Should you take aspirin after you exercise?

I just got back from a beautiful four and a half mile walk around a reservoir behind my house.  I always take 2 adult aspirin after such things like this.  A recent paper implies that perhaps I should not [ Proc. Natl. Acad. Sci. vol. 114 pp. 6675 – 6684 ’17 ].  Here’s why.

Muscle has a set of stem cells all its own.  They are called satellite cells.  After injury they proliferate and make new muscle. One of the triggers for this is a prostaglandin known as PGE2 — https://en.wikipedia.org/wiki/Prostaglandin_E2 — clearly a delightful structure for the organic chemist to make.  It binds to a receptor on the satellite cell (called EP4R) following which all sorts of things happen, which will make sense to you if you know some cellular biochemistry.  Activation of EP4R triggers activation of the cyclic AMP (CAMP) phosphoCREB pathway.  This activates Nurr1, a transcription factor which causes cellular proliferation.

Why no aspirin? Because it inhibits cyclo-oxygenase which forms the 5 membered ring of PGE2.

I think you should still aspirin afterwards, as the injury produced in the paper was pretty severe — muscle toxins, cold injury etc. etc. Probably the weekend warriors among you don’t damage your muscles that much.

A few further points about aspirin and the NSAIDs

Now aspirin is an NSAID (NonSteroid AntiInflammatory Drug) — along with a zillion others (advil, anaprox, ansaid, clinoril, daypro, dolobid, feldene, indocin — etc. etc. a whole alphabet’s worth). It is rather different in that it has an acetyl group on the benzene ring.  Could it be an acetylating agent for things like histones and transcription factors, producing far more widespread effects than those attributable to cyclo-oxygenase inhibition.   I’ve looked at the structures of a few of them — some have CH2-COOH moieties in them, which might be metabolized to an acetyl group –doubt.  Naproxen (Anaprox, Naprosyn) does have an acetyl group — but the other 13 structures I looked at do not.

Another possible negative of aspirin after exercise, is the fact that inhibition of platelet cyclo-oxygenase makes it harder for them to stick together and form clots (this is why it is used to prevent heart attack and stroke). So aspirin might result in more extensive micro-hemorrhages in muscle after exercise (if such things exist).