Protective effect of Clerodendron glandulosum extract against experimentally induced metabolic syndrome in rats

Abstract

Context: Metabolic syndrome (MetS) has become one of the major health burdens worldwide. To date, no single pharmacological agent has been developed to correct metabolic abnormalities associated with MetS. Use of indigenous medicinal plants as alternative medicines against MetS could be beneficial due to multiple therapeutic usage, easy availability, and relatively few side effects.

Objective: To investigate the protective effect of Clerodendron glandulosum Coleb. (Verbenaceae) aqueous leaf extract (CgE) against experimentally induced MetS in rats.

Methods: Changes in body weight, food and fluid intake, plasma glucose, insulin, fasting insulin resistance index (FIRI), plasma total lipid profile, free fatty acids (FFA), oral glucose tolerance test (OGTT), blood pressure and vascular reactivity have been investigated in various experimental groups.

Results: Fructose+CgE groups recorded significant decrement (P <0.05) in plasma glucose, insulin, FIRI, total cholesterol, triglycerides, LDL, VLDL and FFA, whereas plasma HDL level was significantly increased (P <0.05) along with an efficient clearance of glucose during OGTT and lowered area under curve values. FRU+CgE groups also showed significantly decreased (P <0.05) mean arterial blood pressure along with decreased vasoconstriction and increased vasorelaxation in response to administration of various pharmacological agents. These results were comparable with metformin treated rats.

Discussion: C. glandulosum leaf extract ameliorates experimentally induced MetS by improving dyslipidemia and insulin resistance.

Conclusion: This study provides the first pharmacological evidence for the protective role of C. glandulosum leaves against experimentally induced MetS. Thus, therapeutic use of C. glandulosum in controlling MetS is indicated.

Keywords::

• Charles foster rats
• Clerodendron glandulosum aqueous extract
• dyslipidemia
• insulin resistance
• metabolic syndrome

Introduction

In 1988, Reaven introduced the concept that insulin resistance clusters with glucose intolerance, dyslipidemia and hypertension enhance cardiovascular disease (CVD) risk. Clusters of these metabolic disorders are now known as metabolic syndrome (MetS) (Grundy et al., 2004). Recently, MetS has become one of the major public health challenges worldwide. It has been estimate that 25% of the world’s population suffers from MetS (Dunstan et al., 2002). Such people have been categorized as the most vulnerable group likely to succumb to heart attack, stroke or death (Isomaa et al., 2001). In addition, people with MetS have a five-fold greater risk of developing type 2 diabetes (Stern et al., 2004) which adds to the tally of already existing 230 million diabetic patients worldwide (IDF, 2006). Until now, no known single pharmacological agent has been reported to correct the metabolic abnormalities associated with MetS. Hence, the endeavour of the scientific community is to tackle one or two metabolic disorders at a time to lower the overall magnanimity of MetS.

Currently, the research focus has been shifted towards the use of herbs and other alternative medicines in the treatment of diabetes, hypertension and dyslipidemia, as synthetic compounds have shown a number of side effects despite their proven bioactivities (Amos et al., 2003; Granberry et al., 2007; Thounaojam et al., 2009). The World Health Organization (WHO) has in fact recommended use of indigenous plants as an alternative remedy, especially in developing countries (WHO, 2002) where 80% of the population still relies on medicines of herbal origin as the main source of healthcare (Calixto, 2000). Medicines of herbal origin are perceived to be more effective, with minimal side effects, involve relatively low cost, and hence are prescribed widely by Ayurvedic practitioners even when their biologically active compounds are not known (Valiathian, 1998).

