Watermelon: A Natural Viagra?

Watermelon: A Natural Viagra?:

Watermelon may work as a natural Viagra. That's because watermelon is rich in an amino acid called citrulline, and relaxes and dilates blood vessels much like Viagra and other drugs meant to treat erectile dysfunction.

"We have known that watermelon has citrulline," says Bhimu Patil, PHD, director of the Fruit and Vegetable Improvement Center at Texas A&M University, College Station. Until recently, he tells WebMD, scientists thought most of the citrulline was in the watermelon rind. "Watermelon has more citrulline in the edible part than previously believed," he says.

How could watermelon be a natural Viagra? The amino acid citrulline is converted into the amino acid arginine. Arginine is a precursor for nitric oxide, and the nitric oxide regulate the blood vessel dilation.

Watermelon consumption increases plasma arginine concentrations in adults:

"The increased blood concentrations of arginine and ornithine and stable concentrations of plasma citrulline in response to watermelon consumption indicated that the citrulline from this plant origin was effectively converted into arginine. These results demonstrate that plasma concentration of arginine can be increased through intake of citrulline from watermelon."

Lignans from the roots of stinging nettle (Urtica dioica) and their metabolites bind to human sex hormone binding globulin (SHBG)

Lignans from the roots of Urtica dioica and their metabolites bind to human sex hormone binding globulin (SHBG)

Testosterone and estradiol circulate in the bloodstream, bound mostly to SHBG and to some degree bound to serum albumin. Only a small fraction is unbound, or "free," and thus biologically active and able to enter a cell and activate its receptor. The SHBG inhibits the function of these hormones. Thus bioavailability of sex hormones is influenced by the level of SHBG.(http://en.wikipedia.org/wiki/Sex_hormone-binding_globulin)

Résumé / Abstract
Polar extracts of the stinging nettle (Urtica dioica L.) roots contain the lignans (+)-neoolivil, (-)-secoisolariciresinol, dehydrodiconiferyl alcohol, isolariciresinol, pinoresinol, and 3,4-divanillyltetrahydrofuran. These compounds were either isolated from Urtica roots, or obtained semisynthetically. Their affinity to human sex hormone binding globulin (SHBG) was tested in an in vitro assay. In addition, the main intestinal transformation products of plant lignans in humans, enterodiol and enterolactone, together with enterofuran were checked for their activity. All lignans except (-)-pinoresinol developed a binding affinity to SHBG in the in vitro assay. The affinity of (-)-3,4-divanillyltetrahydrofuran was outstandingly high. These findings are discussed with respect to potential beneficial effects of plant lignans on benign prostatic hyperplasia (BPH).