Turnera diffusa Wild (Turneraceae) recovers sexual behavior in sexually exhausted males
Introduction
Sexual dysfunction has been associated to a decrease in quality of life, hence a growing number of drugs or compounds have been used as treatments (Bancroft and Janssen, 2000). Medicinal plants that are reputed to be aphrodisiacs, such as Turnera diffusa Wild (Turnera diffusa, Turneraceae), are considered as an alternative treatment to enhance sexual performance in subjects with sexual dysfunction. Turnera diffusa is a native Mexican shrub that grows in dry places and its cultivation was initiated recently in Baja California, Mexico. It has a history of being used by Indian groups in Northern Mexico and is known as “Damiana de Guerrero”, “pastorcita”, “hierba del pastor”, “hierba del venado” and the most common name is “Damiana de California”. It has been traditionally prescribed as a leaf decoction against muscle and nerve weakness, as an aphrodisiac, a tonic and for catarrhal and bladder inflammations (Linares et al., 1999, Schultes and Hoffmann, 2000).
The reputation of Turnera diffusa as an aphrodisiac is wide and multiple products containing it are offered in the market (Linares et al., 1999); however, there are very few controlled studies that confirm such properties on sexual performance. In 1999, Arletti and co-workers reported that the aqueous extract of Turnera diffusa facilitated sexual behavior in so-called “sexually sluggish” male rats, considered a natural model of sexual dysfunction (Waldinger and Olivier, 2005). Sluggish rats showed slow and irregular copulation, an increased number of mounts and intromissions preceding ejaculation and a variable ejaculation latency. Interestingly, Turnera diffusa changed this copulatory pattern to a more efficient one, i.e. reducing ejaculation latency (Arletti et al., 1999). At the moment, it is unkown whether Turnera diffusa affects other forms of male sexual inhibition, such as sexual exhaustion.
Sexual exhaustion (SExh) is a phenomenon that appears after sustained copulation with a single female. The main feature of this phenomenon is the natural instatement of a long-lasting inhibition of sexual behavior (Beach and Jordan, 1956, Larsson, 1956, Fernández-Guasti and Rodríguez-Manzo, 2003). Using a protocol of 4 h ad libitum copulation, male rats can accomplish several ejaculatory series (described as all the events from the first intromission to ejaculation) and gradually reduce their copulatory activity. Thus, the criterion of SExh is achieved after a 90-min period elapses without expression of sexual behavior (Rodríguez-Manzo and Fernández-Guasti, 1994). Twenty-four hours after repeated mating behavior, SExh is expressed in two different forms: 2/3 of the population shows a complete inhibition of sexual behavior, while 1/3 of the population executes one ejaculatory series without resuming copulation afterwards (Rodríguez-Manzo and Fernández-Guasti, 1994, Rodríguez-Manzo and Fernández-Guasti, 1995a). Neurochemical and pharmacological studies have suggested that changes in the concentration of several neurotransmitters could underlie the sexual inhibition diplayed by SExh animals (Mas et al., 1995, Fiorino et al., 1997, Rodríguez-Manzo et al., 2002).
Sexual refractoriness due to SExh can be observed even 7 days after (Fernández-Guasti and Rodríguez-Manzo, 2003) and it has been presumed that long-lasting plastic changes are needed to recover sexual behavior (Martínez-Mota et al., 2005). Drugs affecting different neurotransmiter systems, such as the serotonergic (i.e., the 5-HT1A agonist 8-OH-DPAT), noradrenergic (i.e., the α2-adrenergic antagonist yohimbine), opioidergic (i.e., the opioid antagonists naloxone and naltrexone) and dopaminergic systems (i.e. apomorphine) can restore copulatory behavior in SExh males within minutes (Fernández-Guasti and Rodríguez-Manzo, 2003, Rodríguez-Manzo and Fernández-Guasti, 1994, Rodríguez-Manzo and Fernández-Guasti, 1995a, Rodríguez-Manzo and Fernández-Guasti, 1995b). It has been claimed that features of the SExh model are in agreement with sexual dysfunction in humans, which may be caused by altered excitatory and inhibitory transmission (Bancrof, 1999).
On this basis, the objective of the present study was to determine whether the aqueous extract of Turnera diffusa recovers sexual behavior in male rats displaying sexual inhibition resulting from repeated ejaculation (SExh model). The effect of Turnera diffusa was compared with a reference drug, the α2-adrenergic antagonist yohimbine, which has been reported to reverse the SExh state (Rodríguez-Manzo and Fernández-Guasti, 1994). In order to discard unspecific effects of Turnera diffusa the animals were also evaluated in an open field and in anxiety tests. In addition, an HPLC–ESI-MS analysis was carried out to identify the main components in the Turnera diffusa active aqueous extract.
Section snippets
Animals
Male (220–350 g body weight) and female (200 g body weight) Wistar rats were obtained from the vivarium of the Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz. The animals were housed, five per cage (53 cm × 43 cm × 20 cm), in a room under inverted light:dark conditions (12:12 h, lights on at 22:00 h) and with free access to water and commercial rat chow. Animal management was done in agreement with the general principles of laboratory animal care (NIH publication # 85-23, revised in 1985) and
Behavioral tests
Fig. 1 illustrates the effect of Turnera diffusa on the percentage of SExh animals copulating in a 30-min sexual behavior test. As expected, 24 h after ad libitum copulation SExh males of the control group exhibited characteristic features: a reduced percentage (36.36%) of rats showed mounts, intromissions and achieved one ejaculation and none resumed copulation, while the complementary proportion of SExh males was unable to express any sexual behavior at all. Turnera diffusa at the highest dose
Discussion and conclusions
This is the first study demonstrating that a single administration of the aqueous extract of Turnera diffusa recovers copulation in male rats with a long-lasting inhibition of sexual behavior induced by repeated ejaculation (SExh paradigm). The main effects of Turnera diffusa on the recovery of male sexual behavior were comparable to actions of yohimbine, an α2-adrenergic antagonist used in the present study as a reference drug. The chemical analysis showed the presence of caffeine, arbutine
Acknowledgements
We wish to thank Dr. Bryan Phillips Farfán for the review of manuscript, and Ms. Carmen Marquez Alonso, Ms. Eréndira García Rios and Mr. Sergio Márquez Baltazar for technical assistance. This work was partially supported by grant 62020 from the “Consejo Nacional de Ciencia y Tecnología”.
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