ED 10. The effect and mechanism of action of tribulus terrestris extract on penile erection

Tribulus terrestris has been popularly used as an aphrodisiac as well as to treat urinary infections and inflammation. Little is known about the effects and action mechanism of Tribulus terrestris on penile erection. Therefore, the effect of Tribulus terrestris extract and the action mechanism of Tribulus terrestris extract on relaxation of the corpus cavernosum (CC) were investigated. And also, erectogenic effects of oral administration of this extract were assessed. New Zealand white male rabbit weighing 2.5-3.0 kg and Sprague-Dawley male rats weighing 280-320 g were used. The relaxation effects and the action mechanism of Tribulus terrestris extract on the rabbit CC were investigated in organ bath. In order to evaluate whether the relaxation response of the CC shown in an organ bath occurs in vivo or not, intracavernous pressure (ICP) was calculated after oral administration every day for a month. Additionally, cAMP and cGMP in the CC were measured using immunoassay. Tension was measured with isometric force transducers, and smooth muscle relaxation was expressed as the percent decrease in precontraction induced by phenylephrine. ICP/mean arterial pressure (MAP) was assessed in rats after the oral administration of mixture of both extract for one month, and changes in cGMP and cAMP concentrations were measured based on the mixture of both extract concentration. Tribulus terrestris extract showed concentration-dependent relaxation effects of the CC in the organ bath study. Relaxation of CC by the Tribulus terrestris extract was inhibited in both endothelium-removed group and L-NAME pretreatment group. ICP measured after oral administration of the Tribulus terrestris extract for a month was higher than that measured in the control group and significant increase in cAMP was also observed in the Tribulus terrestris extract group.

The relaxation effect of Tribulus terrestris extract on the CC in an organ bath showed concentration-dependent relaxation. The mechanism was a reaction involving NO/NOS pathway in the endothelium of CC. Moreover, vivo study after the onemonth oral administration of Tribulus terrestris extract showed significant concentration dependent increase of ICP compared with the control group. Accordingly, the Tribulus terrestris extract is considered to show satisfactory effects for ED in the clinical treatment.