INTRODUCTION
Telfairia occidentalis Hook F (Cucurbitaceae), popularly known
as fluted pumpkin is cultivated mainly in West Africa, especially Nigeria,
Ghana and Sierra Leone (Akoroda, 1990; Bosa et al., 1983). It is
grown for its leaf and its oily seeds. The leaves are cooked and eaten
while the seeds which contain about 30% protein can be boiled and eaten,
or ground into powder for soup. The seed can also be fermented for several
days and eaten as a slurry (Asiegbu, 1987; Odoemena, 1991; Lucas, 1988;
Badifu et al., 1991). The medicinal importance of the plant is
being gradually investigated. T. occidentalis is now known to
possess anti-inflammatory effect (Oluwole et al., 2003), anti-bacterial
activity (Odoemena et al., 1995), erythropoietic value (Ajayi et
al., 2000) anticholesterolemic and immune building properties (Eseyin
et al., 2005a) and hypoglycaemic effect (Eseyin et al.,
2000; Eseyin et al., 2005b; Aderibigbe et al., 1991; Nwozo
et al., 2004).
The seed of T. occidentalis is a rich source of minerals such
as calcium, phosphorous, iron, zinc and copper. The seed contains 47%
oil. The oil obtained from the seed contains 61% unsaturated fatty acids
which offer protective role against atherosclerosis and cardiovascular
disease (Odoemena et al., 1998).
The phospholipis, glycolipids and neutral lipid contents of the seed
are 58, 26 and 15%, respectively (Anosike, 1994).
Both the leaf and root (Unpublished data) of T. occidentalis have
been screened for hypoglycemic activity. This research was undertaken
to screen the seed of T. occidentalis for possible hypoglycemic
activity, since the leaf has been confirmed to possess this activity.
MATERIALS AND METHODS
Plant materials: Fresh and mature pods of T. occidentalis
were purchased at Ikot Edim village in Ika local government area of Akwa
Ibom State, Nigeria. The pods were sliced open and the seeds removed and
washed. The seed coats were removed and the endosperm was pulverized with
a homogeniser.
Extraction: The seed powder was soaked in 96% ethanol for 72 h.
The extract obtained was filtered and concentrated in vacuo with
a rotary evaporator. The brownish residue obtained was dried in a desiccator.
Animals: Wilstar albino rats obtained from the animal house of
the university of Uyo were used. Unless otherwise indicated the animals
had free access to standard pelleted rat feeds and tap water. They were
kept under the care of experienced animal technicians. Food was withdrawn
overnight before experiments. Approval for this research was obtained
from the Animal Ethics committee of the University of Uyo.
Induction of diabetes: Diabetes was induced in rats by intraperitoneal
injection of 150 mg kg-1 alloxan monohydrate. The rats were
allowed to rest for seven days to stabilize the blood glucose concentrations.
All rats with glucose level above 5.5 mmol L-1 were considered
diabetic and used.
Effect of extract on blood glucose level in normoglycemic rats:
Fifteen overnight faster normoglycemic rats were divided into three equal
groups A, B and C. Each group was given parenterally 1 mL distilled water,
250 mg kg-1 and 100 mg kg-1 of the seed extract.
Blood glucose level was determined at 0, 1, 2 and 4 h.
Effect of extract on oral glucose tolerance
When seed extract was administered simultaneously with Glucose: Fifteen
rats were divided into three equal groups-Groups A, B and C were given orally
glucose (1 g kg-1) only; glucose (1 g kg-1) and 250 mg
kg-1 seed extract; glucose (1 g kg-1) and 100 mg kg-1
seed extract, respectively. Both the glucose and extract were administered simultaneously.
Blood glucose concentration was determined at 0, 15, 30, 45 and 60 min.
When seed extract was administered 1 (one) hour before glucose: Fifteen
rats were divided into three equal groups A, B and C. Each group received
glucose (1 g kg-1) one hour after they were given distilled
water, 250 mg kg-1 seed extract and 100 mg kg-1
seed extract, respectively.
Blood glucose level was determined at 0, 15, 30, 45 and 60 min after
administration of glucose.
Effect of seed extract on blood glucose level in alloxan induced diabetic
rats: Fifteen alloxan diabetic rats were divided into 3 equal groups
A, B and C. Each group received 100 and 250 mg kg-1 of the
seed extract and distilled water only, respectively. Blood glucose level
was determined at 0, 1, 2 and 4 h.
Phytochemical screening: Standard methods were used to undertake
the phytochemical screening of the ethanolic seed extract of T. occidentalis.
Determination of blood glucose concentrations: Blood samples were
obtained from the tail vein of the rats and were analysed using One TouchR
glucometer (Lifescan Inc., USA).
