Effect Measure

There is a lot of science stuff in newspapers that is just (barely) warmed over press releases from companies or universities. They get pushed out into the world via aggregating services like Eurekalert. Lots of science bloggers and journalists use this stuff for ideas and sources, but even when the origin is a university you have to be circumspect. Some of it is gross over reaching, probably by scientists being pushed by university media relations types trying to get some ink for their institution and not caring how much sense it makes. At least that’s how I read this piece on Eurekalert pawned off on an unsuspecting but prurient public by Texas A&M University:

Watermelon may have Viagra-effect

A cold slice of watermelon has long been a Fourth of July holiday staple. But according to recent studies, the juicy fruit may be better suited for Valentine’s Day.

That’s because scientists say watermelon has ingredients that deliver Viagra-like effects to the body’s blood vessels and may even increase libido.

“The more we study watermelons, the more we realize just how amazing a fruit it is in providing natural enhancers to the human body,” said Dr. Bhimu Patil, director of Texas A&M’s Fruit and Vegetable Improvement Center in College Station.

[snip]

In watermelons, [beneficial ingredients] include lycopene, beta carotene and the rising star among its phyto-nutrients – citrulline – whose beneficial functions are now being unraveled. Among them is the ability to relax blood vessels, much like Viagra does.

Scientists know that when watermelon is consumed, citrulline is converted to arginine through certain enzymes. Arginine is an amino acid that works wonders on the heart and circulation system and maintains a good immune system, Patil said.

“The citrulline-arginine relationship helps heart health, the immune system and may prove to be very helpful for those who suffer from obesity and type 2 diabetes,” said Patil. “Arginine boosts nitric oxide, which relaxes blood vessels, the same basic effect that Viagra has, to treat erectile dysfunction and maybe even prevent it.”

While there are many psychological and physiological problems that can cause impotence, extra nitric oxide could help those who need increased blood flow, which would also help treat angina, high blood pressure and other cardiovascular problems.

“Watermelon may not be as organ specific as Viagra,” Patil said, “but it’s a great way to relax blood vessels without any drug side-effects.” (Eurekalert)

What a load of crap. Let’s just stick with the Viagra connection. Yes, it’s true that Viagra works through a mechanism that involves nitric oxide (let’s just say NO). Since the most important sex organ in the human body is the one between your ears, erections begin with signals from the nervous system, specifically the subsystem called the parasympathetic nervous system. Nerve firing in the parasympathetic system produces release of the neurotransmitter, nitric oxide, causing smooth muscle relaxation around arterial walls in the penis with increased blood flow into the spongy tissue of the corpus cavernosum. Engorgement of the corpus cavernosum produces the erection. Nitric oxide accomplishes this by activating the enzyme guanylate cyclase which in turn increases levels of cyclic guanosine monophosphate (cGMMP). It is cGMP that leads to the relaxation of smooth muscles in the helicine arteries. If the arteries constrict then the erection deflates (or, as we docs say, detumesces). This happens when the NO-induced cGMP is degraded by another enzyme phosphodiesterase type 5 (PDE5). Viagra is an inhibitor of PDE5. Thus the erection lasts longer (and it may even be longer). But the erection doesn’t happen without the original sexual stimulation that produces the NO in the first place (which is why the TV ads can say a male on Cialis, a similar drug to Viagra, has up to 36 hours without spending it doubled over or wearing a raincoat).

So when the watermelon promoting scientists say that the fruit “watermelon may not be as organ specific as Viagra” they aren’t kidding. Watermelon isn’t a PDE5 ihibitor. It has a an ingredient that participates in the formation of NO (nitric oxide). So does pornography. It would have been more accurate to say that watermelon may have a pornography-like effect than that it has a Viagra-like effect. And it still would have gotten everyone to read the presser.

One thing that’s certainly accurate about the press release:

“Watermelon may not be as organ specific as Viagra,” Patil said, “but it’s a great way to relax blood vessels without any drug side-effects.”

We can safely say no matter how much watermelon you eat it won’t cause you to have an erection lasting more than four hours. You might have a pretty good bowel movement, though.

