sdyer@bbncc5.UUCP (Steve Dyer) (07/29/85)
I don't know why I didn't think of this before, but I have an interesting
personal anecdote which is possibly a demonstration of the competition
of amino acids for transport across the blood-brain barrier.
A few years ago, I was participating in a volunteer, double-blind study of
the effects of oral tryptophan, a common amino acid, on social behavior.
Tryptophan is a precursor of serotonin, a neurotransmitter, in much the
same way that phenylalanine is the precursor of dopamine and
norepinephrine. A dose of 2-4 GRAMS (i.e. a LOT) has been used as an
expensive sleeping pill, and subjectively, the effect is much like the
drowsiness after a meal: mild, not particularly enjoyable or reinforcing,
and not at all like being drunk.
A group of us were being observed sitting around playing board games and
chatting, and after an hour or two, it became pretty easy to guess who had
the tryptophan. We were served dinner, consisting of calzones, pizza and
fruit, and lo and behold, no sooner had any of us eaten (we had fasted for
a few hours before), that a few minutes later, any drowsiness we were
experiencing had disappeared. The effect was quite dramatic and
repeatable, for at the end of the double-blind study, each subject's
guess about tryptophan/placebo turned out to be correct. Whenever
anyone had received tryptophan, eating the meal abolished any subjective
drug effect (I don't know about the social interactions--I haven't seen
the published study.)
Although this is only an educated guess, the theory of competition
among amino acids across the blood-brain barrier makes a lot of sense
when trying to explain our subjective experiences.
--
/Steve Dyer
{decvax,linus,ima,ihnp4}!bbncca!sdyer
sdyer@bbnccv.ARPA