Statistical analysis: Data were expressed as Mean±SEM,
n = 5. The data were analysed by ANOVA and scheffe’s post test: p<0.05
was taken as significant.
Percentage variation in blood glucose level was calculated by the formula:
| Gt |
= |
Blood glucose concentration at time t |
| Go |
= |
Blood glucose concentration at time 0 |
RESULTS AND DISCUSSION
The results show that the ethanolic seed extract of T. occidentalis
did not have any significant hypoglycemic effect on normoglycaemic rats
at the dose of 100 and 250 mg kg-1 (Table 1).
And when administered to glucose (1 g kg-1) loaded rats either
simultaneously or 1 h before glucose loading, the extract did not lower
the glucose level at any of the dose levels. Rather, a significant increase
in blood glucose concentration was observed at 45 min in rats which received
glucose one hour after the administration of extract (Fig.
1 and 2).
However, 100 mg kg-1 of the extract significantly reduced
blood glucose concentration at the dose of 100 mg kg-1 at 1,
2 and 4 h. 250 mg kg-1 of the extract did not show this effect
(Table 2).
Phytochemical screening of the extract indicated the presence of alkaloids,
steroids, tannins and terpenes.
| Table 1: |
Effect of the seed extract of T. occidentalis on
the blood glucose concentration (mmol L -1) of normoglycaemic
rats |
|
Mean±SEM, * p<0.05, n = 5, Figures in parenthesis
represent percentage change in blood glucose concentration |
| Table 2: |
|
|
Mean±SEM, * p<0.05, n = 5, Figures in parenthesis
represent percentage change in blood glucose concentration |
|
| Fig. 1: |
Effect of the seed extract of T. occidentails
on the blood glucose concentration (mmol L -1) when administered
simultaneously with glucose (1 g kg -1) |
The hypoglycaemic effect of the leaf of Telfairia occidentalis has
already been confirmed. Hypoglycaemic activity of the seed extract (100
mg kg-1) was observed only in the alloxan induced diabetic
rats and none in the normoglycaemic rats. In the normoglycaemic rats the
Beta cells of the pancreas which produce insulin are intact. But alloxan
destroys these Beta cells. Alloxan induced diabetic rats therefore no
longer have functional pancreatic Beta cells and have lost the capacity
to secrete insulin which is required for glucose absorption. It could
be inferred therefore that the hypoglycaemic effect of the seed extract
is not mediated through the stimulation of insulin release from Beta cells
like the sulphonylureas (Akhtar et al., 1981)but through other
mechanisms (Sharma et al., 1983).
Oral Glucose Tolerance Testing (OGTT) is a standard procedure used in
the diagnosis of diabetes and in assessing extracts for hypoglycaemic
effect (Meigs et al., 2003). The observed reduction of blood glucose
concentration in glucose loaded rats at 60 min (when administered simultaneously)
and an increase in blood glucose level at 45 min (when administered 1
h before glucose) shows that the seed extract is not effective in reducing
blood glucose concentration in glucose loaded rats. This further buttresses
the fact that the seed extract did not stimulate insulin production by
the pancreas.
|
| Fig. 2: |
Effect of the seed extract of T. occidentails
on the blood glucose concentration (mmol L -1) when administered
1 h before glucose (1 g kg -1) |
It is therefore clear that the seed extract may be useful in the management
or ethnotherapy of type 2 diabetics mellitus. The seed of T. occidentalis
is known to contain about 14.5% carbohydrates. (mostly sucrose, fructose,
galactose, raffinose and stachyose), 47% lipids (phospho lipids - 58%,
glyco lipids -26%, neutral lipids-16%) with the fatty acids exhibiting
a high degree of unsaturation contributed mainly by the C 16 and C 18
fatty acids (Odoemena et al., 1998). And this study has shown that
the seed contains alkaloids, steroids, tannins and terpenes. However,
it is difficult at this stage to know which of these constituents of the
seed of T. occidentalis is/are responsible for the hypoglycaemic
activity. It is also not known why 250 mg kg-1 of the seed
extract did not reduce blood glucose level in the diabetic rats like the
100 mg kg-1 dose. It may be that at that dose level (250 mg
kg-1) the carbohydrate content of the extract contributed significantly
to the blood glucose level. Thereby countering the hypoglycemic effect
of the extract. This work shows for the first time that the seed extract
of T. occidentalis contains hypoglycaemic constituents which could
be useful in the treatment of non-insulin dependent (i.e., type 2) diabetes
mellitus.
ACKNOWLEDGMENT
The authors wish to thank Dr. F.S. Oluwole of the Department of Physiology,
University of Ibadan and Dr. O.A. Aderibigbe of the University of Ilorin
for the useful literatures they sent on request.
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