Thus, treatment options such as penile prostheses, psychosexual and oral therapies are implemented to remedy this problem (Porst, 2002; Meuleman, 2003). There has been considerable progress in research over the last few decades in the medical management of ED, and oral treatments are nowadays the most widely used, particularly in addition to the discovery of phosphodiesterase type 5 (PDE5) inhibitors such as Sildenafil, Tadalafil or Vardenafil, the use of α 2-adrenergic receptor antagonists such as Yohimbine or dopamine receptor agonists such as Apomorphine (Porst, 2002; Pryor, 2002; Fink et al., 2002; Drewes et al., 2003). The high cost of these conventional treatments as well as the poverty of the populations of African countries have aroused in recent years a growing interest and a strong demand for traditional herbal medicines. Several plants are then used by African populations as having aphrodisiac properties that is to say that they are known to be able to create or stimulate sexual desire (Tajuddin et al., 2004; Singh et al., 2013a). Some of these plants have been the subject of scientific research (Tajuddin et al., 2003; Watcho et al., 2006; El-Tantawy  et al., 2007; Sanda et al., 2012) and others not researched on. This is the case of Spathodea campanulata P. Beauv. (Bignoniaceae) locally called "foukfouk" or "foufougue" which is used by traditional healers in the region of West-Cameroon (Roger et al., 2015) and West African regions for the treatment of ED (KondakuMbuta and Institute for Health Sciences Research, Forest Genetic Resources Program in Sub-Saharan Africa, 2012). Thus, it is essential to make a scientific contribution to their use.

This study was undertaken to evaluate the  aphrodisiac properties of aqueous extracts of the trunk bark of S. campanulata (Bignoniaceae) in albino rats (Rattus norvegicus).

Treatments of experimental animals

Thirty vigorous males submitted successfully to the grip test were divided into 5 groups of 6 rats each and treated orally as follows: Lot A (negative control) received 5 mL/kg of distilled water daily for 8 days, Lot B (positive control) received 5 mg/kg of Sildenafil Citrate (Viagra®) daily for 8 days, Lots C, D and E received 200, 400 and 800 mg/kg aqueous extract of the trunk bark of S. campanulata, daily for 8 days. These substances were administered using an orogastric feeding tube.

Study protocol for male sexual behaviour

The study was conducted between 13:00 and 17:00 to avoid any potential interference with the increase in natural libido observed in the mornings. The observations were then made on the 1st, 4th and 8th day of treatments administration. Thus, each rat was placed in a cage for 1 h for acclimation, and then a receptive female was introduced into the cage. The pair of animals was observed closely for 30 min. During this time, the following copulation parameters were counted and latency times measured:

(1) The frequency of the mounts which corresponded to the number of mounts, with or without intromissions preceding an ejaculation;

(2) The number of erections;

(3) The frequency of intromissions which corresponded to the number of intromissions preceding an ejaculation;

(4) The frequency of ejaculations which is the number of ejaculations recorded during the observation time;

(5) The latency of the ride which is the time between the introduction of a female in the cage and the first mount;

(6) The intromission latency time which is the time between the introduction of the female and the first intromission;

(7) The latency time of ejaculation which is the time that separates the first intromission from the first ejaculation (Pfaus et al., 2016).

Statistical analysis

Data were entered into an Excel spreadsheet (Microsoft Office 2007, USA) and analyzed with Statview software version 5.0 (SAS Institute, Inc., USA). Quantitative data were presented as mean ± standard deviation (SD) in graphs and tables. One-way order of variance analysis was used to compare the averages  between  two and more than two groups, respectively. The Newman-Keuls post hoc test was used to make the multiple pair comparisons. The materiality threshold was set at p-value 0.05.

Phytochemical screening

The phytochemical screening of the aqueous extract of the trunk bark of S. campanulata revealed the presence of the secondary metabolites shown in Table 1.

The overall objective of this study was to  evaluate the aphrodisiac properties of the aqueous extract of the trunk barks of S. campanulata P. Beauv, a plant used in parts of sub-Saharan Africa and particularly in the West Region of Cameroon to treat erectile dysfunction. The findings of this study shows that high dose administration with aqueous extract of S. campanulata trunk bark stimulated the copulatory activity of treated rat lots, compared to the negative control group.  Specifically, oral administration of the aqueous extract of S. campanulata to sexually experienced rats significantly increased the number of erections (p<0.05), frequency of mounts, intromissions and ejaculations for the lot received 400 mg/kg of aqueous extract of S. campanulata trunk bark. Latency mount and intromission time were reduced for the same batch, while ejaculation latency time significantly increased (p<0.05). Similar effects have been reported by Abedi et al. (2012) who evaluated the effects of the aqueous extract of pollen grains of Phoenix dactylifera on the sexual behavior of male rats. Thus, the extract would contain molecules that maintain erection and increase sexual motivation (Singh et al., 2013a).  This is confirmed by the significant increase in the frequency of erections and ascents as well as the decrease in the latency of rats in the extract-treated rats compared  to  the negative control rats. On the other hand, the decrease in the latency period of ascending and intromission is an indicator of an aphrodisiac action (Yakubu et al., 2007).  Indeed, the latency of riding and intromission are inversely proportional to the sexual motivation. Therefore, the significant decrease in elevation and intromission latency observed in rats receiving S. campanulata extract at 400 mg/kg on day 4 may suggest a stimulation of motivation and sexual arousal.  These results go in the same direction as those obtained by Sanda et al. (2012) who also observed a marked increase in the frequency of erections, ascites and a decrease in the latency of mount in normal adult rats treated with aqueous extracts of Allanblackia floribunda and Glycyrrhiza glabra.