Clerodendron glandulosum Coleb. (Verbenaceae) kuthab laba is an herb endemic to northeastern states of India (Purkayastha et al., 2005). Traditionally, leaves of C. glandulosum are consumed by Apatani and Nyishi tribes of northeast India for treating hypertension (Kala, 2005; Deb et al., 2009), while tender shoots are used by the general populace of Dibru-Saikhowa Biosphere reserve of northeast India as a remedy for abdominal pain (Purkayastha et al., 2005). A recent study from our laboratory has reported the presence of flavonoids, polyphenols and ascorbic acid and the antioxidant property of C. glandulosum leaf extract (Jadeja et al., 2009a). A decoction prepared from dried powdered leaves of C. glandulosum is used traditionally in northeast India by a cross-section of people as a home remedy against hypertension, obesity and diabetes (Jadeja et al., 2009b). Urban people grow C. glandulosum in kitchen gardens and the leaves are commonly sold in urban areas of northeast India. Since diabetes, obesity and hypertension are integral parts of MetS (Grundy et al., 2004), we were inspired to initiate this study to assess the therapeutic potential of C. glandulosum leaf extract against experimentally induced MetS. Fructose-fed rats (FRU) that develop hypertension (Dai & McNeill, 1995), accompanied by the metabolic abnormalities of hyperinsulinemia, insulin resistance and hyperlipidemia (Basciano et al., 2005) are an ideal experimental model for preclinical evaluation of various therapeutic agents for the treatment of MetS (Yokozawa et al., 2007). Hence, the present study focuses on the protective role of C. glandulosum leaf extract against FRU-induced MetS in rats.

Materials and methods

Experimental animals

Male Charles Foster rats (180 to 200 g) were maintained in animal enclosures (24 ± 2°C) with a normal light:dark cycle (LD12:12). Rats were housed in clean polypropylene cages (six rats/group) and fed either control diet or high fructose diet and water ad libitum. The experimental protocol was carried out according to the guidelines of the Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA), India and approved by the animal ethical committee of the Department of Zoology, the M.S. University of Baroda, Vadodara (Approval No. 827/ac/04/CPCSEA).

Plant material

Fresh leaves of Clerodendron glandulosum were collected in the month of June from the natural habitat in Imphal District, Manipur, India and were authenticated by Hemchand Singh of the Department of Botany, D.M. College of Science, Imphal. A voucher specimen (No. 405) was deposited at the Department of Botany, D.M. College of Science, Imphal.

Preparation of extract

Leaves of C. glandulosum were washed with tap water, shade-dried and ground to obtain fine powder. Powdered leaves (100 g) were boiled in 1000 mL distilled water at 100°C for 3 h and filtered. Resulting filtrate was concentrated by heating to form a semi-solid paste which was then freeze dried. The yield was 28% w/w. Different doses of freeze-dried extract of C. glandulosum were prepared using 0.5% carboxy methyl cellulose (CMC).

Experimental design

Thirty rats were divided into five groups of six rats each as follows:

• Group 1. Control rats: Fed with control diet and received 0.5% CMC (p.o.) for 6 weeks

• Group 2. Fructose-fed rats (FRU): Fed with high fructose diet (60% fructose; Table 1) and received 0.5% CMC (p.o.) for 6 weeks

• Group 3. Fructose-fed + C. glandulosum treated rats (FRU+CgE 200): Fed with high fructose diet (60% fructose) and received 200 mg/kg body weight (BW) (p.o.) C. glandulosum extract for 6 weeks.

• Group 4. Fructose-fed + C. glandulosum treated rats (FRU+CgE400): Fed with high fructose diet (60% fructose) and received 400 mg/kg BW (p.o.) C. glandulosum extract for 6 weeks.

• Group 5. Fructose-fed + metformin treated rats (FRU+MET): Fed with high fructose diet (60% fructose) and received metformin (50 mg/kg BW) (Ansarullah et al., 2009) for 6 weeks.

Table 1.  Composition of diet.

Ingredients	Control diet (g%)	High fructose diet (g%)
Corn starch	60.0	−
Fructose	−	60.0
Casein	21.0	21.0
Methionine	0.7	0.7
Groundnut oil	5.0	5.0
Wheat bran	9.6	9.6
Salt mixture	3.5	3.5
Vitamin mixture	0.2	0.2

At the end of the experimental period (6 weeks), blood was collected from overnight (12 h) fasted animals via retro-orbital sinus puncture in EDTA coated vials. Plasma was obtained by cold centrifugation (4°C) of the vials at 3000 rpm for 10 min. Later the animals were sacrificed by decapitation under mild anesthesia and liver, pancreas, brain, and epididymal fat pad were excised and stored at −80°C for further analysis.

