July 3, 2008

Passion Fruit

By Ashley Meeks, Las Cruces Sun-News, N.M.

Jul. 3--LAS CRUCES -- "And you've been throwing them away all this time," said Darrell Durr.

The 31-year-old safety specialist at White Sands Missile Range was reacting Wednesday to the latest pop science tidbit on the airwaves, an alleged "Viagra effect" from watermelon, according to the research of Bhimu Patil, director of the Vegetable and Fruit Improvement Center at Texas A&M University in College Station.

In the spotlight is an amino acid concentrated in watermelon rind, citrulline, that has "an ability to relax blood vessels, much like Viagra does," according to a Monday news release about the research. "(W)hen watermelon is consumed, citrulline is converted to arginine ... (which) boosts nitric oxide, which relaxes blood vessels, the same basic effect that Viagra has, to treat erectile dysfunction and maybe even prevent it."

Patil did not return a call for comment Wednesday.

But Michael Rae, a Philadelphia researcher with the Methuselah Foundation and co-author of "Ending Aging," said the Viagra connection is as-yet unproved and unlikely to be caused by the microscopic amounts of the amino acid likely present in watermelon rind.

"All they've really shown in this particular study is there's citrulline in the rind," Rae told the Sun-News Wednesday. "There is absolutely no study in which citrulline has resulted in more erections."

Laura Watson of Watson Gardens in San Miguel, which grows a variety of red, yellow and orange watermelon, said Wednesday at the downtown farmer's market in Las Cruces that she was skeptical of the alleged Viagra effect: "Who'd want to eat the rinds anyway?"

Jason Nicoll, who was also at the farmer's market selling an early crop of watermelon from his farm west of Deming, said he didn't know if the connection was true, "but it sounds like a good marketing tool."

Alamogordo resident Allen Leadingham, 50, the youth services director at WSMR, was more amused by the possibility.

"It seems much more natural than Viagra, the chemical, and probably explains why I like watermelon so much," said Leadingham, who said he predicted the summer treat would be "much more of a staple around the house."

Whether the possibility of a link will turn out to bear fruit is yet to be seen. Dr. Ferid Murad, who shared a Nobel Prize in 1998 for his research on nitric oxide, including identifying its role in nitroglycerin, told the Washington Post in 2003 that citrulline "acts only marginally in recycling L-arginine" to increase nitric oxide.

Viagra works by allowing nitric oxide to relax blood vessels. It does so by blocking an enzyme that inhibits the production of nitric oxide by a second enzyme. The production of nitric oxide is carried out by a third enzyme, a reaction that needs oxygen and arginine, which is available in many foods and as a dietary supplement.

"Eventually, that causes the cell to relax, which allows the (erectile tissue) in the penis to relax and fill with blood, which causes erection ... But that's like 47 steps down the road," Rae said. "That's like saying because SSRIs (selective serotonin reuptake inhibitors), Prozac and stuff, work on serotonin and serotonin is produced using vitamin B6, that taking vitamin B6 is like taking an SSRI."

Rae says there's no evidence that popping extra arginine will produce more erections either, unless your diet is extremely low in protein.

"There's no evidence that even feeding people arginine produces an erection," Rae said. "So going a step backwards and saying citrulline will produce them is just silly guesswork, until they provide some evidence that it really does so. And then to say that's the same mechanism as Viagra is just sillier still."

"If you're worried about arginine," Rae said, "just make sure you get enough protein in your diet. Certainly, don't bother gorging on watermelon rind!"


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