Effect of Watermelon (Citrullus lanatus) Flesh Extract on Sexual Behavior of Male Rats

Abstract

The effects of red watermelon (Citrullus lanatus) flesh extract on male sexual behavior as well as its adverse effects were investigated using animal models. The suspension of the flesh extract was administered orally at doses of 100, 500 and 1000 mg/kg to different groups of male rats (n = 5) daily for 22 days. The receptive female rats were prepared by hormonal treatment. The mat-ing behavior was investigated and compared with the standard reference drug, sildenafil citrate. The adverse effects of the plant extract were also evaluated by observing at least once daily for any sign of toxicity, water and food intake, stress and changes in behavior. The animal procedures were conducted in accordance with the Institutional Animal Care and Use Committee, Ubon Ratchathani Ra-jabhat University, Thailand. The results indicated that oral administration of watermelon flesh extract caused a significant increase in Mounting Frequency, Intromission Frequency and Ejaculatory Latency in first and second series and caused a significant decrease in the Mounting Latency and Intromission Latency (P<0.05). The extract at a dose of 1000 mg/kg did not produce clinical signs of toxicity or mortality in any of animals during the treatment duration. The weight of body and reproductive organs showed no significant difference in the flesh extract groups compared to the control group (P>0.05). Based on the aphrodisiac property of watermelon in animal models observed in this present study, this plant may be useful for men with erectile dysfunction. In addition, watermelon flesh extract did not produce undesirable effects on male rats, indi-cating that its short-term use is apparently safe. Thus, our findings support the use of watermelon flesh for increasing potency in males.

Full text

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CMUJ NS Special Issue on Food and Applied Bioscience (2014) Vol.13(1)
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Effect of Watermelon (Citrullus lanatus) Flesh Extract
on Sexual Behavior of Male Rats
Phukphon Munglue1*, Sajeera Kupittayanant2 and Pakanit Kupittayanant3
1Program of Biology, Faculty of Science, Ubon Ratchathani Rajabhat University,
Ubon Ratchathani 34000, Thailand
2School of Physiology, Institute of Science, Suranaree University of Technology,
Nakhon Ratchasima 30000, Thailand
3School of Animal Production Technology, Institute of Agricultural Technology,
Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand
*Corresponding author. E-mail: phukphon@ubru.ac.th
ABSTRACT
The effects of red watermelon (Citrullus lanatus) esh extract on male
sexual behavior as well as its adverse effects were investigated using animal
models. The suspension of the esh extract was administered orally at doses of
100, 500 and 1000 mg/kg to different groups of male rats (n = 5) daily for 22
days. The receptive female rats were prepared by hormonal treatment. The mat-
ing behavior was investigated and compared with the standard reference drug,
sildenal citrate. The adverse effects of the plant extract were also evaluated by
observing at least once daily for any sign of toxicity, water and food intake, stress
and changes in behavior. The animal procedures were conducted in accordance
with the Institutional Animal Care and Use Committee, Ubon Ratchathani Ra-
jabhat University, Thailand. The results indicated that oral administration of
watermelon esh extract caused a signicant increase in Mounting Frequency,
Intromission Frequency and Ejaculatory Latency in rst and second series
and caused a signicant decrease in the Mounting Latency and Intromission
Latency (P<0.05). The extract at a dose of 1000 mg/kg did not produce clinical
signs of toxicity or mortality in any of animals during the treatment duration.
The weight of body and reproductive organs showed no signicant difference in
the esh extract groups compared to the control group (P>0.05). Based on the
aphrodisiac property of watermelon in animal models observed in this present
study, this plant may be useful for men with erectile dysfunction. In addition,
watermelon esh extract did not produce undesirable effects on male rats, indi-
cating that its short-term use is apparently safe. Thus, our ndings support the
use of watermelon esh for increasing potency in males.
Keywords: Citrullus lanatus, Watermelon, Sexual behavior, Aphrodisiac, Male
rats
Doi: 10.12982/cmujns.2014.0054

