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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 7  |  Issue : 2  |  Page : 47-55

Aphrodisiac Potentials of Pausinystalia yohimbe (K. Schum.) Pierre ex Beille Methanol Root Extract in Male Wistar Rats


1 Department of Biological Sciences, Phytomedicine Research Centre, Botany Unit, Ondo State University of Science and Technology, Okitipupa, Nigeria
2 Department of Plant Biology and Biotechnology, Phytomedicine Unit, University of Benin, Benin City, Nigeria

Date of Submission17-Jun-2020
Date of Decision04-Jan-2021
Date of Acceptance25-Jan-2021
Date of Web Publication25-Aug-2021

Correspondence Address:
Dr. Adekunle Orimisan Ojatula
Department of Biological Sciences, Phytomedicine Research Centre, Botany Unit, Ondo State University of Science and Technology, Okitipupa
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jina.jina_7_20

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  Abstract 


Background and Objectives: Pausinystalia yohimbe is an evergreen (tree) medicinal plant that is being used across the globe in ethnomedicine to enhance libido in male. Therefore, this study is to investigate the in vitro aphrodisiac potential and acute toxicological effect of P. yohimbe roots in male Wistar rats. Materials and Methods: Forty-five male albino rats were randomly divided into five groups of nine rats each. Rats in Group 1 (control) were administered 1 mL/kg body weight distilled water (vehicle), Group 2 received 5 mg/kg body weight sildenafil citrate (Viagra), while those in Groups 3, 4, and 5 were given 25, 50, and 100 mg/kg body weight, respectively, of methanol extract of P. yohimbe root in the same volume. Female albino rats were made receptive by hormonal treatment. Sexual behavior parameters in male rats were monitored on days 1, 7, and 14 by pairing with receptive females. Computed male sexual behavioral parameters, male serum testosterone concentrations, and acute toxicological assay of the plant were also determined. Results: Oral administration of P. yohimbe root extract at the doses evaluated, except the lowest dosed group on day 1, significantly increased mount, intromission, and ejaculation frequencies (P < 0.05). The latencies of mount and intromission were significantly decreased and ejaculation latency was prolonged. Administration of the extract also reduced the postejaculatory interval significantly. The standard drug (sildenafil citrate) was not effective than the extract. The extract significantly increased the computed male sexual behavioral parameters as well as serum testosterone concentrations, compared with the distilled water control. The toxicity studies showed that there were no acute behavioral changes with zero mortality. Conclusions: The result of this study demonstrates that methanol extract of P. yohimbe root enhances sexual behavior in male rats. The aphrodisiac effects of the plant extract may be related to the increased blood testosterone concentrations caused by the action of bioactive compounds present in the extract, acting via a multitude of central and peripheral mechanisms. Data from this study thus support the folk use of the plant material as an aphrodisiac in males.

Keywords: Aphrodisiac, complementary therapies, ethnomedicine, male sexual behavior, medicine, Pausinystalia yohimbe, traditional


How to cite this article:
Ojatula AO, Idu M, Timothy O. Aphrodisiac Potentials of Pausinystalia yohimbe (K. Schum.) Pierre ex Beille Methanol Root Extract in Male Wistar Rats. J Integr Nephrol Androl 2020;7:47-55

How to cite this URL:
Ojatula AO, Idu M, Timothy O. Aphrodisiac Potentials of Pausinystalia yohimbe (K. Schum.) Pierre ex Beille Methanol Root Extract in Male Wistar Rats. J Integr Nephrol Androl [serial online] 2020 [cited 2022 Aug 14];7:47-55. Available from: http://www.journal-ina.com/text.asp?2020/7/2/47/324509




  Introduction Top


Sexual relationships are among the most important social and biological relationship in human life, and sexual health is an important component of an individual's quality of life and well-being.[1] One of the main aims of marriage is procreation (reproduction) to ensure the continuity of an individual's lineage and more importantly for sexual fulfillment of both partners. For life to continue, an organism must reproduce itself before it dies.[2] All living organisms strive to achieve this through the process of reproduction, which is the vital process that enables a species to represent itself in the following generation in the form of its offspring.

