Effects of Tribulus terrestris on endocrine sensitive organs in male and female Wistar rats (original) (raw)

Abstract

Aim of the study

Investigate the possible effects of Tribulus terrestris (TT) on endocrine sensitive organs in intact and castrated male rats as well as in a post-menopausal rat model using ovariectomized females.

Materials and methods

Three different dose levels of TT (11, 42 and 110

mg/kg/day) were administered to castrated males for 7 days and to intact males and castrated females for 28 days. In addition to TT treatment, all experiments also included a group of rats treated with dehydroepiandrosterone (DHEA). In experiments using castrated males and females we also used testosterone and 17α-ethynylestradiol, respectively, as positive controls for androgenicity and estrogenicity.

Results

Neither DHEA nor TT was able to stimulate androgen sensitive tissues like the prostate and seminal vesicle in both intact and castrated male rats. In addition, administration of TT to intact male rats for 28 days did not change serum testosterone levels as well as did not produce any quantitative change in the fecal excretion of androgenic metabolites. However, a slight increase in the number of homogenization-resistant spermatids was observed in rats treated with 11

mg/kg/day of TT extract. In ovariectomized females, TT did not produce any stimulatory effects in uterine and vaginal epithelia.

Conclusions

Tribulus terrestris was not able to stimulate endocrine sensitive tissues such as the prostate, seminal vesicle, uterus and vagina in Wistar rats, indicating lack of androgenic and estrogenic activity in vivo. We also showed a positive effect of TT administration on rat sperm production, associated with unchanged levels of circulating androgens.

Introduction

Tribulus terrestris L. (Zygophyllaceae) is a perennial creeping herb with a widespread distribution in Mediterranean, subtropical and desert climates worldwide. In traditional folk medicine, it has been used since ancient times as an aphrodisiac as well as to treat urinary infections, inflammation, oedema and other ailments (Adaikan et al., 2001).

Although experimental and clinical studies have partially confirmed some effects of Tribulus terrestris (TT) on libido and sperm production, there is still much debate regarding possible mechanisms of action as well as therapeutic applications. Results published by Gauthaman et al., 2002, Gauthaman et al., 2003 indicate that TT can improve some aspects of male sexual behaviour and enhance spermatogenesis in rats. In addition, there are clinical data indicating stimulatory effects of TT on sperm quantity and quality and improved sexual response in men (Arsyad, 1996). Reports of increased androgen levels have also been reported following TT administration to nonhuman primates, rats and rabbits (El-Tantawy et al., 2007, Gauthaman and Ganesan, 2008), but most of these effects were short-lived and showed no clear dose–response relationships. In addition, there is no consensus on the exact mechanisms underlying TT effects on sexual performance and spermatogenesis. It is believed that the steroidal saponins present in TT extracts, particularly protodioscin, can increase endogenous androgen production by increasing luteinizing hormone (LH) release from the pituitary gland. Alternatively, it has been proposed that TT active components might be enzymatically converted into weak androgens like dehydroepiandrosterone (DHEA), which could in turn be converted into more potent androgens like testosterone in the gonads and peripheral tissues (Adaikan et al., 2001). However, changes in endogenous hormone levels following TT administration are still controversial (Neychev and Mitev, 2005).

The presence of steroidal saponins also raises the question whether TT extracts might have intrinsic hormonal activity that could directly stimulate male and/or female endocrine sensitive tissues such as the prostate, seminal vesicle, uterus and vagina (Nian et al., 2006). This is considered an important issue for both efficacy and safety assessment of TT. Gauthaman et al. (2002) reported that administration of TT to castrated rats was able to improve sexual behaviour and increase prostate weight and intracavernous pressure in relation to castrated controls. Currently, TT has been also indicated as an alternative treatment to hormone replacement therapy in aging men and women. In the present study, we investigated whether TT extract could affect endocrine sensitive organs in intact and castrated male rats as well as in a post-menopausal rat model using ovariectomized females. Moreover, we also investigated the effects of TT on sperm production and monitored fecal androgen levels in intact treated males. In addition to TT treatment, all experiments also included a group of rats treated with DHEA, an endogenous hormone claimed to directly and/or indirectly increase androgen effects and promote general well being in aging men and women (Brown et al., 2000, Brown et al., 2001).

Section snippets

Tribulus terrestris extract

The dry ethanolic extract of TT (Androsten®) was supplied by Herbarium Laboratório Botânico (Colombo, Brazil; lot number 047918) and contained 16.43% of protodioscin. A dried voucher specimen is also available.

Animals

Wistar rats were obtained from the stock of the Universidade Federal do Paraná and kept under a 12

h light/dark cycle and controlled temperature (22

°C). Standard pellet food (Nuvital®, Curitiba/PR) and tap water were available ad libitum. All experimental protocols were approved by the

Test of androgenicity using castrated males – Hershberger Assay

An increase in both ventral prostate and seminal vesicle relative weights was seen in castrated rats treated with 0.25

mg/kg/day testosterone propionate, when compared to castrated controls. However, no significant effects were seen in rats treated with TT or DHEA (Fig. 1).

Evaluation of TT effects in intact male rats

At the end of treatment, no changes were observed in serum testosterone levels at any experimental group (Fig. 2). However, fecal androgenic metabolites were increased in the group treated with DHEA in all time points

Discussion

Tribulus terrestris (TT) has been popularly used as an aphrodisiac and enhancer of sperm production and more recently as an alternative to hormone replacement therapy in aging men and women (Gauthaman and Ganesan, 2008). In the present study, we demonstrated that TT has no intrinsic hormonal activity, being unable to stimulate endocrine sensitive organs in both male and female rats. We also demonstrated that administration of TT to intact male rats for 28 days did not change serum testosterone