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INTRODUCTION
Erectile dysfunction (ED) is a common disorder in older men, causing a
decrease in quality of life. Multiple risk factors are associated with ED, including
hypertension, diabetes, coronary artery disease, smoking and alcohol consumption
(Lue, 2000). In Thailand, the prevalence of ED has increased from 37.5% in 2000
to 42.8% in 2008 (Permpongkosol et al., 2008). Sildenal citrate or Viagra has
been used to increase potency, sustain satisfactory erections and improve sexual
satisfaction without affecting sexual desire in men with ED (Lue, 2000; Park et al.,
2011). However, sildenal citrate may do harm to patients with coronary ischemia
or congestive heart failure, or patients taking multidrug antihypertensive regimens
(Lue, 2000).
Several medicinal plants have long been used as aphrodisiacs to improve
sexual health in man worldwide, because they are apparently safe and have fewer
side effects (Sandroni, 2001; Drewes et al., 2003). Aphrodisiacs are substances that
can increase sexual function and sexual desire (Sandroni, 2001; Soni et al., 2012).
Sexual desire is modulated by the central nervous system (Soni et al., 2012). On
the other hand, sexual function is not always dependent on sexual desire, but
dependent on a neurovascular regulation via the hemodynamic mechanisms of
penile erection (Soni et al., 2012). It is generally accepted that medicinal plants are
composed of numerous chemical constituents, which usually exert their therapeutic
effects through multiple mechanisms (Drewes et al., 2003; Cao et al., 2008). The
nature of these actions results in either the stimulation (aphrodisiac) or inhibition
(anti-fertility) of sexual behavior. Watermelon, claimed to have aphrodisiac poten-
tial (Drewes et al., 2003; Figueroa et al., 2011; Jayaprakasha et al., 2011; Munglue
et al., 2012), has been receiving attention.
Watermelon (Citrullus lanatus) belongs to the family Cucurbitaceae and
is rich in the amino acids arginine and citrulline, which play important roles in
the production of the potent vasodilator, nitric oxide (NO) (Cormio et al., 2011;
Munglue et al., 2012; Rimando and Perkins-Veazie, 2005). NO is a physiological
signal acting to regulate the mechanisms underlying penile erection through the
activation of soluble guanylate cyclase to convert guanosine triphosphate to cyclic
guanosine monophosphate (cGMP) (Sandroni, 2001; Drewes et al., 2003; Cormio
et al., 2011; Estrada-Reyes et al., 2013;). In addition, oral L-citrulline supplemen-
tation can improve penile erection in men with mild ED (Cormio et al., 2011).
Ethnopharmacological relevance demonstrated that watermelon supplementation
can improve aortic hemodynamics in patients with prehypertension, suggesting
that watermelon has a potent vasodilator (Collins et al., 2007; Figueroa et al.,
2011). In addition, watermelon extract induces the relaxation of smooth mus-
cle cells through NO pathway modulation and reduction of intracellular Ca2+
[Ca2+]i (Jayaprakasha et al., 2011). Recently, our data indicated that watermelon
extracts can exert their effects in rat isolated uterine strips by inhibiting Ca2+ inux
and some of the Ca2+ signaling element involved in smooth muscle contraction
(Munglue, 2011; Munglue et al., 2012). Watermelon has been reported to have
tocolytic properties (Jayaprakasha et al., 2011; Munglue et al., 2012). Few studies
have examined the effects of watermelon extract on female reproductive phy-