In human, reproduction is initiated by the mating of a male with a female in sexual intercourse which facilitates the coming together of sperm and egg for the purpose of fertilization.[3] In order to have a normal sexual intercourse and sexual fulfillment in males, the male sexual organs and factors relating to erection must function normally. The recurrent or repeated inability of the male to perform a satisfactory sexual function or any disorder that interferes with his full sexual response cycle is termed male sexual dysfunction.[4] Male sexual dysfunction is an important contributor of male infertility with about 30%–50% of infertility cases attributed to problems with males alone.[5] Apart from other underlying causes, male sexual dysfunction is a pathology that occurs naturally as age advances,[6],[7] and it is reported as having a prevalent rate of 10% across all ages,[8] and because sexual dysfunction is an inevitable process of aging, the prevalence is over 50% in men between 50 and 70 years of age.[9] Male sexual dysfunction is a disorder of desire that leads to persistent absence of sexual fantasy and desire for sexual activity,[10] while erectile dysfunction, a subject of the main dysfunction, is the persistent inability to develop and maintain a penile erection that is suitable for penetration during sexual intercourse and ejaculation in 50% or more of attempts,[10] disorder of ejaculation, which involves problem with expulsion of semen at the climax of the sexual act, disorder of orgasm, that is, delay in or absence of orgasm after a normal sexual excitement phase during sexual activity,[11] failure to detumescence, that is, prolonged (>4 h duration) and extreme painful erection unaccompanied by sexual desire.[10] The causes of male sexual dysfunction include factors such as psychological disorders, hormonal condition, penile disease, neurological disorder, drug side effect, lifestyle, aging and systemic disease, and postorgan transplant.[12],[13]

Sexual inadequacy in human males has led to the development of a number of available treatment options leading to continuous search for potent natural agents that are needed to develop new, safe, and effective formulae for the treatment of male sexual dysfunction. Therefore, medicinal plants with marked pharmacological activities are readily available all year round, cheap and accessible and often with minimal side effect,[14],[15] and are being explored globally as alternative remedy.

One of the approaches for the management of male sexual dysfunction is by the use of aphrodisiac, either of plant or animal origin. The use of plants or their products to treat sexual disorders has a long history in most countries, and their investigations in animals have proven that they are effective in improving sexual desire and sexual behavior in male animals. Some of these include yohimbine, Microdesmis keayana, Massularia acuminata, Montanoa tomentosa,[16],[17] and so forth. Meanwhile, aphrodisiacs of plant origin have been implicated in treating/managing different arrays of sexual disorders.[18] Most aphrodisiacs can be said to amplify some facets of sensual experience such as light, touch, smell, taste, and hearing. This improved sensual consciousness that leads to sexual stimulation and inclination.[19] An aphrodisiac can, therefore, be described as any substance or agent (food, drug, scent, or device) that stimulates the erotic instinct, induces venereal desire and surges pleasure and performance, and as well, changes impaired sexual functions.[2],[13] Aphrodisiac substances can nevertheless be screened for activity by employing two methods: the observatory or physical method that encompasses the mating behavioral study and biochemical method. In either of the method, in vivo and in vitro animal models are used to ascertain aphrodisiac activity in laboratory animals such as rats, mice, and guinea pigs.[20]

Although, through history, a lot of feature has qualified diverse substances having aphrodisiac property, but by means of two probable approaches – cultural and scientific. Culturally, via the famous doctrine of signature, many plant and animal parts have been tented as having aphrodisiac effect. A good example is the accepted belief of hunters of those eras when they consume definite parts of their prey to get the characteristics of those organs. Scientifically, based on mechanism of action, aphrodisiacs can be classified into three categories (aphrodisiacs that offer a high level of nutritional value, those with specific physiological effect, and those that are psychologically active in nature). Following the phytochemical and nutritional constituents described by Patel et al.,[21] medicinal plants have been implicated for aphrodisiac activity by containing appreciable quality and quantity biomolecules involving in processes that promote penile erection, vasodilatation, increase in testicular and/or serum cholesterol, and engorging of the penis for sexual performance. Many of the effective herbal aphrodisiacs are accessible and have slight or no side effects.[14] Although there are conventional treatment options, they have limited efficacy, hostile side effects, and contraindications in some disease states.[22] The side effects of sildenafil citrate (Viagra) – a popular aphrodisiac drug – include rashes, blurred vision, hypotension, facial flushing, and nasal congestion among others.[23]