Biochemical analysis

Plasma glucose, total cholesterol (TC), triglyceride (TG), HDL-cholesterol (HDL), aspartate transaminase (AST) and alanine transaminase (ALT) were measured by enzymatic kits (Merck, Mumbai). The protocols for each enzymatic kit were executed as per the methodology provided by the manufacturer using semi-autoanalyzer (Micro Lab 300 L, Merck). Free fatty acid was estimated by the method of Itaya and Ui (1965). Briefly, a mixture of 6 mL chloroform, 0.1 mL plasma and 2 mL phosphate buffer (pH 6.2) were added to a glass-stoppered test tube and incubated at room temperature for 15 min. An aliquot of 3 mL of triethanolamine solution (1 M triethanolamine, 1 N acetic acid and 6.45% copper nitrate in the ratio of 9:1:10; v/v/v) was added to the test tube and the contents were mixed thoroughly and allowed to stand for 15 min. The aqueous and chloroform solutions formed two distinct layers in test tube. The upper aqueous layer was aspirated, whereas the residual chloroform layer was filtered. Diethyldithiocarbamate solution (0.1 mL) was added to the filtrate, the contents were agitated and optical density was read at 440 nm using UV-VIS spectrophotometer. Calculations were done using stearic acid as standard. Plasma insulin was assayed using a mouse insulin ELISA kit. The ELISA tests were performed as per the prescribed methodology of Mercodia Developing Diagnostics, Uppsala, Sweden, and the optical density was recorded on ELISA reader. Very low density lipoprotein-cholesterol (VLDL) and low density lipoprotein-cholesterol (LDL) were calculated by Friedewald’s formula: VLDL = TG ÷ 5 and LDL-C = TC-HDL + VLDL (Friedewald et al., 1972). Fasting insulin resistance index (FIRI) was calculated as: Fasting plasma glucose × Fasting plasma insulin ÷ 25 (Duncan et al., 1995).

Oral glucose tolerance test

A fresh set of rats were divided into similar experimental groups as above (n = 6) and used for the oral glucose tolerance test (OGTT), following the same treatment protocol consisting of five experimental groups. At the end of the experimental period (6 weeks) blood was collected from overnight fasted animals (0 h) by retro-orbital puncture method. Then glucose solution (30% in 0.9% NaCl) was orally administered (3 g/kg body weight) to all experiment groups and blood samples were subsequently obtained at 30, 60, 90, and 120 min in EDTA-coated tubes and plasma was separated. Plasma glucose concentration was determined by GOD-POD reagent method using standard kit (Merck, Mumbai).

Measurement of blood pressure and vascular reactivity

A fresh set of rats was divided into the above mentioned experimental groups (n = 6) and used for measurement of blood pressure and vascular reactivity in control and experimental groups (Balaraman et al., 2006). After completion of the treatment period, rats from each group were anesthetized using 1.2 g/kg (i.p.) of urethane. Tracheotomy was performed to facilitate breathing. The left common carotid artery and left femoral vein were cannulated with polyethylene tubing filled with heparinized saline (500 IU/ mL) to prevent clotting. The hemodynamic parameters like systolic, diastolic and mean arterial blood pressures (SBP, DBP, and MABP, respectively) were measured in the left common carotid artery using a pre-calibrated pressure transducer SS13L and Biopac MP-30 data acquisition system (BIOPAC Systems, Goleta, CA). After 30 min of equilibration vascular reactivity to intravenous (i.v.) injection (via femoral vein) of adrenaline (1 µg/kg), phenylephrine (1 µg/kg), isoprenaline (0.1 mmol/kg), and acetylcholine (0.1 mmol/kg) were recorded. Rats received a maintenance i.v. infusion of 0.9% sodium chloride (1 mL/h) throughout the experimental duration. All the data were analyzed using Biopac Student Lab Pro software (Version 3.6.7).

