My cross country and track coach is vehemently opposed to people on
the team drinking.  He claims that after a week of aerobic training to
build capillaries, drinking 6 beers on a Saturday night will collapse
the capillaries and negate the training that was done.  I want to know
if you can find any scientific study that either supports or
discredits this assertion.  I know alcohol has other negative effects
on the body, but I'm only interested in those short term effects that
would directly affect in season athlete, specifically the collapsing
of capillaries.  (I also know that dehydration is caused by alcohol
and could affect training, but that can easily be adjusted for.)

This site says the following: (http://www.ucheepines.org/alcohol.htm)

"One of the little-known injuries of alcohol is that it causes
clustering of red blood cells which block tiny blood capillaries,
resulting in a reduction of blood to the brain and muscles, and
reduced muscular coordination, mental activity, and an impairment of
judgment."

However, the credentials of the writer aren't given.  Only that the
website is the home a "lifestyle illness institute" founded by Calvin
Thrash, M.D., specialist in Internal Medicine, and his wife, Agatha
Thrash, M.D., board specialist in pathology, is known.

This one looks more promising:
(http://www.niaaa.nih.gov/publications/arh21-1/76.pdf)

"First, alcohol can directly disturb the integrity of the mucosal
epithelium. Second, alcohol induces the release of noxious signaling
molecules, such as cytokines, histamine, and leukotrienes. These
substances can damage the small blood vessels, or capillaries, in the
intestinal mucosa and induce blood clotting. Such clotting may lead to
an impaired transport of fluids across the capillaries; fluid
accumulation under the tips of the villi; and, eventually, destruction
of the tips of the villi. The resulting lesions allow large molecules,
such as endotoxins and other bacterial toxins, to enter the
bloodstream and the lymph.  Third, as in the stomach, decreased
prostaglandin synthesis may contribute to changes in the capillaries
and to the development of mucosal injury."

Warning: I'm not a doctor, or anything like one.  ...but it sounds to
me like it's more complex than big capillaries / little capillaries;
more specifically, alcohol causes capillaries to function improperly
because they become clogged (or clotted), not because they're
constricted.

These seem to be more related to longer term effects and diseases. 
I'm more interested in short term effects related to athletics.  Since
I question whether there's any truth behind my coach's assertion,
there could very well be no information on it to be found.

Thanks Anyways

I have a background in biology, as well as plenty of experience
running and drinking as at a collegiate level.  Before anything, you
did not say if you were in high school or college, but keep this in
mind (though it mostly pertains if you are in high school, and more
"impressionable"): your coach may just want to steer you away from
alcohol, because in the long term in large amounts, yes alcohol can
lead to quite nasty problems, and he may be trying to use athletics as
a means to do so.

We have reached a general consensus among us runners, as well as with
my coach who is an honest guy about this stuff.  First, there is no
way to quantify these changes, and I highly doubt any particular and
reliable study has been conducted in an attempt to do so, so saying
"the effects from the last 6 days have been negated" is pretty
ridiculous (you can't even quantify the benefits of workouts over 6
days, running just doesn't work like that, short term and long term
cardiovascular stresses and recovery cumulate in strange and
unpredictable ways).  Second, our combined experience has led to the
conclusion that drinking will not negatively affect your running,
given the following conditions: a) you don't get too dehydrated during
the night (drink some water before you go out) nor throuh the night
(drink a LOT of water when you get home)  b) you don't pass out and
sleep through your sunday long run c) you arn't hung over and
therefore can't run on sunday.  Dehydration is a realistic fear, and
dehydrated muscles will be weak, sore, and unresponsive for a day or
two following a night out drinking.

Second, the effects of alcohol described in the other comments are
most definitely long term effects, and most likely for someone who has
been drinking moderately to heavily for many years.  You don't get
cirrhosis of the liver overnight, nor will just a few drinks alter the
mucosal epithelium.  When looking for information on this, make sure
you separate out long term and short term effects.

Third, it is almost universally accepted that alcohol has both
negative and positive effects on the cardiovascular system, although
generally the positive are only seen when only a drink or two is had
per day, while the negative effects are associated with binge or
high-volume drinking.  A very good summary is at: [
http://chemcases.com/alcohol/alc-10.htm ] The mechanism behind the
positive effects is not very well known at all.  Physiologically, my
theory is that the forces at work creating the positive effects are
for most people outweighed by the negative effects of drinking say, 6
beers in an evening.  But look at us runners: generally strong, young,
healthy people.  I believe that the negative effects of alcohol are
vastly more well-tolerated by a strong healthy person, so much so that
the known benefits are free to take place.  I won't go so far as to
say drinking  lot is good for you, but I do believe the posible
negative effects just are not very considerable to runners.  Many
famous collegiate and even olympic runners have had no problem with
drinking on various levels (think of Steve Prefontaine, he did his
fair share of partying, and oh, set how many national records?) but it
did not seem to be a problem.

In the end what I think it comes down to is: the naysayers have never
gone out on a saturday night, gotten massively drunk, then woken up
hungover the next day yet still gone out for a (quite possibly fuzzy)
15-mile sunday long run, and they simply do not understand the
relativeness of it all.  The effects of alcohol may be negative in
nature to most people, but they are nothing compared to the stresses
of a hard anarobic interval workout.  99 percent of the population
will never get ther heart rate above 200 bbm, nor have blurred visio
from voluntary physical exertion, and so on.  The alterations alcohol
does to your body are really minimal in comparison.  So, my argument
is basically that alcohol's effects are possibly negative in nature,
but are simply negligable to a runner.  Be glad that you are a fit
young person who can enjoy himself both socially and physically, cause
you only have one life in which to do it all.

Great comment andrewxmp, especially the last paragraph!  I am in
college, and my roommate (who didn't run) could never understand how I
could get up at 10:00 for my Sunday long run after partying all night
the night before.  I've actually found running to be the best cure for
a hangover.  Few (if any) people on the team believe my coach's
assertions, but I was just looking for something concrete to
support/refute them.  However, your comment was good enough that you
can feel to post it as an answer.

Two other short-term effects of alcohol that could affect your
training are a disruption of testosterone production and, of course,
secondhand smoke from most alcohol-serving venues.