Pausinystalia yohimbe (K. Schum.) Pierre ex Beille belongs to the family Rubiaceae. It is an evergreen species growing in West and Central Africa in lowland forests. The tree grows about 30 m tall, with a straight boles/trunk that is rarely larger than 50–60 cm in diameter. The bark is gray to reddish brown, with longitudinal fissures, easy to peel, and bitter tasting. The inner bark is pinkish and fibrous. The sapwood is yellowish and the heartwood is ochre yellow; the wood is fine grained and relatively dense and moderately hard. The leaves grow in groups of three, with short (about 2 cm) petioles. The blades are oval shaped, 11–47 cm long, and 5–17 cm wide. It exhibits tap root system, and the root can be erect, bend, folded, and branching. The fruit (January to March) is spindle shaped, measuring up to 2 cm long with narrowly elongated winged seeds. Its geographical spread is from South-Western Nigeria to Gabon and Zaire. Yorubas call it “Idagbon,” Ibos call it “Likiba,” while Hausas call it “Burantashi.”[24] Yohimbine is the principal indole alkaloid in the root of the West-African tree, P. yohimbe. It is possible that the positive effect of yohimbine on penile erection is not only related to its central effect but also to a peripheral sympatholytic activity.[25] Roots of P. yohimbe have been considered as aphrodisiac by the people of Ilaje and Ikale areas of Ondo State, Nigeria, for a long time, and to the best of our knowledge, this is the first time in literature, reporting the aphrodisiac effect of P. yohimbe root, as compared to the frequently used plant material of P. yohimbe, the stem bark, in the open literature. The folk medicine of the indigenous people of Ilaje area of Ondo State, Nigeria, claimed the P. yohimbe root to be more efficacious and potent in enhancing reproductive/sexual behavior activity in males than the stem bark.[26] Hence, the use of P. yohimbe methanol root extract in this research work with a view to validate the acclaimed ethnomedicinal use of this sexual invigorator in folk medicine.


  Materials and Methods Top


Plant material

Fresh roots of P. yohimbe were obtained from Ugawan Village, near the boundary of Okomu National Park, Udo, Edo State, Nigeria, during April to May 2015. The plant sample was identified and confirmed at the Herbarium of the Department of Plant Biology and Biotechnology of the University of Benin, Benin City, Edo State, Nigeria, with the voucher number UPBHx1066.

Preparation of plant material

Fresh roots of P. yohimbe were collected, thoroughly washed, and air dried inside the laboratory until constant weight was obtained. They were pulverized using an electric blender (RN4S, Mayer, China) and sieved to obtain the powdered form. One thousand two hundred grams of the powdered form was extracted in 99% absolute methanol using Soxhlet apparatus. The extraction was carried out in cycles at a temperature of 50°C, and each cycle lasted for 48 h. Extract was evaporated to near dryness and as well concentrated on a water bath under reduced pressure and low temperature. The slurry from methanol extract was later weighed and reconstituted in distilled water to give the required doses used in the study.

Drugs, assay kits, and other reagents

Estradiol benzoate and progesterone were purchased from Sigma-Aldrich from China and USA. Sildenafil citrate (Viagra) was obtained from a community pharmacy outlet in Okitipupa, Ondo State. The testosterone assay kit was procured from Monobind Inc., USA, while every other chemical used was of analytical grade.

Experimental animals

Sexually matured, healthy, albino rats of Wistar strain (Rattus norvegicus), weighing about 230–300 g (male) and 150–180 g (female), were obtained from the animal holding unit of the Department of Pharmacology and Toxicology, University of Benin, and were used for the experiments. The animals were allowed to undergo acclimatization period of 7 days and were housed in a ventilated wooden cage. They were kept at room temperature 28°C–30°C under natural light and dark cycle with free access to pelleted feed and tap water. Good hygiene was maintained by constant cleaning and removal of feces from the cage on a daily basis.

