Tribulus: Background. Actions

2010

Common Name

Tribulus

Other Names

Al-gutub, cats-head, devil’s-thorn, devil’s-weed, goathead, puncture vine, qutiba

Botanical Name / Family

Tribulus terrestris (family Zygophyllaceae)

Plant Parts Used

Leaf

Chemical Components

Different parts of the plant contain different constituents in varying ratios. Overall, the steroidal saponin content is considered the most important and includes constituents such as protodioscin, diosgenin, yamogenin, epismilagenin, tigogenin, neotigogenin, gitogenin and neogitogenin. Two additional steroidal saponins, terrestrinins A (1) and B (2), have recently been isolated in 80% ethanol from the fruit. The significance of this has not yet been determined. Beta-sitosterol, vitamin C, potassium and calcium are also found in the herb. Two major alkaloids have been identified: harmane and norharmane.

Of the steroidal saponins, protodioscin is considered the chief constituent responsible for the plant’s effects on libido and sexual functioning. Preliminary observations suggest that Tribulus terrestris grown in different soils does not consistently produce this constituent and considerable variations have been identified in commercial products.

Steroidal saponins consist of a furostanol- or spirostanol-based aglycone and an oligosaccharide attached to a steroid nucleus. Steroidal saponins are very common in the plant kingdom and are natural components in many foods, such as asparagus, garlic and oats.

Historical Note

Widely distributed in the Mediterranean region, Middle East and southern Africa, tribulus is an important plant used in traditional Ayurvedic, Arabic and Chinese medicine. Different parts of the tribulus plant are used to treat a variety of conditions, such as cough, colicky spasms, diarrhoea, cardiovascular disease, various kidney disorders, including kidney stones, and as an insect repellent.

Tribulus:  Main Actions

Tribulus has not undergone significant clinical investigation; therefore, evidence of activity primarily derives from animal and in vitro studies. Additionally, some studies have investigated the pharmacological effects of the isolated saponin content.

INCREASES LIBIDO AND ENHANCES SEXUAL FUNCTION

The exact mechanism by which tribulus influences sexual behaviour is not known, but increasing androgenic status and NO release appear to be chiefly responsible. More specifically, some reports have suggested increases in dehydroepiandrosterone (DHEA) and testosterone are possible.

The constituent protodioscin is considered the most important in this regard and is converted to DHEA. Additionally, ex vivo tests have observed pro-erectile effects with protodioscin due to increased release of NO from the endothelium and nitronergic nerve endings.

DIURETIC

A large oral dose of 5 g/kg tribulus was shown to have greater diuretic activity than frusemide 120 mg/kg in a recent animal study.

KIDNEY STONE PREVENTION

With regard to kidney stones, tribulus has been found to decrease the amount of urinary oxalate in rats and produce significant dose-dependent protection against experimentally induced uroliths in animal studies. A recent in vitro study using human urine suggests that the diuretic properties of tribulus may be the most crucial mechanism for preventing urinary stone.

Tribulus:  Other Actions

A Chinese report of successful treatment of angina pectoris with the saponin content of tribulus suggests that the preparation dilates coronary arteries and improves coronary circulation.

In another study 10 mg/kg/day of the aqueous extract of the fruit has shown antihypertensive effects in an animal trial when compared to control. The authors concluded that effects are possibly due to inhibition of ACE activity.

Experiments with healthy mice have found Tribulus terrestris significantly inhibits gluconeogenesis and influences glycometabolism and reduces triglyceride and total cholesterol levels.

A dose-dependent antispasmodic activity causing a significant decrease in peristaltic movements has been demonstrated with the isolated saponin content of tribulus.

More recently, an in vitro test has also identified COX-2 inhibition activity, suggesting possible anti-inflammatory actions.

Two isolated constituents tribulosin and beta-sitosterol-d-glucoside have shown anthelmintic activity in vitro against Caenorhabditis elegans.

Of eight steroid saponins tested, two showed potent antifungal activity against Candida albicans, with one, TTS-12, demonstrating its ability to decrease virulence and destroy the cell membrane.