Comments

  1. #1 Greg Laden
    July 2, 2008

    You can die from eating too much watermelon, of course.

  2. #2 Greg Laden
    July 2, 2008

    No, no, wait wait, how’s this:

    If this watermelon give you an erection lasting more than four hours, see your grocer….

  3. #3 Richard Eis
    July 2, 2008

    If this watermelon give you an erection lasting more than four hours, see your grocer…

    because he is clearly selling some good stuff there.

  4. #4 Tye
    July 2, 2008

    quick note here. I worked at A&M (and did my undergrad work there) and helped to develop the seedless black diamond watermelon. The one thing I learned from this process is that there is a huge amount of money and pressure coming from co-op growers, multi-national farms, and the state agriculture extension to promote the values of specifically bred crops.

    Also in the paper is a short summation of how the deep red melons now contain more lycopene than tomatoes. Of course the probable health benefits of lycopene are espoused afterwards.

    I guess my point is, although there were some good points in the paper and something definitely worth mention, I agree with revere on this one that somewhere along the line from data to publish an agenda was pushed through by someone. Even seemingly innocuous research can be branded to grab public attention.

  5. #5 Ana
    July 2, 2008

    Aphrodisiacs: some, potent thru visual metaphors, or if one likes, iconic slippage: oysters (worked on me once, the first time I ate them!), horn of rhinoceros, penis of the tiger, ginseng, etc.

    Or just plain old Love Potion number 9, whoo aaa…

    Watermelons? Yikes. According to the article, it is men who are supposed to partake and get the benefits, or have I got that wrong? Odd as the watermelon is not a symbol of male potency – but of exaggerated feminine attributes. This is definetly a very NOVEL symbolic shift ;)

  6. #6 Julian
    July 2, 2008

    Oysters.. Geh *shudder* I can’t think of a more disgusted food to eat. Unless they’re fried past all recognition those shell-dwelling ocean slugs can stay at the bottom of the ocean thankyouverymuch.

  7. #7 Mario
    July 2, 2008

    Of course, what does Dr. Patil know about human
    physiology and sexual response, being as his specialty
    is vegetables? I would suspect he knows about as
    much as the average person. The minute he starts talking
    about behavioral or biological mechanisms in the human body, he crosses over from science to charlatanism.

  8. #8 newore
    July 2, 2008

    … or maybe it’s the water giving the well known ‘piss hardon’.

    I couldn’t resist.

  9. #9 katherine sharpe
    July 3, 2008

    well, I clicked on ‘the viagra-watermelon connection,’ so A&M’s ruse worked on me, too.

    i would have guessed that watermelon had pretty much no nutritional content at all, though. so i guess i learned something, as a side effect.

  10. #10 Neil B
    July 3, 2008

    I like watermelon, and this is nice to know despite the OPs caveats and disenthusiasm. I wonder, wouldn’t it be easier to buy arginine tablets, and has anyone tried that?

  11. #11 daedalus2u
    July 3, 2008

    There are problems with trying to modify one’s NO status via diet, in general it doesn’t work long term, at least not by any methods that have been tried. There is a non-dietary method I am working on, but it isn’t generally accepted yet.

    Methods that don’t work include so-called NO donors (such as nitroglycerine which isn’t really an NO donor but it has some NO-donor-like properties and other organic nitrates) they cause what is called “nitrate resistance”. Amyl nitrite does cause acute NO effects and is sometimes used as a sexual stimulant (don’t confuse with amyl nitrate). Long term or chronic use would cause nitrate resistance. L-arginine causes “arginine resistance”. This is thought to be due to generation of potent inhibitors of nitric oxide synthase by physiology, the various methyl arginines. The presence of these inhibitors is thought to explain why acute arginine does stimulate nitric oxide synthase but chronic arginine doesn’t. NO physiology is extremely important and is extremely well regulated. It is very hard to perturb without causing adverse side effects. Viagra does cause adverse side effects in things such as sleep apnea. I suspect that is because inhibition of the PDE5 increases cGMP levels and causes feedback inhibition of NOS via cGMP mechanisms. Then NO effects not mediated through cGMP are reduced (for example triggering breathing).