Animal grouping and administration of extract

A total of 45 male rats 3 months old (weighing 230–300 g) were selected for study. They were randomly divided into five groups, and ear tags and color codes were given to identify each animal. The negative control and positive control groups received 1 mL/kg of distilled water and 5 mg/kg of sildenafil citrate (Viagra) orally for 14 days. The extract was prepared in Tween-80 (1%), suspended in 1 mL/kg distilled water, and administered orally to the animals with the help of intragastric catheter at desired dose. The three test groups were administered orally with the methanol root extract of P. yohimbe on a daily dosage of 25, 50, and 100 mg/kg body weight, respectively, for 14 days.

Two days (48 h) before the commencement of the experiment, female rats 2.5 months old (weighing 150–180 g) were selected and each of them was administered with estradiol benzoate (10 μg/kg). Four hours before the exposure to males, each female rat was also given subcutaneous injection of progesterone (0.5 mg/kg) to ensure that the female rats were in estrous, this being the time when they were most receptive to fertilization.[13] Half hour after the dose administration on day 1 (after a single dose), day 7 (after seven doses, once daily), and day 14 (after 14 doses, once daily), three male rats from each of the groups were individually placed in separate cages and were monitored on experimental periods of days 1, 7, and 14 for sexual/mating behavior.

Determination of the methanol extract of Pausinystalia yohimbe root on male rats' sexual/mating behavior

The male sexual behavior test was carried out by the methods of Dewsburry and Davis[27] and that of Agmo[28] modified by Amin et al.[29] and Sumanta et al.[13]

The receptivity of the females was confirmed before the test by exposing them to the male rats that were not used for the experiments. Forty-five most receptive females (observed when females firmly raised their hind-limb quarters and tails to accept male sexual advances) were selected for the study. The experiment was carried out 2–3 h for diurnal doses on day 1, 7, and 14 on every onset of the dark in a quiet room (under red light), as this is the time when the Wistar rats are most active.[2]

Two independent observers blind to the conditions (test vs. control) manually scored by monitoring the behavior of the male rats. The male rats in separate cages were allowed 10 min adaptation period with the receptive females (1 female to 1 male). The occurrence of events and phases of mating after the video recording were analyzed and the frequencies and phases were determined. The parameters of male sexual behavior that were monitored for 15 min observation period after pairing include:

  • Mount frequency (MF): The number of times the males assumed copulatory position but failed to achieve intromission – characterized by lifting of the male's fore body over the hindquarter of the female and clasping her flanks with his forepaw
  • Intromission frequency (IF): The number of vaginal penetration made by the male
  • Ejaculation frequency (EF): The number of times there was expulsion of semen by the males after vaginal penetration – characterized by rhythmic contraction of the posterior abdomen. The female rats were also observed for the presence of vaginal plug. In addition, other standard parameters of sexual behavior obtained through manual data acquisition using stopwatch included
  • Mount latency (ML): The time from the introduction of the female until the first mount made by the male
  • Intromission latency (IL): The time from the introduction of the female until the first intromission by the male that is usually characterized by pelvic thrusting and springing dismount
  • Ejaculation latency (EL): The time from the first intromission until ejaculation usually characterized by longer, deeper pelvic thrusting and slow dismounting, followed by a period of reduced activity
  • Postejaculatory interval (PEI):The time interval from ejaculation to intromission of the next series. Some additional male sexual behavior parameters computed following Sumanta et al.[13] include:














intercopulatory efficiency = Average time between intromissioons

Preparation of serum

The male rats were anesthetized in a jar containing cotton wool soaked in chloroform. When the rats became unconscious, they were quickly brought out of the jar and the abdominal region was opened along the linea alba, cut with scalpel blade to expose the organs, and blood was collected into a sterile sample container by cardiac puncture. Later, the blood was transferred into a clean, dry centrifuge tube and allowed to clot for 30 min before centrifuging at 300 rpm × 10 min using Wifug Laboratory Centrifuge (model SM800B, a product of Eltex of Sweden Limited, Bradford, United Kingdom). The sera were thereafter aspirated into clean, dry sample bottles using Pasteur pipette and used for the determination of testosterone concentration within 12 h of preparation as described by Malomo.[30]

Determination of serum testosterone concentrations

The serum testosterone concentrations of the rats were determined on days 1, 7, and 14 of treatment using the procedure outlined in the manufacturer's instruction manual (Elecsys and Cobas enzyme immunoassay analyzers – products of Diagnostics Automation Incorporated, Calabasas, USA) which operates with the chemiluminescence immunoassay (CLIA) method.

