Wednesday, November 28, 2012

How Does Nitroglycerin Stop Heart Attacks?

Dear Cecil:

Recently a friend of the family had a heart attack. While he was in the hospital, they gave him nitroglycerin pills to stop the attack and ease his chest pains! I consider myself as having a rational mind, but the ingestion of explosives (no matter how small the amount) does not on the surface seem to be a great way to promote cardiovascular health! In fact, it would seem that nitro might have caused a few heart attacks (especially around the Fourth of July). How does nitroglycerin stop heart attacks?

— Steve S., Salt Lake City


People nowadays are such wimps. If you're looking for strong medicine, how can you do better than a high explosive? The nitroglycerin in the pills, patches, and sprays that heart patients use for angina (chest pain) is in fact the same stuff you find in dynamite--the residue the drug leaves on patients' skin and clothing is often enough to set off airport bomb-sniffing machines. The medicinal dose is tiny and diluted with inert material, so it's completely nonexplosive; even so, nitroglycerin is one medicine I'd hesitate to shake before use.

I'm kidding, of course. Still, straight nitroglycerin (an oily yellow liquid) isn't something you'd want to take a swig of--even if we ignore the fact that it's poisonous, the merest jolt will detonate it. The man who discovered it in 1846, Italian chemist Ascanio Sobrero, had his face scarred by a laboratory explosion. The Swedish inventor of dynamite, Alfred Nobel, made his pile after figuring out in the 1860s that mixing nitro with diatomaceous earth would produce a relatively stable explosive paste that was much safer to use.

Laborers in Nobel's factories were the first to feel nitroglycerin's therapeutic effects. When they arrived at work each morning, those with heart problems found that their chest pains subsided (though almost everybody on the job noticed that sometimes their heads hurt like hell). Turned out the nitroglycerin vapor in the factory air was acting as a vasodilator, increasing blood flow both to the heart (which needed it, at least in the case of the angina sufferers) and to the head (which didn't).

Nitroglycerin pills have been a standard treatment for angina and heart attack symptoms since 1879--doctors prescribed them for Nobel himself not long before his death in 1896 (he refused to take them--couldn't brook the headaches). But more than a century passed before scientists understood how they worked. In the 1970s, researchers established that the body converts nitroglycerin into nitric oxide, and in the '80s they demonstrated that nitric oxide is a messenger molecule that tells the smooth muscles surrounding blood vessels to relax. (A heart attack basically means that not enough blood is reaching your cardiac muscles.) In 1998 three scientists who'd been instrumental in unlocking the mystery of nitroglycerin were collectively awarded--I'm telling you, this story has irony out the wazoo--the Nobel Prize in medicine.

by Cecil Adams, The Straight Dope |  Read more:
Photo: Everyday Health