INTRODUCTION:

Globally, high blood pressure is estimated to cause about 13% of the total deaths¹.Developing countries are increasingly faced with the double burden of hypertension and other cardiovascular diseases². Hypertension places an excessive financial burden on populations and health systems, consuming scarce resources³.Herbal products are becoming increasingly popular, for the management of hypertension and other cardiovascular diseases, probably due to the fact that they are relatively cheaper. Sansevierialiberica is one of such plants with a potential for use in the management of hypertension.

Sansevierialiberica belongs to the family Agavaceae, and is one of the bow string hemp species⁴, with concave, short petioled leaves that are in part transversely banded with light and dark green striations⁵.

It has long rhizomes with long fibrous roots and a rapid rate of growth. It is grown as ornamental plants⁶, and is widely distributed throughout the tropics. Its leaves are very rich in fibers^7,8, protein⁸, potassium, calcium, magnesium, vitamin C, biotin, and riboflavin⁹. The leaves also contain alkaloids, allicins, carotenoids, flavonoids, glycosides, saponins and tannins^8,10. In traditional health care practice, the leaves are used as pain killers, and in the treatment of small pox, chicken pox, measles and most venereal diseases. The pressed juice of the leaves is dropped in the eyes and ears for the treatment of infections and inflammations. The fumes from the burning leaves are inhaled to relieve feverish headaches and cold. A decoction of the roots is drunk as a remedy for convulsions and as a vermifuge. In Nigeria, the leaves and roots of Sansevierialiberica are used in traditional health care practice for the treatment of asthma, abdominal pains, colic, diarrhea, eczema, gonorrhea, hemorrhoids, hypertension, diabetes mellitus, menorrhagia, piles, sexual weakness, wounds of the foot, and alleviating the effects of snake bites^7,11^-14. Ikewuchi and Ikewuchi¹⁵ reported the potential of the leaves’ protein to support the growth of Wistar rats. The hypotensive effect of aqueous extract of the leaves¹⁶, and their ability to moderate hematological indices and plasma chemistry in salt-loadedrats¹⁷, and hematology, plasma biochemistry and ocular indices of oxidative stress in alloxan-induced diabetic rats¹⁸have been reported. The Hypoglycemic, hypocholesterolemic, anti-anemic and ocular-protective¹⁹ and hepatoprotective²⁰ effects of the aqueous extract of the rhizomes have also been reported.

Earlier, gas chromatographic analysis of aqueous extract of the rhizomes revealed the presence of twenty nine known flavonoids (consisting mainly of apigenin, quercetin, kaempferol, naringenin, (-)-epicatechin, biochanin, (+)-catechin, diadzein, ellagic acid andbutein), thirty nine known alkaloids (consisting mainly of akuamidine, voacangine and echitamidine), tannic acid and β-sitosterol^19,²⁰.The present study reports the time course of the effects of an aqueous extract of the rhizomes of Sansevierialiberica Gerome and Labroy on the blood pressure indices and pulse rates of normal and sub chronic salt-loaded Wistar rats.

MATERIALS AND METHODS:

Preparation of plant extract: Samples of fresh whole Sansevierialiberica plants were procured from a horticultural garden by Air Force Gate, Aba Road, Port Harcourt, and another at the University of Port Harcourt’s Abuja campus, Port Harcourt, Nigeria. They were duly identified by Dr. Michael C. Dike of Taxonomy Unit, Department of Forestry and Environmental Management, Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria; and Mr. John Ibe, the Herbarium Manager of the Forestry Department, National Root Crops Research Institute, Umuahia, Nigeria. The rhizome was removed, clean of soil, oven dried at 55 °C and ground into powder. The resultant powder was soaked in hot, boiled distilled water for 12 h, after which the resultant mixture was filtered and the filtrate was stored in the refrigerator for subsequent use. A known volume of this extract was evaporated to dryness, and the weight of the residue used to determine the concentration of the filtrate, which was in turn used to determine the dose of administration of the extract.