From these results, we can suggest an increase in motivation and sexual desire induced by the aqueous extract of S. campanulata trunk bark. This pro-sexual effect could be attributed to the existence of saponins (Drewes et al., 2003), flavonoids and alkaloids revealed in phytochemical studies of this plant. Indeed, the steroidal nature of saponins could act as an intermediary in the androgen production pathway. Saponins could also bind to steroid hormone receptors, which could   lead    to  conformational  changes   and contribute to an increase in the function of these hormones; or they could bind to the enzymes involved in testosterone synthesis and increase its production (Gauthaman and Ganesan, 2008). Saponins also have a peripheral action by stimulating the release of nitric oxide (NO) in vascular smooth muscle (Abedi et al., 2012). The NO being a mediator involved in the relaxation of vascular smooth muscle tissue, will induce in erectile bodies of the penis, this increased vaso-relaxation is at the origin of an increase in the number of erections, hence the result that we got.

In addition, the reported antioxidant properties of S. campanulata (Mangambu et al., 2014) and well-known flavonoids (reported as an elevator of androgen levels in animals) (Pelissero et al., 1996) also contribute to the observed aphrodisiac effect.  Similarly, the presence of alkaloids, known for their ergogenic properties, can act either by inducing vasodilatation of the blood vessels through NO production and ultimately leading to erection or by stimulating steroidogenesis in animal testes.  Therefore, it is possible that the active ingredient contained in S. campanulata extract may have crossed the animal's blood-brain barrier to exert its aphrodisiac effect on the hypothalamic-hypophyso-testicular axis.  It is well documented that in erectile function, androgens stimulate the expression of the neuronal isoform of nitric oxide synthase (nNOS) and modulate the activity of phosphodiesterase type 5 (Mills et al., 1994).  Alkaloids can also act by relaxing the smooth muscles of cavernous bodies in the copulatory organ of male rats. This aphrodisiac effect would be completely different from the action of Viagra® (sildenafil citrate), the reference molecule used in this study. Indeed, sildenafil citrate is a non-androgenic aphrodisiac that acts directly on penile erectile tissue inhibiting the activity of phosphodiesterase type 5, the enzyme involved in the specific degradation of cGMP, the second messenger involved in the mechanism of erection. The prolonged action of cGMP is at the base of the aphrodisiac effect of sildenafil citrate.

This study focused on the evaluation of the aphrodisiac activity of the aqueous extract of S. campanulata P. Beauv. We obtained the different extracts and characterized the large groups of secondary metabolites present in the extract. In addition, we tested the aphrodisiac activity compared to distilled water as a negative control on one hand and sildenafil citrate (Viagra®) on the other hand, which is a reference aphrodisiac sold in pharmacies as a positive control. The qualitative analysis of extracts of S. campanulata P. Beauv shows the presence of flavonoids, alkaloids, phenolic compounds, tannins, reducing compounds, saponins and coumarins. The study of the aphrodisiac activity shows that S. campanulata P. Beauv increases sexual   desire   in   rats   significantly   compared   to  the negative control. Oral administration of the aqueous extract of the trunk barks of S. campanulata P. Beauv at doses of 200, 400 and 800 mg/kg body weight over a period of 8 days influenced the copulatory activity of normal and sexually experienced male Wistar albino rats. Compared with the animals in the negative control groups, the effects of the extract on the sexual behavior of the treated rats were materialized by stimulation of sexual motivation, effect confirmed by the increase in the frequencies of erections and mounts as well as the decrease in the latency of mount; stimulation of sexual performance, effect confirmed by the increase in the frequency of intromissions as well as the decrease of the latency of intromission; stimulation of sexual pleasure by an increase in the frequency of ejaculation and the latency of ejaculation, effect confirmed by the increase of the frequency of ejaculations and the increase of the latency of ejaculation (Singh et al., 2013b). It can be concluded that the aqueous extract of the trunk barks of S. campanulata P. Beauv have a pro-ejaculatory aphrodisiac effect. These results would justify the empirical use of this plant to fight against erectile dysfunction.

The authors have not declared any conflict of interests.