Histopathology of liver

Liver samples were fixed in 4% buffered paraformaldehyde, dehydrated in graded alcohol series and embedded in paraffin wax. Thick sections (5 μm) were cut, stained with hematoxyline and eosin, and examined under a Leica microscope and photographed with a Canon powershot S72 digital Camera (×100).

Statistical analysis

Statistical evaluation of the data was done by one way ANOVA followed by Bonferroni’s multiple comparison tests. The results are expressed as mean ± SEM using GraphPad Prism version 3.0 for Windows, GraphPad Software, San Diego, CA. The area under the curve (AUC_glucose) for OGTT was calculated based on trapezoid rule (GraphPad Prism version 3.0).

Results

Weight gain, food and fluid intake

FRU-fed rats recorded significant increment (p <0.05) in body weight gain (62.07%) without any significant alteration in food and fluid intake. There was a dose-dependent decrement (p <0.05) in body weight gain (27.7% and 49.09%), whereas there was a non-significant change in food and fluid intake in the FRU+CgE (200 and 400) groups (Table 2).

Table 2.  Effect of C. glandulosum Coleb. and metformin on weight gain, food intake, fluid intake, liver weight, aspartate transaminase (AST), alanine transaminase (ALT), glucose, insulin and FIRI.

	Control	FRU	FRU+CG200	FRU+CG400	FRU+MET
Weight gain (g)	12.36 ± 1.98	32.59 ± 2.03^###	23.56 ± 2.46^*	16.59 ± 2.7^**	25.99 ± 2.56^ns
Food intake (g/day)	10.24 ± 1.0	11.56 ± 1.21^NS	11.98 ± 1.09^ns	10.09 ± 1.56^ns	12.0 ± 1.34^ns
Fluid intake (mL/day)	34.37 ± 2.0	39.53 ± 1.98^NS	33.52 ± 2.31^ns	36.27 ± 2.12^ns	36.77 ± 2.08^ns
Liver weight (g)	4.56 ± 0.46	5.12 ± 0.4^NS	5.29 ± 0.39^ns	4.99 ± 0.41^ns	4.72 ± 0.5^ns
AST (U/L)	37.98 ± 2.09	45.36 ± 2.99^NS	40.25 ± 2.13^ns	44.09 ± 2.56^ns	39.09 ± 2.9^ns
ALT (U/L)	82.68 ± 4.9	86.26 ± 3.09^NS	79.76 ± 4.1^ns	80.09 ± 4.23^ns	84.57 ± 3.99^ns
Glucose (mg/dL)	100.6 ± 3.67	159.3 ± 5.19^###	137.6 ± 3.21^*	121.8 ± 7.46^***	121.1 ± 4.15^***
Insulin (pmol/L)	221.4 ± 12.42	465.1 ± 17.59^###	341.0 ± 9.056^***	306.8 ± 9.029^***	244.3 ± 16.4^***
FIRI	867.2 ± 51.82	2908 ± 213.1^###	1840 ± 69.63^**	1417 ± 73.45^***	1182 ± 132.4^***

^#p <0.05, ##p <0.01, ###p <0.001; NS, not significant when control versus FRU. *p <0.05, **p <0.01, ***p <0.001 and ns, not significant when FRU versus FRU+CG200, FRU+CG400 and FRU+MET.

Assessment of liver weight and function

Whole weight of liver of the control and experimental groups was similar, as the differences in weights were non-significant (Table 2). Also, the activity levels of plasma AST and ALT of experimental rats showed non-significant variations as compared to control rats.

Fasting blood glucose, plasma insulin and FIRI

FRU-fed rats demonstrated a significant increment (p <0.05) in fasting blood glucose (36.84%), plasma insulin (52.395%) and FIRI (70.17%), whereas FRU+CgE (200 and 400) groups showed lowered (p <0.05) blood glucose (13.62% and 23.54%), plasma insulin (26.68% and 34.03%) and FIRI (36.72% and 51%). FRU+MET group also showed significant decrement (p <0.05) in blood glucose (23.97%), plasma insulin (47.47%) and FIRI (59.32%) (Table 2).