Experimental design the antihypertensive study:

Wistar albino rats (weighing 180-210 g at the start of the study) were collected from the animal house of the Department of Physiology, University of Nigeria, Enugu Campus. Studies were conducted in compliance with applicable laws and regulations for handling experimental animals. The rats were weighed and sorted into seven groups (Table 1) of five animals each, so that their average weights were approximately equal. The animals were housed in plastic cages. After a 1-week acclimatization period on guinea growers mash (Port Harcourt Flour Mills, Port Harcourt, Nigeria), their weights and baseline blood pressures indices were taken, before commencing the experiment. Hypertension was induced by giving 8% salt-loaded feed for six weeks, to the appropriate rats. The 8% salt-loaded regimen was adapted from Obiefuna et al.²¹, Ikewuchi et al.^{22, 22,24,25} and Ikewuchi²⁶. At the end of six weeks, their weights and blood pressure indices were taken, before commencing administration of the extract. The Moditen^TM (amyloride hydrochloride-hydrochlorothiazide; product of Greenfield Pharmaceutical Co. Ltd, Jiang Su Province, China) and the extract were orally administered daily, for ten days. The dosages of administration of the extracts were adopted and modified from Ikewuchi and Ikewuchi¹⁹ and Ikewuchi et al.²⁰. The animals were allowed food and water ad libitum. The blood pressures and pulse rates were measured on days 5 and 10, after administration.

Table 1 Experimental design for the anti-hypertensive screening

S/N	ID	Treatment
1	Normal	Normal feed and water
2	Test control	8% salt-loaded feed and water
3	Reference	8% salt-loaded feed and moduretic (0.1 mg/kg body weight)
4	Treatment 1	8% salt-loaded feed and extract (100 mg/kg)
5	Treatment 2	8% salt-loaded feed and extract (200 mg/kg)
6	Treatment control 1	Normal feed and extract (100 mg/kg)
7	Treatment control 2	Normal feed and extract (200 mg/kg)

Determination of blood pressure and pulse rate of the rats:

The systolic and diastolic blood pressures and the pulse rate of the rats were measured via femoral pulse, using Omron RX Classic^TM sphygmomanometer (OMRON Healthcare UK, LTD). The pulse pressure and mean arterial pressure were calculated mathematically from systolic and diastolic blood pressures as earlier reported by Ikewuchi et al.^23,24,25, using the following formulae.

Pulse pressure= Systolic pressure- Diastolic pressure

Systolic pressure- Diastolic pressure

Mean arterial = Diastolic + ----------------------------------------------

pressure pressure 3

Statistical analysis of data:

All values are reported as the Mean± S.E.M. (standard error in the mean). The values of the variables were analysed for statistically significant differences using the Student’s t-test, with the help of SPSS Statistics 17.0 package (SPSS Inc., Chicago Ill). P<0.05 was assumed to be significant. Graphs were drawn using Microsoft Office Excel, 2010 software.

RESULTS:

The time course of the effect of aqueous extract of the rhizomes of Sansevierialiberica on the systolic blood pressure of normal and sub chronic salt-loaded rats is given in Figure 1. At baseline, the systolic blood pressure of the test control group was significantly lower (P<0.05) than that of treatment 1, but not significantly different from the other groups. On a day 0, the systolic blood pressure of the test control group was significantly higher (P<0.05) than those of the normal and treatment control 1 groups, but not significantly different from those of the other groups. On day 4, the systolic blood pressure of the test control group was significantly higher (P<0.05) than those of the groups, except that of treatment 2. On day 8, the systolic blood pressure of the test control group was significantly higher (P<0.05) than those of all the other groups. Compared to corresponding values on day 0, the systolic blood pressure of the reference treatment (on days 4 and 8), treatment 1 (days 4 and 8), and treatment 2 (on day 4) were significantly lower (P<0.05).

Figure 2 shows the time course of the effect of aqueous extract of the rhizomes of Sansevierialiberica on the diastolic blood pressure of normal and sub chronic salt-loaded rats. At baseline, the diastolic blood pressure of the test control group was not significantly different from those of the other groups. On a day 0, the diastolic blood pressure of the test control group was significantly higher (P<0.05) than those of the normal and treatment control 2 groups, but not significantly different from those of the other groups. On day 4, the diastolic blood pressure of the test control group was significantly higher (P<0.05) than those of the groups. On day 8, the diastolic blood pressure of the test control group was significantly higher (P<0.05) than those of all the other groups, except reference and treatment 2. Compared to corresponding values on day 0, the diastolic blood pressure of the reference treatment (on day 4) was significantly lower (P<0.05), while that of the test control (on day 4) was significantly higher (P<0.05).

The time course of the effect of aqueous extract of the rhizomes of Sansevierialiberica on the pulse pressure of normal and sub chronic salt-loaded rats is given in Figure 3. At baseline, the pulse pressure of the test control group was not significantly different from the other groups. On a day 0, the pulse pressure of the test control group was significantly lower (P<0.05) than those of the treatments 1 and 2 groups, but not significantly different from those of the other groups. On day 4, the pulse pressure of the test control group was not significantly different from those of the groups. On day 8, the pulse pressure of the test control group was significantly higher (P<0.05) than those of treatment control 1 and 2 groups, but not significantly higher than those of the other groups. Compared to corresponding values on day 0, the pulse pressures of treatment 1 (days 4 and 8) and treatment 2 (on days 4 and 8) were significantly lower (P<0.05).