The principle of the CLIA test follows the typical competitive binding scenario as described by Ooi[31] and modified by Murphy and Lee.[18] Competition occurs between an unlabeled antigen (present in standard, control, and samples) and an enzyme labeled antigen (conjugate) for a limited number of antibody binding sites on the microwall plates. The washing and decanting procedures remove unbound materials.

The washing step, the luminescence substrate solution is added. The relative luminescence units (RLUs) are measured on a microtiter plate luminometer. The RLU values are inversely proportional to the concentration of free testosterone in the sample. A set of calibrators were used to plot a standard curve from which the amount of free testosterone in samples and control can be directly read.[31]

Acute toxicity study

Twenty male rats were utilized in this study and extract earlier given as stated in the mating behavioral study. The animals were completely randomized into four groups of five rats each. In all the groups, the animals were monitored for 2 h for any behavioral change such as hyperactivity, sedation, salivation, diarrhea, accelerated breathing, tail posture, and convulsion after administering the extract (at the respective doses –25 mg/kg, 50 mg/kg, and 100 mg/kg), distilled water, and standard drug (Viagra) to the corresponding groups. The mortality or lethality was counted after 24 h, and the lethal dose (LD50) was determined. All animals were further observed for up to 14 days for any delayed mortality.

Statistical analysis

The results were expressed as mean ± standard error of mean of nine replicates. All the mean values were statistically analyzed using one way analysis of variance followed by Duncan's multiple range test and Chi-square test. The values were judged significant if P < 0.05. The Statistical Package for the Social Sciences (SPSS) computer software (version 20) a product of Eltex of Sweden Limited, Brandford, United Kingdom and Microsoft Excel (2013) software were used for data analysis.

Ethics approval/statement

The protocol for the study was approved on January 12, 2017, by the Ethical Committee (Ref. no: UNIBEN/NOEC/PBB_LSC/365/5) on Experimental Animal Use and Care of the Faculty of Life Sciences, University of Benin, Nigeria.


  Results Top


Effect of the methanol extract of Pausinystalia yohimbe root on sexual/mating behavior

The administration of the methanol extract of P. yohimbe root to male rats on day 1 at a dosage of 25, 50, and 100 mg/kg body weight did not manifest any noticeable effect on sexual behavior parameters investigated, whereas the standard drug-treated group of rats exhibited increased (P > 0.05) MF, IF, EF, and EL as well as decreased (P > 0.05) ML, IL, and PEI when compared to the negative control [Table 1].
Table 1: Effect of Pausinystalia yohimbe methanol root extract on male rats mating behaviors monitored on day 1

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However, following the administration of the plant extract on day 7, the male rats, upon introduction, responded with immediate advances toward the female and displayed precopulatory behavior such as chasing and anogenital sniffing which eventually culminated into mounting. The extract at a dosage of 25 and 50 mg/kg body weight was able to increase the MF, IF, EF, and EL and had a significant decrease (P < 0.05) in ML, IL, and PEI when compared to the negative control. In contrast, the highest extract-dosed group (100 mg/kg body weight) decreased (P > 0.05) the MF, IF, EF, and EL at day 7 and caused increased effect in the ML, IL, and PEI when compared with other dosed groups. The standard drug-treated group increased (P > 0.05) the MF, IF, EF, and EL, while ML, IL, and PEI decreased significantly (P < 0.05) compared to the negative control [Table 2].
Table 2: Effect of Pausinystalia yohimbe methanol root extract on male rats mating behaviors monitored on day 7

