it is expected will have a similar effect.
In the course of these trials, more than 400 people had their bedtimes
brought forward by five hours in controlled conditions. Half an hour before
lights out, a quarter of them were given common drug, while the remaining
three-quarters were given varying doses of tasimelteon. Dr. Rajaratnam and his
colleagues report that the new drug let people fall asleep faster at the
unnaturally early time, and also allowed them to sleep longer than those given
the common one. When will melatonin be made in the brain according to the passage