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siology (Jayaprakasha et al., 2011; Munglue et al., 2012); its effect on male sexual
behavior has not yet been elucidated.
To the best of our knowledge, the effect of watermelon esh extract on male
rat sexual behavior has not been examined and the safe use of this plant should be
evaluated. As there is an urgent need to nd better drugs with fewer undesirable
side effects to improve sexual performance, and novel compounds are sought
(Drewes et al., 2003), the aims of the present study were, therefore, to investigate
the effects of watermelon esh extract on sexual behavior along with its adverse
effects on sexually active male rats.
MATERIALS AND METHODS
Plant material collection
The fruits of watermelon were collected locally in the Province of Ubon
Ratchathani, Thailand, where the plant was cultivated under natural conditions.
Voucher specimen was identied and deposited at the Program of Biology, Faculty
of Science, Ubon Ratchathani Rajabhat University, Thailand.
Plant extraction
The watermelon fruit was cleaned, the esh isolated from the rind and the
seeds removed. Watermelon esh was dried in a hot air oven at 60°C for 4 days
(Munglue, 2011). Dried watermelon esh was extracted with ethanol (70%) and
evaporated under vacuum to yield 45% (weight/weight [w/w] based on the dried
starting weight). Watermelon esh extract was suspended in distilled water and
administered orally by intragastric tube.
Animal preparation
The experiments conducted were in accordance with the guidelines of the
Committee on Care and Use of Laboratory Animal Resources, National Research
Council, Thailand. The animal procedures were conducted in accordance with
the Institutional Animal Care and Use Committee, Ubon Ratchathani Rajabhat
University, Thailand. Twenty-ve 25 male (weighing 350-400 g) and 10 female
(weighing 200-250 g) Wistar rats were used in this study. They were housed
under standard conditions, and were fed on standard diet with water ad libitum
(Wethangkaboworn and Munglue, 2013).
The male rats were randomly divided into ve groups of ve animals each:
Group I: received distilled water orally and served as control.
Group II: received the watermelon esh extract 100 mg/kg body weight
daily (WF 100).
Group III: received the watermelon esh extract 500 mg/kg body weight
daily (WF 500).
Group IV: received the watermelon esh extract 1000 mg/kg body weight
daily (WF 1000).
Group V: received sildenal citrate 5 mg/kg body weight, one hour prior
to the experiment and served as a standard group.

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The female rats used for mating test were made receptive by hormonal treat-
ment (Sandroni, 2001; Wethangkaboworn and Munglue, 2013). Briey, female
rats were given an oral dose of ethinyl estradiol suspension (100 µg/animal) 48 h
prior to the experiment. Then, the animals were injected with progesterone subcu-
taneously at a dose of 1 mg/animal 6 h before the sexual behavior test (Sandroni,
2001; Wethangkaboworn and Munglue, 2013).
Effect on sexual behavior
Sexual behavioral examination was observed at 22 days of drug treatment.
Single male rats were gently dropped in 60×50×40 cm glass cages and acclima-
tized for 5 min. Then, a receptive female was presented to the male by placing
it gently into the cage. The sexual parameters were recorded and calculated as
follows (Sandroni, 2001; Tajuddin et al., 2005; Wethangkaboworn and Munglue,
2013):
(a) time from the introduction of the female into the male’s cage to the rst
mount or Mounting Latency (ML).
(b) time from the introduction of the female to the rst intromission by the
male or Intromission Latency (IL).
(c) time from the rst intromission of a series to the ejaculation or Ejacu-
latory Latency (EL).
(d) time from the rst ejaculation to the next intromission by the male or
Post Ejaculatory Interval (PEI).
(e) number of mounts before ejaculation or Mounting Frequency (MF).
(f) number of intromission before ejaculation or Intromission Frequency
(IF).
Effect on body weight and reproductive organ weights
To examine the effect of the plant extract on the body weight of the animals,
treated rats were weighted on day 22 and compared to the control group. Then,
the animals were sacriced by asphyxiation with CO2. Testes, seminal vesicles,
prostate gland and epididymides were carefully removed, cleared from the adipose
tissue and weighted.
Adverse effects of the extract
All treated animals were observed daily for signs of toxicity and stress and
behavior changes. The parameters recorded were salivation, rhinorrhea, lachryma-
tion, ptosis, writhing, convolutions and tremors. Food and water intake was also
noted (Tajuddin et al., 2005; Wethangkaboworn and Munglue, 2013).
Statistical analysis
Data are expressed as mean ± standard error of the mean. Signicance
difference was analyzed using one-way analysis of variance (ANOVA). P value
<0.05 was considered statistically signicant (Wethangkaboworn and Munglue,
2013).

