Epimedium

Taxobox
name = "Epimedium"

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image_width = 240px
image_caption = "Epimedium grandiflorum"
regnum = Plantae
divisio = Magnoliophyta
classis = Magnoliopsida
ordo = Ranunculales
familia = Berberidaceae
genus = "Epimedium"
genus_authority = L.
subdivision_ranks = Species
subdivision = About 60 species in cultivation, including: "Epimedium acuminatum" "Epimedium alpinum" "Epimedium brachyrrhizum" "Epimedium brevicornum" "Epimedium campanulatum" "Epimedium chlorandrum" "Epimedium davidii" "Epimedium diphyllum" "Epimedium dolichostemon" "Epimedium ecalcaratum" "Epimedium elongatum" "Epimedium epsteinii" "Epimedium fangii" "Epimedium flavum" "Epimedium franchetii" "Epimedium grandiflorum" "Epimedium ilicifolium" "Epimedium latisepalum" "Epimedium leptorrhizum" "Epimedium lishihchenii" "Epimedium membranaceum" "Epimedium mikinorii" "Epimedium myrianthum" "Epimedium ogisui" "Epimedium pauciflorum" "Epimedium perralderianum" "Epimedium platypetalum" "Epimedium pinnatum" "Epimedium pubescens" "Epimedium pubigerum" "Epimedium rhizomatosum" "Epimedium sagittatum" "Epimedium sempervirens" "Epimedium setosum" "Epimedium sutchuenense" "Epimedium truncatum" "Epimedium wushanense"

"Epimedium", also known as Barrenwort, Bishop's Hat, Fairy Wings, Horny Goat Weed, or Yin Yang Huo ( _zh. 淫羊藿), is a genus of about 60 or more species of herbaceous flowering plants in the family Berberidaceae. The large majority are endemic to southern China, with further outposts in Europe, and central, southern and eastern Asia.

"Epimedium" species are hardy perennials. The majority have four-petaled "spider-like" flowers in spring. Many are believed to be aphrodisiacs, particularly horny goat weed, which has shown promising signs of becoming a genuine alternative to Viagra for impotent men. [cite web|url=http://www.meeja.com.au/index.php?display_article_id=291|title=Horny Goat Weed may offer Viagra alternative |publisher=www.meeja.com.au |date=2008-09-30 |accessdate=2008-09-30 ]

Aphrodisiac

Many species of "Epimedium" are alleged to have aphrodisiac qualities. According to legend, this property was discovered by a Chinese goat herder who noticed sexual activity in his flock after they ate the weed. It is sold as a health supplement; usually in raw herb, tablet, or capsule form and sometimes blended with other supplements. The over-exploitation of wild populations of "Epimedium" for use in traditional Chinese medicine is having potentially serious consequences for the long-term survival of several species, none of which are widely cultivated for medicinal purposes.

The "active ingredient" in Epimedium is icariin [ [http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=5318997 PubChem Entry for Icariin.] ] , which can be found in standardized extracts from 5% up to 60% potent. Strengths above that are usually reserved for lab use.

Icariin is purported to work by increasing levels of nitric oxide, which relax smooth muscle. It has been demonstrated to relax rabbit penile tissue by nitric oxide and PDE-5 activity. [Chiu JH, Chen KK, Chien TM et al. "Epimedium brevicornum Maxim extract relaxes rabbit corpus cavernosum through multitargets on nitric oxide/cyclic guanosine monophosphate signaling pathway". Int J Impot Res. 2006;18:335-42. PMID 16395327] Other research has demonstrated that injections of Epimedium extract directly into the penis of the rat results in an increase in penile blood pressure. [Chen KK, Chiu JH. "Effect of Epimedium brevicornum Maxim extract on elicitation of penile erection in the rat." Urology. 2006;67:631-5. PMID 16527595]

Like sildenafil ("Viagra"), icariin, the active compound in Epimedium, inhibits the activity of PDE-5. "In vitro" assays have demonstrated that icariin inhibits PDE-5 with an IC₅₀ of around 1 micromolar, [Ning H, Xin ZC, Lin G et al. "Effects of icariin on phosphodiesterase-5 activity in vitro and cyclic guanosine monophosphate level in cavernous smooth muscle cells." Urology 2006;68:1350-4. PMID 17169663] [Xin ZC, Kim EK, Lin CS et al. "Effects of icariin on cGMP-specific PDE5 and cAMP-specific PDE4 activities." Asian J Androl. 2003;5:15-8. PMID 12646997] while sildenafil has an IC₅₀ of about 6.6 nanomolar (.0066 micromolar) and vardenafil ("Levitra") has an IC₅₀ of about 0.7 nanomolar (.0007 micromolar). [Saenz de Tejada I, Angulo J, Cuevas P et al. "The phosphodiesterase inhibitory selectivity and the in vitro and in vivo potency of the new PDE5 inhibitor vardenafil." Int J Impot Res. 2001;13:282-90. PMID 12646997] Measured differently, the EC₅₀ of icariin is approximately 4.62 micromolar, while sildenafil's is .42 micromolar. [Jiang Z, Hu B, Wang J et al. "Effect of icariin on cyclic GMP levels and on the mRNA expression of cGMP-binding cGMP-specific phosphodiesterase (PDE5) in penile cavernosum." J Huazhong Univ Sci Technolog Med Sci. 2006;26:460-2. PMID 17120748] The amount of oral administration of Epidemium extract necessary to achieve these relative concentrations is unclear from the literature.

A recently published Italian study modified icariin structurally and investigated a number of derivatives. [Dell'Agli M, Galli GV, Dal Cero E et al. [http://dx.doi.org/10.1021/np800049y "Potent Inhibition of Human Phosphodiesterase-5 by Icariin Derivatives."] J Nat Prod. 2008;71 Sep 9. [Epub ahead of print] . PMID 18778098] Inhibitory concentrations for PDE-5 close to sildenafil could be reached. Moreover, the most potent PDE-5 inhibitor of this series was also found to be a less potent inhibitor of phosphodiesterase-6 (PDE-6) and cyclic adenosine monophosphate-phosphodiesterase (cAMP-PDE), thus showing it to have more specificity for PDE-5 than sildenafil.

Epimedium has been shown to up-regulate genes associated with nitric oxide production and changes in adenosine/guanine monophosphate balance in ways that other PDE5 inhibitors do not.

Cultivation

Some varieties and hybrids have been in Western cultivation for the last 100 to 150 years. There is now a wide array of new Chinese species, many of which are only recently discovered, and a number of which have yet to be named. There are also Japanese hybrids and forms that are now arriving in the west, extending the boundaries of the genus in cultivation. The majority of the Chinese species have not been fully tested for hardiness or indeed for any other aspect of their culture. The initial assumption that the plants would only thrive where their native conditions could be closely replicated have proven to be overly cautious, as most varieties are proving extraordinarily amenable to general garden and container cultivation.

Whilst they can be successfully propagated in early spring, "Epimedium" are best divided in late August, with the aim of promoting rapid re-growth of roots and shoots before the onset of winter. Several breeders (in particular Darrell Probst, Tim Branney & Robin White) have also undertaken their own hybridization programmes with the genus "Epimedium". Various new nursery selections are gradually appearing in the nursery trade, the best of which are extending the colour and shape range of the flowers available to the gardener.

Literature

* [http://www.heronswood.com/epimedium-culture/ Epimedium Care and Culture] (Heronswood Nursery)
* William T. Stearn, "The Genus Epimedium", revised edition 2002, ISBN 0-88192-543-8

References