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At day 14, the various doses evaluated (25, 50, and 100 mg/kg body weight of the extract) showed increased (P < 0.05) effect on the MF, IF, EF, and EL parameters, while ML, IL, and PEI decreased (P < 0.05) significantly compared to the negative control. The standard drug-treated group produced contrasting effect on the parameters in which MF, IF, EF and EL decreased (P < 0.05), while ML, IL, and PEI increased (P < 0.05) when compared to the extract-dosed groups [Table 3].
Table 3: Effect of Pausinystalia yohimbe methanol root extract on male rats mating behaviors monitored on day 14

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The computed male rats' sexual behavior parameters which include percentage (%) index of libido, % mounted, % intromitted, % ejaculated, intromission ratio, and % copulatory efficiency were significantly (P < 0.05) higher in the extract-treated rats except the intercopulatory efficiency, which was reduced when compared to the control groups [Table 4].
Table 4: Effect of Pausinystalia yohimbe methanol root extract on computed male rat sexual behavior parameters

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Effect of the methanol extract of Pausinystalia yohimbe root on hormonal (testosterone hormone) levels

The methanol extract of P. yohimbe root at the dosage of 25, 50, and 100 mg/kg body weight produced increased (P > 0.05) levels of testosterone hormone at day 1, as well as increased (P < 0.05) significantly, the serum testosterone content of the male rats at the other days of intervention (i.e., days 7 and 14) compared to that of the treated positive and untreated negative controls males rats [Table 5]. Testosterone level was highest at 50 mg/kg body weight compared to that of the 25 and 100 mg/kg body weight following administration [Table 5].
Table 5: Effect of Pausinystalia yohimbe methanol root extract on serum testosterone concentration of male rats across days of treatment

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Acute toxicological study

Results from the acute toxicological studies revealed that the methanol extract of P. yohimbe was safe up to the highest dose of 100 mg/kg. No toxic symptoms or adverse behavioral changes were observed as zero mortality was recorded during the period of the study.


  Discussion Top


To the best of our knowledge, there is no scientific report on the aphrodisiac effects of the root extract of P. yohimbe in the open literature. The present study was, therefore, designed to scientifically investigate the folk use of P. yohimbe root as a sex stimulant. Overall, the root methanol extract of P. yohimbe enhanced the sexual activity of male rats in a day-dependent manner as revealed by the results of this study compared to the control rats [Table 1], [Table 2], [Table 3]. Its effects were not pronounced on day 1 [Table 1] of the study compared to days 7 and 14 [Table 2], [Table 3], as the effects exhibited were of better chances than those of sildenafil citrate (Viagra), the standard drug, at the doses of 50 and 100 mg/kg.

Phytochemical screening of the methanol root extract of P. yohimbe reveals the presence of alkaloids, flavonoids, saponins, steroids, tannins, and triterpenoids. Studies in laboratory animals such as rats have attributed the sexual stimulantion activity of medicinal plant to many components of plant extracts, as the possible bioactive agents causing increasing endogenous testosterone level and enhancing male sexual behavior. These include steroids and steroidal saponins, which may act as intermediaries in the steroidal pathway of androgen production. Saponins can bind to hormone receptors, resulting in conformational changes that can induce the physiological functions of the hormone, or can bind to hormone receptors involved in the synthetic pathway of the said hormones and, as a consequence, promote their production.[32] Furthermore, flavonoids have been involved in altering androgen levels and may also be responsible for enhancing male sexual behavior either by promoting testosterone synthesis that inhibits its metabolic degradation.[33]

The need for plants with sex-enhancing potential or aphrodisiacs with little or no side effect is of great concern. Various substances of animal and plant origin have been used in folk medicine of different cultures as aphrodisiac, some of which have been identified pharmacologically to exert their effects on the hypothalamic–pituitary–testicular axis.[34] Aphrodisiacs can be defined as substances which are ingested, applied topically, smoked/snorted, or otherwise delivered into the body to induce sexual arousal, heighten sexual experience, and to improve sexual performance.[34] Plant preparations including P. yohimbe as a sex enhancer have become prominent in folk medicine. To understand the scientific reasons behind these folk claims, hence the need for investigation of the effect of methanol extract of P. yohimbe root in this study. The parameters of the sexual behavior of the male albino Wistar rats such as MF, IF, EF, ML, IL, EL, PEI, and testosterone levels were used in this study.

