INTRODUCTION:

The blood pressure is the product of cardiac output and total peripheral resistance; Blood Pressure = CO X TPR. While the CO=SV X HR, where SV stands for the stroke volume and the HR for heart rate.

The mechanisms of blood pressure control can be divided according to how rapid they act in response to pressure changes into:

a) Rapidly Acting Mechanisms: Nervous Regulation of Circulation.

b) Long–Term Mechanisms for Arterial pressure Regulation or the Renal-Body fluid System for Arterial Pressure Control.¹

Rapidly Acting Pressure Control Mechanisms or the Nervous Regulation of the Circulation:

The mechanism by which the nervous system controls the circulation is almost completely through the autonomic nervous system, which exerts its effect mainly through the sympathetic nervous system. While the parasympathetic nervous system has less vital role in this field².

Long-Term Mechanism for Arterial pressure: The Renal-Body Fluid System for Arterial Pressure Control which entails a simple mechanism: When the extracellular fluid becomes more, the arterial pressure increases. The rising pressure in turn has induces the kidneys to excrete the excess extracellular fluid, thus shifting pressure back to normal³.

The consequences of the actual level of pressure in a given person will depend not only on the measured level but also upon certain ‘risk’ factors such as age, race, genetic inheritance gender, stress, diet, obesity, glucose tolerance, cholesterol, alcohol consumption and smoking habits⁴.

The prevalence of high blood pressure increases with age. High blood pressure, an extremely common health problem in geriatric population, afflicts approximately two thirds of the population after the age of 65 year⁵. In Iraq the population based survey on hypertension was conducted in 2013 and it has shown the prevalence of 44%⁶. Prevalence of hypertension is affected by the ethnic composition of the population studied and the criteria implemented to assess the condition. White suburban population presents nearly with one-fifth of individuals having blood pressure >160/95 mmHg, while almost one-half with pressures >140/90 mmHg. Blacks show a higher prevalence of hypertension than whites (38% versus 29%)⁷.

The prevalence of secondary hypertension is about 10% of patients presenting with hypertension⁸. However, the percentage is reported to be as high as 35% in referral centers where patients undergo extensive evaluation⁹.

Medicinal plants:

Hibiscus subdarrifa (Rossele):

Chemical Constituents:

The dried calyces contain flavonoids hibiscetine, gossypetine, and sabdaretine. Moreover, it contains anthocyanin, delphinidin 3-monoglucoside, thiamine, riboflavine, niacin, ascorbic acid, cyanidin¹⁰.

Medicinal Uses:

Astringent; Diuretic; Stomachic. Roselle is an aromatic, astringent, cooling herb that is much used in the Tropics. It is said to have diuretic effects, to help in lowering fevers¹¹. The leaves are emollient, diuretic, refrigerant, and sedative. The flowers contain gossypetin, anthocyanin, and the glycoside hibiscin. These may have diuretic effects and stimulating intestinal peristalsis¹².

Plantago major (Plantain):

Chemical Constituents: Iridoids; aucubin,3,4-dihydroaucubin, 6-o-b-glucosylaucubin, catalpol. Flavonoids; apigenin, lutelin, scutellarin, baicalein, nepetin, hispidulin, plantagoside¹³.

Medicinal Uses:

Antidote; astringent; demulcent; diuretic; expectorant; haemostatic; laxative; ophthalmic; poultice; refrigerant¹⁴.

Teucrium polium (Polion):

Chemical Constituents:

Beta-sitosterol, stigmasterol, campesterol, brassicasterol and clerosterol, flavinoids, glucose, fructose, raffinose and rhamnose¹⁵.

Medicinal Uses:

Teucrium polium is widely used by the folk-medicine practitioners in Saudi Arabia for the treatment of inflammations, rheumatism, diabetes and ulcers. The presence of flavonoids and sterols might be responsible for the anti-inflammatory activity¹⁶. Also another study proved that the aqueous extract of Teucrium polium reduced significantly the serum levels of cholesterol and triglycerides in hyperlipidemic rats¹⁷. Mild hypotensive effect was reported by one study¹⁸

AIMS OF THE STUDY:

1. To assess the antihypertensive efficacy of the medicinal plants used.

2. Investigating the mechanisms of actions of tested agents.

MATERIALS AND METHODS:

The study protocol was approved by the Scientific and Ethical Committee in Alkindy College of Medicine/ University of Baghdad.

Forty-two healthy local domestic rabbits of male sex were used in this study, weighing (1000-1200gm). They were supplied by the animal house of College of Medicine/Al-Nahrain University. These animals were kept in cages with a wire mesh in the floor. All the animals received oxoid pallet diet with water ad libitum.

Hypertension was induced in experimental rabbits with phenylephrine 0.2mg/kg i.v. with increasing the dose (until Blood pressure>130/90mmHg). All of the tested agents used in group one were applied to the animals at 9.00 A.M. The animals were divided into 7 groups (each group contained 6 rabbits):

Group A: Was daily treated with 2ml of normal saline orally once daily as a control group.

