Aphrodisiac properties of Tribulus Terrestris extract (Protodioscin) in normal and castrated rats
Introduction
The role of androgens in sexuality is unequivocal. Embryonic differentiation of the fetus into a male and its subsequent growth along this line is essentially due to the presence of physiological amounts of androgens (especially testosterone and its metabolite dihydrotestosterone) in the body [1]. Apart from these two major androgens, dehydroepiandrosterone secreted from the adrenals also contribute significantly to the overall androgenic status and therefore influence the sexual characteristics [2]. Reduction in the levels of these steroids (hypogonadism) at the early developmental phase leads to structural abnormalities of the penis [3], [4]. Hypogonadism in adulthood may result in loss of libido and sexual activity and androgen replacement has been found to be effective in restoration of these conditions [5], [6], [7], [8]. Androgens contribute to penile erection by acting in concert with the other determinants of penile erectile physiology. Androgen receptors mediate the effects of androgens and their presence in various tissues has been demonstrated [9], [10], [11]. Using the rat model it has been demonstrated previously that sexual behaviour and erection are androgen dependent (acting both centrally and peripherally) and that treatment with testosterone of the castrated rats helped in restoration of both sexual behaviour and penile erectile capacity [3], [6], [12]. It has also been demonstrated by various studies that androgens regulate corporal nitric oxide synthase (NOS) activity [13], [14], [15].
The aphrodisiac properties of Tribulus terrestris extract (TT) that contains protodioscin (PTN), a steroidal saponin that forms 45% (dry weight) of the extract was explored in castrated rats. The plant TT or its products have been extensively used both in the Chinese and Indian traditional medicine for the treatment of various ailments such as urinary, cardiovascular, and gastrointestinal disorders [16], [17], [18]. Administration of TT to humans and animals improves libido and spermatogenesis [19]. PTN is also found to increase the levels of testosterone, leutinizing hormone [20], dehydroepiandrosterone [21], dihydrotestosterone and dehydroepiandrosterone sulphate [22]. The corpus cavernosal tissues obtained from New Zealand White rabbits following treatment with TT were tested in vitro with various pharmacological agents and electrical field stimulation and was found to have a proerectile effect [23]. The present study was carried out to further understand the androgen releasing property of the TT extract (PTN) and its relation to sexual behaviour and intracavernous pressure (ICP) using castrated rats.
Section snippets
Materials and methods
Forty adult male Sprague-Dawley (SD) rats approximately 6 weeks old and weighing between 200–250 g were fed on standard rat pellets (Glen Forest Stock Feeders, Western Australia) and water ad libitum. The animals were housed under standard laboratory conditions and maintained on a reverse light- dark cycle (10 PM–10 AM) for a minimum of two weeks prior to the study to facilitate adaptation. The rats were divided into five experimental groups of 8 each. Of these, two groups were intact and three
Body and prostate weight
Considerable decreases in both the body weight (by 11.80%, 6.09% and 9.63%) and prostate weight (by 41.29%, 8.04% and 26.70%) for the groups III, IV and V respectively were observed among the castrated groups of rats compared to the intact group. These parameters were statistically significant. Within the castrated group the increase in prostate weight (by 43.28% and 29.85% for group IV and V respectively) were statistically significant compared to the castrated control (Table 1).
Sexual behaviour
The rats from
Discussion and conclusion
Animal studies from various centres indicate that sexuality decreases with low androgenic status and is restored following androgen replacement. In this current study we attempted to investigate the effect of TT using the castrated rat, a convenient model for studying the effect of androgens in relation to the sexual characteristics [3]. In this study the overall sexual behaviour parameters were markedly reduced among the castrated groups of rats compared to the intact group. Castration leads
Acknowledgements
We would like to thank Sopharma Joint Stock Co., Bulgaria, for providing the Tribulus terrestris extract used in this study.
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