Mount and intromission frequencies are useful indices of libido, sexual vigor, strength, power, and energy. The number of mount (MF) reflects sexual motivation; an increase in the number of intromission (IF) shows the efficiency of the erection, penile orientation, and the ease by which ejaculation reflexes are activated.[35] Therefore, the increase in MF and IF following administration on day 7 and day 14 of the observation days suggests enhanced libido. Such enhancement of libido might have arisen from increase in the concentration of several anterior pituitary hormones and serum testosterone which, in turn, stimulated dopamine receptor synthesis and sexual behavior.[36]

ML and IL are indices of sexual motivation, and there is an inverse relationship between ML, IL, and sexual motivation.[18] The extract was able to significantly decreased (P < 0.05) the ML and IL, and this might imply stimulation of sexual appetite and arousal, thus lending credence to the sexual improving effect of the extract under study just like other aphrodisiac plants that have been studied, e.g., M. tomentosa.[37]

Ejaculatory latency and ejaculatory frequency are pointers of enhanced copulatory performance. The extract was able to increase ejaculatory latency and ejaculatory frequency. Ejaculatory latency also implies prolonged coitus duration which translated into increased staying power, strength, and vigor, thus validating its aphrodisiac properties just like other aphrodisiac plants that have been investigated, e.g., Vanda tessellata.[38]

PEI is a positive marker of sexual potency, libido, and a fast pace of recovery from exhaustion after the first series of mating. The extract significantly decreased the PEI (P < 0.05) and compared favorably with other aphrodisiac plants that have been studied, e.g., Dactylorhiza hatagirea.[39]

Copulatory efficiency is an indication that the copulatory action of the male was well enhanced with well-coordinated pelvic thrusting, and this further indicates sustained increase in interest, focus, agility, and stamina in the sexual act. The extract at all dose levels was able to increase the copulatory efficiency significantly (P < 0.05), thus lending credence to its aphrodisiac potency which compares to other aphrodisiac plants that have been studied, e.g., Withania somnifera.[40]

The precopulatory and copulatory behaviors of the extract-treated rats showed that the rats were extremely aroused and the effects of the extract on the mating behavior were day dependent with the 50 mg/kg body weight been more potent. Sexual behavior and erection are largely dependent on androgen which may act through central and peripheral mechanism.[41] All doses of the extract increased testosterone supplementation which leads to improved sexual function and libido, in addition to the intensity of orgasm and ejaculation.

The observed improvement in mating behavior seen between the controls and the extract-treated groups may be due to plant chemicals present in the extract (alkaloids, saponins, phenols, flavonoids, tannins, steroids, and cardiac glycosides); these plant chemicals are able to exert their effect through elevation of androgens and gonadotropins, vasodilation, and generation of nitric oxide,[4] which are key factors in the initiation and sustenance of erection, libido, and other sexual factors.[3]

Toxicologically, all animals in all the groups showed no significant adverse acute toxicity effect that can be attributed to acute administration of the methanol extract of P. yohimbe. Furthermore, adverse changes in behavior were not observed, indicating that physical clinical signs were unremarkable. The intake of food and water was normal, suggesting that the animals had a normal appetite. No mortality was noticed during the entire period of the study. It can, therefore, be inferred that the LD50 of the extract is >100 mg/kg since up to this dose no death was recorded. This finding agrees with previous report by Morales et al.,[42] where 0% mortality was recorded when the aqueous leaf extract of Alchornea cordifolia at 3200 mg/kg was administered.


  Conclusions Top


As the results of this study suggest clear indication that the systemic use of the methanol extract of P. yohimbe root has marked enhancement on mating behavior parameters and the sex hormone of male rats, it may, therefore, be concluded that P. yohimbe root possesses aphrodisiac property, thus supporting the acclaimed aphrodisiac potential of the plant in folk medicine.

Acknowledgments

The authors are very grateful to Mr. Gabriel Benjamen of the Phytomedicine Unit, Department of Plant Biology and Biotechnology, University of Benin, for his technical assistance. The corresponding author is also grateful to his parents and siblings for their support.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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