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RESULTS
Effect on sexual behavior
The results obtained with the test for general mating behavior showed that
oral administration of watermelon esh extract signicantly increased MF, IF, EL1
and EL2 (P<0.05) and caused a signicant decrease in ML and IL (P<0.05). The
standard reference drug, sildenal citrate, signicantly increased MF, IF, EL1,
EL2 and PEI and decreased ML and IL, when compared with the control animals
(P<0.05) (Table 1).
Table 1. Effect of watermelon extract on mating behavior in male rats observed
at 22 days of the treatment.
Parameters
Treatments
Control WF
(100 mg/kg)
WF
(500 mg/kg)
WF
(1000 mg/kg)
Sildenal
citrate
(5 mg/kg)
MF
10.18±1.47 13.25±4.68ns 15.00±3.87*16.50±2.12*27.50±2.84*
IF
7.50±0.28 11.25±0.75*12.15±1.50*14.25±1.45*16.75±1.31*
ML (in sec)
45.25±1.35 39.75±7.15ns 29.25±3.26*26.75±1.45*23.00±1.08*
IL (in sec)
57.50±3.37 55.79±6.57ns 45.04±2.07*39.08±1.09*27.50±0.67*
EL1 (in sec)
216.75±4.02 220.30±11.20ns 235.24±2.35*240.63±6.15*313.22±4.56*
EL2 (in sec)
281.25±8.91 286.24±4.36ns 298.75±1.64*301.75±1.87*385.25±4.49*
PEI (in sec)
370.19±2.32 366.23±2.90ns 355.24±5.14ns 350.12±2.10ns 180.12±1.49*
Note: WF = watermelon esh extract, MF = mounting frequency, IF = intromission frequency, ML = mounting
latency, IL = intromission latency, EL1 = ejaculatory latency in rst series, EL2 = ejaculatory latency in second
series, PEI = post ejaculatory interval. Values are expressed as mean ± SEM, n = 5 (number of animals in each
group). One-way analysis of variance (ANOVA) was used. *P value <0.05 was considered statistically signicant
when compared to the control group. ns = not signicant.
Effect on body weight and relative reproductive organ weights
The animals receiving the plant extract did not show any changes in body
weight or relative reproductive organ weights (Table 2) when compared to the
control animal group (P> 0.05).