Plasma lipid profile

FRU-fed rats demonstrated significant increment (p <0.05) in plasma TC (35.51%), TG (57.71%), LDL (65.23%), VLDL (57.71%) and FFA (51.82%) along with a significant decrement in HDL levels (47.05%) compared to control rats. FRU+CgE (200 and 400) groups showed significant decrement (p <0.05) in plasma TC (23.93% and 34.1%), TG (42.28% and 52.45%), LDL (43.56% and 60.22%), VLDL (42.28% and 52.46%) and FFA (27.02% and 42.69%) and a significant increment in HDL level (33.1% and 43.01%).These results were in accordance with results obtained in FRU+MET group (Table 3).

Table 3.  Effect of C. glandulosum Coleb. and metformin on plasma lipid profile.

	Control	FRU	FRU+CG200	FRU+CG400	FRU+MET
Cholesterol (mg/dL)	39.5 ± 1.43	61.25 ± 4.09^##	46.59 ± 2.87^*	40.36 ± 2.25^**	36.01 ± 3.49^***
Triglycerides (mg/dL)	51.93 ± 9.49	122.8 ± 8.93^###	70.87 ± 7.16^**	58.38 ± 7.56^***	67.62 ± 4.14^**
Free fatty acids (mg/dL)	32.19 ± 2.05	66.82 ± 4.38^###	48.76 ± 4.53^*	38.29 ± 3.16^***	44.52 ± 4.24^**
HDL (mg/dL)	24.27 ± 1.38	12.85 ± 0.95^###	19.21 ± 1.35^*	22.55 ± 1.72^**	20.83 ± 1.05^**
LDL (mg/dL)	25.64 ± 2.38	72.95 ± 6.98^###	41.55 ± 4.37^**	29.48 ± 2.1^***	28.59 ± 3.20^***
VLDL (mg/dL)	10.38 ± 1.9	24.55 ± 1.79^###	14.17 ± 1.43^**	11.67 ± 1.51^***	13.41 ± 0.761^**

^#p <0.05; ^##p <0.01; ^###p <0.001; NS, not significant when control versus FRU. *p <0.05, **p <0.01, ***p <0.001; ns, not significant when FRU versus FRU+CG200, FRU+CG400 and FRU+MET.

Oral glucose tolerance test (OGTT)

FRU-fed rats depicted an impaired clearance of exogenous glucose as indicated by high AUC_glucose (44.78%) compared to control rats. FRU+CgE (200 and 400) groups were efficient in clearing circulating glucose load and hence showed a significant decrement (p <0.05) in AUC_glucose values (30.82% and 40.9%). FRU+MET group also showed a significant decrement (p <0.05) in AUC_glucose (39.16%) value (Figures 1 & 2).

Figure 1.  Effect of C. glandulosum Coleb. and metformin on oral glucose tolerance test (OGTT).

Figure 2.  Effect of C. glandulosum Coleb. and metformin on area under curve during oral glucose tolerance test (OGTT). ^#p <0.05; ^##p <0.01; ^###p <0.001; NS, not significant when control (CON) versus FRU. *p <0.05; **p <0.01; ***p <0.001; ns, not significant when FRU versus FRU+CG200, FRU+CG400 and FRU+MET.

Measurement of blood pressure by invasive (direct) method

FRU-fed rats demonstrated significant increment (p <0.05) in mean arterial blood pressure (MABP; 22.72%) as compared to control rats. There was a dose-dependent decrement (p <0.05) in MABP (12.9% and 18.18%) in FRU+CgE (200 and 400) groups as compared to FRU-fed rats (Figure 3). FRU+MET group also showed significant decrement (p <0.05) in MABP (16.23%).

