This study examined the effect of aqueous extract of Arctium lappa L. roots on male sexual competence in rats, with viagra as a positive reference drug. To the best of our knowledge, this is the first study to report the effects of aqueous extract of Arctium lappa L. roots in male rodents. Arctium lappa L. root extract enhanced the sexual behavior of male rats compared with controls administered DW. These results scientifically support the use of Arctium lappa L. roots for enhancing male sexual ability.
The mating behavior test revealed that aqueous extract of Arctium lappa
L. roots significantly increased MF and IF, compared with the control group, though the effect was less than that of Viagra. Aqueous extract of Arctium lappa
L. roots also caused significant reductions in ML and IL, compared with control animals, while highly significant decreases in ML and IL were observed in animals treated with Viagra. MF and IF are considered to be indices of libido (sexual desire) and potency, while ML and IL are also indicators of sexual arousal. The significant increases in MF and IF and the decreases in ML and IL indicate that libido and potency were enhanced by Arctium lappa
L. root extract [28
]. Furthermore, the prolongation of EL by aqueous extract of Arctium lappa
L. roots is an indicator of prolonged duration of coitus. PEI is considered to be an index of potency, libido, and the rate of recovery from exhaustion after the first series of mating. The decreased PEI observed with various doses of plant extract may have been the result of enhanced potency and libido, and/or reduced exhaustion in the first series of matings. These observations all further support the role of Arctium lappa
L. root extract in improving sexual function.
The penile erection index is important for evaluating the effect of drug administration on erectile function [32
]. The potency test showed that the extract significantly increased the frequency of all components of the penile reflex compared with the control group, but to a lesser degree than Viagra. This indicates that the aqueous extract of Arctium lappa
L. roots also increases potency. Treatment with all three doses of aqueous extract of Arctium lappa
L. roots remarkably delayed EL, with no negative effect on the other parameters of sexual behavior, and with no locomotor alterations throughout the observation period. The delayed EL and increased penile erection in treated male rats indicated the involvement of NO in the intervention [33
]. The use of this plant during labor by Native Americans suggests an oxytocic effect of the plant's biologically active components. Oxytocin is known to be a potent facilitator of copulatory behavior in male rats, centered on ejaculatory function [34
]. Oxytocin administration has been shown to affect the consummatory components of masculine sexual behavior by lowering the ejaculatory threshold and dramatically reducing EL [35
]. However, the physiological mechanism responsible for the involvement of the oxytocinergic system in promotion of sexual potency by the extract cannot be identified based on the results of the current study.
The continued administration of various concentrations of Arctium lappa
L. roots extract for 15 days increased hormone levels. The mean testosterone level in untreated males was 2.27 ng/mL, and this was significantly increased to 5.18 ng/ml in the group treated with the highest dose of extract (p
< 0.01). Administration of extract increased testosterone, indicating the involvement of the stimulation of hypothalamic-pituitary-gonadal axis, the increase in testosterone might have been caused by the enhancement in the GnRH-LH signalling [36
]. Testosterone is the main male gonadal hormone produced by the interstitial Leydig cells of the testis. In the testes, Luteinizing hormone (LH), a gonadotrophin, which binds to receptors on Leydig cells, stimulating synthesis and secretion of testosterone. Administration of extract increased testosterone could thus be assumed that some phytoconstituent present in the extract may possibly mimic the function of LH to stimulate interstitial cells. In the complex mechanism that regulates copulatory behavior, an increase in testosterone level has been associated with a moderate but significant increase in sexual desire and libido [37
]. Penile tumescence and rigidity, as well as the accessory muscles that help to provide additional penile rigidity and ejaculation, depend on testosterone for normal sexual activity [40
]. Testosterone may also facilitate male sexual behavior by increasing dopamine release in the medial preoptic area and potentiating nitrergic neurotransmission [41
]. Increased serum testosterone levels after administration of Arctium lappa
L. roots extract could thus be considered as one of the contributing factors responsible for the overall increased sexual performance in the treated groups, especially for the lengthening of EL and increased copulatory ability in rats. Overall, these results suggest that Arctium lappa
L. roots extract might represent an interesting alternative to serotonergic antidepressants for the treatment of PE.
Studies in laboratory animals have implicated many components of plant extracts as possible bioactive agents responsible for increasing endogenous testosterone levels and enhancing male sexual behavior. These include steroids and steroidal saponins, which may act as intermediaries in the steroidal pathway of androgen production. Saponins may bind to hormone receptors, resulting in conformational changes that can enhance the physiological functions of the hormone, or can bind to enzymes involved in the synthesis of such hormones, thus enhancing their production [43
]. In addition, flavonoids have been implicated in altering androgen levels and may also be responsible for enhancing male sexual behavior by enhancing testosterone synthesis or by preventing its metabolic degradation [45
In addition to increasing the biosynthesis and secretion of androgens, many bioactive components of plant extracts also exhibit aphrodisiac activities by acting directly on the central nervous system to modulate the action of neurotransmitters and gonadal tissues in males, or through vasodilation and the generation of NO, which can also change sexual behavior. Alkaloids increase the dilation of blood vessels in the sexual organs [20
]. Ginseng saponin has been shown to enhance libido and copulatory performance by acting directly on the central nervous system and gonadal tissues [48
], and evidence suggests that it can facilitate penile erection by directly inducing the vasodilatation and relaxation of the penile corpus cavernosum via an NO-dependent mechanism [49
Phytochemical studies indicate that Arctium lappa
L. root contains sterols, flavonoids, phenols, saponins, lignans (such as arctiin), alkaloids, sugars (polysaccharides), vitamins, tannin, minerals, lactone, polyacetylenes and amino acids [21
]. The improvements in sexual function demonstrated in the current study might thus be due to the presence of such compounds in Arctium lappa
L. root extracts. Further studies are required to identify the active constituent(s) responsible for the sexual function improvement activities and the mechanisms whereby these activities are implemented. The results of the current study suggest that aqueous extract of Arctium lappa
L. roots may be a promising new agent for the clinical treatment of MSD.