Figure 4 shows the time course of the effect of aqueous extract of the rhizomes of Sansevierialiberica on the mean arterial pressure of normal and sub chronic salt-loaded rats. At baseline, the mean arterial pressure of the test control group was not significantly different from those of the other groups. On a day 0, the mean arterial pressure of the test control group was significantly higher (P<0.05) than those of the normal and treatment control 1 and 2 groups, but not significantly different from those of the other groups. On day 4, the mean arterial pressure of the test control group was significantly higher (P<0.05) than those of all the groups. On day 8, the mean arterial pressure of the test control group was significantly higher (P<0.05) than those of all the other groups, except treatment 2. Compared to corresponding values on day 0, the mean arterial pressure of the test control group (on day 4) was significantly higher (P<0.5), while those of the reference treatment (on day 4) and treatment 1 (on day 4) were significantly lower (P<0.05)

The time course of the effect of aqueous extract of the rhizomes of Sansevierialiberica on the pulse rates of normal and sub chronic salt-loaded rats is given in Figure 3. At baseline, the pulse rate of the test control group was not significantly different from those of the other groups. On a day 0, the pulse rates of the test control group was significantly lower (P<0.05) than that of the treatment control 1 group, but not significantly different from those of the other groups. On day 4, the pulse rates of the test control group was significantly lower (P<0.5) than those of the normal, reference treatment and treatment 2 groups, but not significantly different from those of the groups. On day 8, the pulse rates of the test control group was not significantly different from those of the other groups. Compared to corresponding values on day 0, the pulse rates of the normal (on day 4), test control (on day 8), reference treatment (on day 8), treatment control 1 (day 4) and treatment control 2 (on days 4 and 8) were significantly higher (P<0.05), while test control (on day 4) was significantly lower (P<0.05).

The time course of the effect of aqueous extract of the rhizomes of Sansevierialiberica on the percentage reductions in systolic blood pressure indices and pulse rates of normal and sub chronic salt-loaded rats is given in Table 2. On day 4, the percentage reduction in the systolic pressure of the test control group was significantly lower (P<0.05) than those of treatments 1 and 2, but not different from those of the normal, reference treatment, and treatment controls 1 and 2. On day 8, the percentage decrease in the systolic blood pressure of the test control group was significantly lower (P<0.05) than those of the other groups, except the normal group. On day 4, the percentage decrease in diastolic blood pressure of the test control group was significantly lower (P<0.05) than those of the reference treatment, treatment 2 and treatment control 1, but not significantly different from that of the other groups. On day 8, the percentage decrease in diastolic blood pressure of the test control group was not significantly different from those of the other groups. On day 4, the percentage decrease in pulse pressure of the test control group was significantly lower (P<0.05) than that of treatment 1, but not significantly different from those of the other groups. On day 8, the percentage decrease in pulse pressure of the test control group was significantly lower (P<0.05) than those of treatment 2 and treatment control 2 groups, but not significantly different from those of the other groups. On day 4, the percentage decrease in mean arterial pressure of the test control group was significantly lower (P<0.05) than those of the reference treatment, and treatments 1 and 2, but not significantly different from those of the other groups. On day 8, the percentage decrease in the mean arterial pressure of the test control group was significantly lower (P<0.05) than those of the reference treatment, and treatment 1, but not significantly different from those of the other groups. On day 4, the percentage decrease in pulse rates of the test control group was significantly higher (P<0.05) than those of the normal, reference treatment and treatment 2, but not significantly different from those of the other groups. On day 8, the percentage decrease in pulse rates of the test control group was not significantly different from those of all the other groups.

Table 2 Effect of aqueous extract of the rhizomes of Sansevierialiberica on the percentage reduction in blood pressure indices and pulse rates of normal and sub chronic salt-loaded rats