Figure 3.  Effect of C. glandulosum Coleb. and metformin on mean arterial blood pressure. ^#p <0.05, ^##p <0.01, ^###p <0.001 and NS, not significant when control (CON) versus FRU. *p <0.05; **p <0.01; ***p <0.001; ns, not significant when FRU versus FRU+CG200, FRU+CG400 and FRU+MET.

Vascular reactivity to adrenaline and phenylephrine

Blood pressure response to adrenaline (AD) and phenylephrine (PH) were significantly increased in FRU-fed rats (63.72% and 66.7%) as compared to control rats. FRU+CgE (200 and 400) groups showed a significant decrement (p <0.05) in pressure response to AD (39.04% and 53.98%) and PH (39.59% and 50.64%) as compared to FRU-fed rats (Figures 4A, 4B). These results were similar and comparable to that of the FRU+MET group.

Figure 4.  Effect of C. glandulosum Coleb. and metformin on vascular reactivity. ^#p <0.05, ^##p <0.01, ^###p <0.001; NS, not significant when control (CON) versus FRU. *p <0.05, **p <0.01, ***p <0.001; ns, not significant when FRU versus FRU+CG200, FRU+CG400 and FRU+MET.

Vascular reactivity to acetylcholine and isoprenaline

Blood pressure response to acetylcholine (AC) and isoprenaline (IS) were significantly decreased in FRU-fed rats (65.7% and 62.08%) as compared to control rats. FRU+CgE (200 and 400) groups recorded a significant increment (p <0.05) in pressure response to AC (55.45% and 64.67%) and IS (60.88% and 69.05%) as compared to FRU-fed rats (Figures 4C, 4D). These results were similar and comparable to that of the FRU+MET group.

Histopathology of liver

There were no degenerative or inflammatory changes observed in the photomicrograph of the liver histology of the control and experimental groups. Also, there were no major differences in the histoarchitecture of the central vein or hepatocytes as their cellular boundaries appeared to be integral and without any major distortions (Figure 5).

Figure 5.  Photomicrograph of liver from control (CON), fructose (FRU), FRU+CG200, FRU+CG400 treated groups (100X).

Discussion

The increasing trend in consumption of the western diet has resulted in a considerable rise in the dietary FRU intake. Recent evidence from epidemiological and biochemical studies clearly indicates high intake of dietary FRU as an important causative factor in the development of MetS (Basciano et al., 2005). It has been established that a fructose-rich diet induces insulin resistance, hyperinsulinemia, hypertrigylceridemia and MetS in humans (Le & Tappy, 2006) and experimental rats (Basciano et al., 2005). Hence, in the present study, insulin resistance, hypertriglyceridemia and hypertension were induced by feeding a fructose-rich diet to laboratory rats.

Fructose metabolism in liver bypasses the regulatory phosphofructokinase step in glycolysis and in turn activates pyruvate dehydrogenase which favors esterification of fatty acids leading to increased VLDL secretion (Mayes, 1993), resulting in high plasma LDL levels. Dietary FRU is also known to induce hypertriglyceridemia (Zavaroni et al., 1982) mainly due to both an increased secretion from liver and decreased clearance of VLDL in plasma (Mayes et al., 2004). Excess VLDL secretion has been known to deliver high amounts of FFA and TG to muscle and other tissues leading to development of insulin resistance (Zammit et al., 2001). LDL particle size has been found to be inversely related to TG concentration (Edwards et al., 2001) and therefore higher TG results in formation of smaller, denser and more atherogenic LDL particles. In the present study, FRU-fed rats recorded elevated levels of TG, VLDL and LDL along with low HDL, a condition characteristic of atherogenic dyslipidemia in MetS (Grundy, 2006). C. glandulosum treatment to FRU-fed rats significantly elevated HDL and lowered TG, VLDL and LDL, thus improving atherogenic risk factors.