    Inorganic nitrates do have acute effects. That is thought (by some) to be a major factor in the health effects of eating green leafy vegetables, they contain a few tenths of a percent nitrate. That nitrate is well absorbed, is concentrated ~10x into saliva and commensal bacteria on the tongue reduce it to nitrite. After ~100 grams of lettuce salivary nitrite can reach 2 mM/L. There is some thought that the nitrite in saliva is the reason for the common folk remedy for impotence, applying saliva to certain regions of skin. Skin has a lot of xanthine oxidoreductase which reduces nitrite to NO which can then activate the pathways Revere talks about locally. When saliva is swallowed, the nitrite is reduced to NO by the low pH in the stomach and NO levels of ~100 ppm have been measured (that is ppm, not ppb which the nasal passages generate). 100 ppm NO is nontoxic, but in contact with air it forms NO2 which is toxic at a few ppm level. It is the NO2 in silo gases that kills people. That NO2 is from nitrate in silage being reduced to nitrite and to NO and then being oxidized to NO2 in air.

    Watermelon may have a lot of nitrate. I looked to see if I could find a reference for the nitrate content of watermelon juice but I couldn’t. The sap of most plants has ~0.1% or so nitrate, but juices of fruits often don’t have that much. Lettuce and spinach do have a few tenths of a percent nitrate perhaps that is the mechanism behind Popeye’s prodigious strength. Acute NO from nitrate likely wouldn’t cause acute strength increase, but canned spinach sometimes contains nitrite from the reduction of nitrate. That would have more prompt effects than nitrate. Mitochondria biogenesis is triggered by NO, so consumption of spinach and lettuce might be therapeutic for disorders associated with insufficient mitochondria, such as chronic fatigue and conditions characterized by hyperlactatemia.

  12. #12 R
    July 3, 2008

    Love the title, was the pun “it’s not hard” intended? My old professors in journalism would get a kick… Couldn’t resist commenting on that.

  13. #13 revere
    July 3, 2008

    R: Moi? Make a pun like that? How could you even suggest such a thing!

  14. #14 Polyester Mather D.D.
    July 3, 2008

    Of course, the watermelon may also be spiked with gin , by injection, in which case the wonder fruit may be used as a miracle truth serum . Imagine what Christophe Hitchens might reveal about the Editors of Vanity Fair if subjected to watermelon boarding using a quality product like Beefeater or Bombay sapphire as an adjuvent?

  15. #15 1Watt, Hermit
    July 3, 2008

    or you could just drill an appropriately sized hole….

  16. #16 MarkH
    July 6, 2008

    Ah Daedalus, how did I know I’d find you on this thread?

    This is, of course, total claptrap. There is no evidence providing large amounts of constituents of the process of SMC regulation will cause you to get erections. Otherwise nitro would give every angina sufferer priapism. You either need local delivery (amyl nitrate as daedalus describes) or a specific drug, like sildenafil.

    Now, everyone contemplate the American Pie type implications of these facts, and let’s see how appealing watermelon is now…

  17. #17 AnnieRN
    July 9, 2008

    Shucks–I guess I won’t wait for “Smiling Bob” to show up here, then….

  18. #18 Thane of Towson
    February 7, 2009

    I am over 65. My penis used to say, “Just get me to the opening, and I will take it from there.” Now my penis needs a hand—anybody’s hand. Viagra just gives you a piss hard-on. Remember those? The girls used to climb on in the morning thinking the hard-on was for them. If you can’t get it hard on its own, there is not better living through chemistry. Not for the male members anyway. And let’s take a good look at the female that penis is attempting to have sex with. Most do not look like the chicks in the commercials.

  19. #19 sonatherun
    USA
    April 12, 2013

    I’d much rather eat a lot of watermelon for all it’s benefits, even if it’s shilled by someone from Texas A&M, than listen to a shill for Pfizer.

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