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Table 2. Effects of watermelon extract on body weight and relative reproductive
organ weights of male rats observed at 22 days of the treatment.
Parameters
Treatments
Control WF
(100 mg/kg)
WF
(500 mg/kg)
WF
(1000 mg/
kg)
Sildenal
citrate
(5 mg/kg)
Body weight (g)
436.01±9.25 442.09±8.71ns 432.02±8.65ns 440.74±7.29ns 435.08±8.95ns
Prostate gland
(g%)
0.24±0.02 0.23±0.01ns 0.24±0.01ns 0.24±0.01ns 0.24±0.01ns
Seminal vesicles
(g%)
0.33±0.03 0.36±0.02ns 0.33±0.04ns 0.35±0.03ns 0.35±0.02ns
Testes (g%)
0.91±0.02 0.93±0.04ns 0.84±0.02ns 0.96±0.04ns 0.83±0.02ns
Epididymides
(g%)
0.26±0.01 0.26±0.01ns 0.23±0.01ns 0.27±0.01ns 0.26±0.01ns
Note: WF = watermelon esh extract, Values are expressed as mean ± SEM, n = 5 (number of
animals in each group). One-way analysis of variance (ANOVA) was used. *P value <0.05 was
considered statistically signicant compared to the control group. ns = not signicant.
Adverse effects of the extract
The plant extract did not produce any sings of toxicity, stress or changes in
behavior. The food and water intake was similar to the control animals. In addition,
the extract at a high dose, 1000 mg/kg, did not cause treatment-related signs of
toxicity or mortality in any of the animals during the treatment period.
DISCUSSION
The results indicated that the watermelon plant extract caused a signicant
increase in potency or sustained erection. In addition, it was also observed to be
devoid of any sign of toxicity.
ML and IL are parameters of sexual arousal (Tajuddin et al., 2005; Suresh et
al., 2009). Furthermore, MF and IF are indicators of libido and potency (Tajuddin
et al., 2005; Suresh et al., 2009). The decreases in ML and IL and the increases in
MF and IF produced by watermelon esh extract revealed that this plant may be
a useful sexual stimulant.
EL and PEI are important for evaluating prolonged duration of coitus and
the rate of recovery from exhaustion after the rst series of mating, respectively
(Tajuddin et al., 2005; Suresh et al., 2009). Medicinal plants with an aphrodisiac
property should increase EL and decrease PEI (Tajuddin et al., 2005; Suresh et
al., 2009). In this present study, watermelon extract increased EL and tended to
decrease PEI. Thus, our results support this suggestion.
Sildenal citrate was able to produce very signicant decreases in ML, IL and
EL and increases in MF and IF, when compared to the plant extract. However, in
this experiment, the standard reference drug, sildenal citrate, was used to evaluate
the quantitative value and not to compare the mechanisms of action (Tajuddin et
al., 2005).

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It has been reported that substances that affect potency are generally
mediated through induction of vasodilators, NO and cGMP (Sandroni, 2001; Es-
trada-Reyes et al., 2013). Our nding on the stimulatory effect of watermelon esh
extract on male rat sexual behavior might be due to NO-cGMP relaxant pathway
modulation (Drewes et al., 2003; Jayaprakasha et al., 2011; Munglue et al., 2012;
Estrada-Reyes et al., 2013;). It was demonstrated that ethanolic extracts of wa-
termelon esh and rind produced a signicant decrease in rat uterine contraction
through the activation of NO production (Munglue et al., 2012). In addition, the
inhibitory effects of the plant extracts on uterine smooth muscle can be a result of
the addition of NO inhibitors (Munglue et al., 2012). These results indicated that
watermelon is a potent tocolytic.
The major constituents found in watermelon are citrulline, arginine,
lycopene and ß-carotene (Rimando and Perkins-Veazie, 2005; Jayaprakasha et al.,
2011). Previous studies have indicated that both citrulline and arginine were able
to improve sexual function in patients with erectile dysfunction (Zorgniotti and
Lizza, 1994; Melman, 1997; Cormio et al., 2011;). Hence, the aphrodisiac property
of watermelon might be due to citrulline, arginine or such compounds found in this
plant. Further research is needed to identify the active compound(s) responsible
for its aphrodisiac activity and the mechanisms underlying its action.
In this present study, the plant extract did not cause any side effects or
deaths during the treatment period. In addition, treated animals experienced no
changes in general behavior, body weight and relative reproductive organ weight.
Food and water intake were similar to those of the control animals, which sug-
gested that watermelon could be used for a long time without producing signs of
toxicity or treatment-related adverse effects.
CONCLUSION
Based on the aphrodisiac property of watermelon in animal models ob-
served in this present study, this plant may be useful for the treatment of erectile
dysfunction. In addition, watermelon esh extract did not produce any undesirable
effects on male rats, indicating that its short-term use of this plant is apparently
safe. Thus, our ndings support the use of watermelon esh for increasing potency
in males.
ACKNOWLEDGEMENTS
We gratefully acknowledge the nancial support of Ubon Ratchathani
Rajabhat University, Thailand. We are also thankful to Suranaree University of
Technology, Thailand, for providing all the facilities to carry out the study.

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