Parameter	Magnitude (%)
Parameter	Normal	Test control	Reference	Treatment 1	Treatment 2	Treatment control 1	Treatment control 2
Systolic blood pressure
Day 4	-4.93±14.72^a	-2.14±6.84^a	26.00±14.22^a,b	34.60±8.87^b	19.01±9.60^b,c	11.77±20.83^a,c	2.58±19.13^a,c
Day 8	3.59±10.01^a,b	-4.45±5.48^a	20.74±11.74^b,c	26.60±12.37^c	10.43±11.61^b	8.26±3.70^b	19.18±18.06^b,c
Diastolic blood pressure
Day 4	-9.18±18.34^a,c	-6.44±3.03^c	23.80±18.16^b	20.77±26.10^a,b,c	13.97±17.12^a,b	21.05±17.95^a	4.02±24.96^a,c
Day 8	3.31±21.85^a	-2.72±10.36^a	19.23±22.59^a	11.68±31.31^a	-2.69±23.14^a	2.20±24.42^a	10.03±24.43^a
Pulse pressure
Day 4	0.92±32.13^a,b	6.13±31.20^a	17.84±53.76^a,b	46.18±10.39^b	26.59±10.46^a,b	-1.85±41.55^a,b	-6.04±24.03^a,b
Day 8	14.72±23.78^a,b	-10.88±28.94^a	11.25±28.07^a,b	38.46±14.01^a,b	32.29±6.79^b	12.06±39.73^a,b	29.76±28.79^b
Mean arterial pressure
Day 4	-7.24±15.23^a,c	-4.60±1.91^a	25.21±14.15^b	28.07±16.64^b,c	16.26±13.45^b,d	16.79±16.91^a,b,c	3.57±22.28^a,c,d
Day 8	-0.22±15.82^a,c	-3.37±6.97^a	20.36±16.84^b,c	19.79±19.06^b	3.17±17.92^a,b	5.18±14.15^a,b	14.29±20.80^a,b
Pulse rate
Day 4	-34.13±14.78^a	9.96±19.38^b	-50.52±37.05^a	-28.59±33.33^a,b	-39.85±27.63^a	-12.10±25.78^a,b	-10.27±22.46^a,b
Day 8	-7.29±13.27^a,c	-22.25±15.11^a,b,c,d	-55.88±43.78^b,d	-23.40±39.42^a,b,c,d	-12.25±23.79^a,b,c,d	7.94±18.18^a,b	-24.90±10.52^c,d

Values are mean ± s.d., n = 5, per group. ^a,^b,cValues in the same block group with different superscripts are significantly different at P<0.05.

Figure 1: Effect of aqueous extract of the rhizomes of Sansevierialiberica on the systolic blood pressure of normal and sub chronic salt-loaded rats.

Values are mean ± s.e.m., n = 5, per group. ^a,^b,cValues in the same block group with different superscripts are significantly different at P<0.05. *P<0.05 compared to the corresponding values on day 0.

Figure 2: Effect of aqueous extract of the rhizomes of Sansevierialiberica on the diastolic blood pressure of normal and sub chronic salt-loaded rats.

Figure 3: Effect of aqueous extract of the rhizomes of Sansevierialiberica on the pulse pressure of normal and sub chronic salt-loaded rats.

Figure 4: Effect of aqueous extract of the rhizomes of Sansevierialiberica on the mean arterial pressure of normal and sub chronic salt-loaded rats.

Figure 5: Effect of aqueous extract of the rhizomes of Sansevierialiberica on the pulse rates of normal and sub chronic salt-loaded rats.

DISCUSSION:

The hypotensive activity of the extract may be due to its contents of pharmacologically active compounds like kaempferol, quercetin, sitosterol and akuamidine, which have earlier been reported^19,20 to be present in the extract. According to Ogundaini et al. (1983, cited in ref. 27), β-sitosterol has hypotensive properties with little effect on the heart rate. Duarte et al.^[^28] reported that quercetin reduces elevated blood pressure, cardiac and renal hypertrophy and functional vascular changes in spontaneously hypertensive rats; while Ahmad et al.^[29], reported that kaempferol-3-O-rutinoside causes remarkable decrease in systolic, diastolic, mean arterial blood pressure and heart rate. Quercetin appears to exert its blood pressure-lowering effects by improving the health of the endothelium, the lining layer of the arteries that controls blood flow and pressure^30,31. Hirasawa and colleagues have also reported the antihypertensive activity of akuamidine³².

In this study, the extract moderated all the blood pressure indices, although the extent of moderation is different. The relative impact of blood pressure components (systolic blood pressure, diastolic blood pressure, pulse pressure and mean arterial pressure) on cardiovascular risk is currently under debate. Their contributions to cardiovascular disease change across the lifespan: from diastolic blood pressure to systolic blood pressure and ultimately to pulse pressure^33-36. The implication of this is that the extract may be useful for the management of hypertension and resultant cardiovascular complications, across all age groups. The present result supports the traditional use of the plant in the management of hypertension.

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Received on 31.07.2013 Modified on 20.10.2013

Research J. Science and Tech. 6(1): Jan.-Mar. 2014; Page 06-12