In recent years, adipose tissue has been highlighted by many studies as a key player in insulin resistance (Karpe & Tan, 2005). Elevation in plasma FFA levels during obesity and type II diabetes mellitus is suggested to be occurring due to a high rate of escape of FFA from esterification in adipose tissue rather than impaired insulin action (Hwang et al., 1987). Such a condition results in hypertriglyceridemia due to increased output of FFA by adipose tissue and by providing excess fatty acids to liver for TG synthesis (Cummings, 1988) thus, epitomizing hypertriglyceridemia as an important marker of insulin resistance (Willett, 2002). FRU-fed rats depicted elevated level of plasma FFA and an impaired glucose tolerance whereas, C. glandulosum treatment to FRU-fed rats lowered plasma FFA and TG levels indicating its protective role against development of insulin resistance.

OGTT represents a simple method that has gained widespread use (Ahren & Pacini, 2004) to indirectly assess the in vivo peripheral insulin action and insulin resistance in animals (Liou et al., 2002) and humans (Cox et al., 2004). OGTT was therefore evaluated in the present study to determine the effect of C. glandulosum on insulin resistance. We could observe that insulin-stimulated disposal of ingested glucose into peripheral tissue was markedly reduced in FRU-fed rats, as was reflected by higher AUC_glucose values, whereas, marked reduction in AUC_glucose values of FRU+CgE-treated rats indicates improved peripheral glucose utilization. It can be speculated that these changes may be due to improved insulin sensitivity of peripheral tissues as reported in other studies using synthetic drugs and natural medicines (Ramin et al., 1996; Attele et al., 2002).

It has been well documented that in FRU-fed rats, insulin receptor mRNA and insulin receptor numbers in skeletal muscle and liver were significantly lower as compared to rats fed with regular laboratory diet (Catena et al., 2003). We observed elevation in plasma insulin titer, along with mild hyperglycemia and subsequent high FIRI value in FRU-fed rats. However, FRU+CgE fed rats recorded significantly lowered fasting blood glucose, plasma insulin and FIRI thus preventing hyperinsulinemia, a key risk factor in MetS.

Blood pressure elevation is known to contribute to diabetic microvascular and macrovascular complications (Fineberg, 1999; Bakris et al., 2000). Most patients with concomitant hypertension and diabetes require more than one agent to attain adequate blood pressure control. FRU-induced hypertension is developed as a result of hyperinsulinemia, insulin resistance and hypertriglyceridemia (Rosen et al., 1997). Hyperinsulinemia is further known to activate the sympathetic nervous system resulting in elevation of blood pressure (Hwang et al., 1987) and therefore, high blood pressure recorded in FRU-fed rats is in accordance with a previous report (Balaraman et al., 2006). FRU+CgE-fed rats recorded a significant decrement in vasoconstrictor response when challenged with AD and PH whereas, the vasorelaxant response in the same experimental group was increased when challenged with AC and IS coupled with a decrease in MABP. Thus, hypotensive action of C. glandulosum could have resulted due to improved insulin resistance in FRU+CgE groups.

Histopathological features of liver and activity levels of plasma AST and ALT did not record any major alterations in control and experimental rats. These results suggest that neither FRU feeding nor extract/drug treatment manifests any structural or functional alterations in liver function.

C. glandulosum exerts protective effect against experimentally induced MetS by bringing about corrective pharmacological changes in plasma lipid profile, lowering plasma glucose and insulin and improving insulin resistance. Studies of isolation of active compound(s) from C. glandulosum and its mode of action in improving insulin resistance need further scrutiny.

Conclusion

This is the first scientific report on potential of C. glandulosum in controlling various metabolic discrepancies associated with MetS. Thus, the potential therapeutic use of C. glandulosum in controlling MetS is indicated.

Acknowledgement

The authors are grateful to Prof. R. Balaraman, Department of Pharmacy, Faculty of Technology and Engineering, the M.S. University of Baroda, for providing facilities for blood pressure measurement.

Declaration of interest

The authors (J.R.N., T.M.C. and Ansarullah) are grateful to the University Grants Commission, New Delhi for providing Financial Assistance in the form of Junior research fellowship in science for meritorious students (JRFSMS)scholarship.