Group B: Was daily treated with 0.85mg/kg of atenolol orally once daily as a treatment control.

Group C: Was daily treated with 0.6mg/kg of furosemide orally twice daily as a treatment control.

Group D: Was daily treated with 0.15mg/kg of candesartan orally once daily as a treatment control.

Group E: Was daily treated with 0.5mg/kg of the aqueous extract of Hibiscus subdariffa orally once daily as a test.

Group F: Was daily treated with 1mg/kg of the aqueous extract of Plantago major orally once daily as a test .

Group G: Was daily treated with 50mg/kg of the aqueous extract of Teucrium polium orally once daily as a test.

The parameters were recorded every hour for the duration of 8 hours (except for the urine output which was measured at the end of the 8th hour).

Parameters:

1. Systolic blood pressure (SBp).

2. Diastolic blood pressure (DBp).

3. Heart rate. By microphone transducer.

4. Urine output (collected by urethral catheter+ graduated cylinder) measured per 8 hours.

5. Blood flow (flow meter). By microphone transducer

The Tested Agents: Table 1.

Table 1: The tested agents (drugs and extracts of medicinal plants).

Drugs
Name	Manufacturer	Preparation
Atenolol (Vascoten)	Medochemie Ltd, Limassol, Cyprus	Tablets (each tablet contains 50 mg) crushed & dissolved in 58ml distilled water with shaking.
Hydrocortisone sodium succinate	Troge Medical GMBH, Hamburg Germany	(Each vial contains 100mg). Dissolved in 100ml distilled water with shaking.
Candesartan cilexitel	AstraZeneca group of companies, Sweden	Tablets (each tablet contains 16mg). crushed & dissolved in 106ml distilled water with shaking.
Furosemide	Holden Medical BV, Netherland	Tablets (each tablet contains 40 mg). crushed & dissolved in 66ml distilled water with shaking.
Hypertonic saline 5%		Prepared by the addition of 5 gm of Nacl to 100 ml of distilled water with shaking.
Phenylephrine hydrochloride	BDH chemicals Ltd, Poole England	(container contains 100 gm). Prepared by adding 20mg to 100ml distilled water to get the desired concentration 0.2mg/ml.
Pentobarbital sodium	Batch lab. Renaudine, France	vial contains 60mg/ml.
Extracts of medicinal plants
Hibiscus subdariffa		The aqueous extract of the dried calices was used in this study in 0.5 mg/kg concentration
Plantago major		The aqueous extract of Plantago major leaves was used in this study in 1mg/kg concentration.
Teucrium polium		The aqueous extract of Teucrium polium flowers was used in this study in 50 mg/kg concentration

Aqueous extraction of the medicinal plants:

Ten gram of the well grinded medicinal plant were taken and mixed to 100ml of distilled water by the use of electric mixing machine for 15 minutes, and then the mixture was put in a hot plate magnetic stirrer for 48 hours in temperature of 45-50˚C continuously. Then the solution was centrifuged at 6000RPM for 30 minutes. We discarded the sediment and took the supernatant. We have repeated the procedure three times to ensure the discharge of sediment, then the supernatant was filtered by use of seitz filter (with pore diameter of 0.45μm). The supernatant was collected in dark container to avoid the effect of light.

Methodology:

1 Anesthesia: For all of the procedures bellow, the animals have been anaesthetized with pentobarbital in a dose of 30mg/kg i.p¹⁹.

2 By infusing phenylephrine 0.2mg/kg i.v., increase the dose (until Blood pressure>130/90mmHg)²⁰.

3 Blood pressure measuring (indirect method): Microphone transducer applied on the medial aspect of the left thigh fixed to a constant tightness and connected to grass polygraph²¹.

4 Heart Rate Measuring: The microphone transducer was used for the measurement of the peripheral pulse rate²²

5 Measuring urine output: Urine output is collected to an accurate graduated cylinder by polythene catheter inserted into the urinary bladder. The first urine before treatment is voided out of cylinder²¹

6 Measuring blood flow: Fascias, muscles above the femoral artery are removed aside, and then a small arterial blood flow probe is inserted carefully around the femoral artery²³.

Method of statistical analysis Student pooled t-test and ANOVA was used to estimate the significant difference between groups with Dennett’s at (P < 0.05). Graph pad prism program was used for that purpose.

RESULTS:

Each figure presents the different values of the tested agents for certain parameter as compared with the control. The changes in the studied parameters is discussed in the illustrated graphs below.

The effects of tested agents on systolic blood pressure is presented in figure 1. There is a lowering effect with a statistical significance for atenolol, furosemide and candesartan.

Figure 1: The systolic blood pressure of the tested agents. *=p<0.05, **=p<0.01, ***=p<0.001.

While the effect of tested agents on diastolic blood pressure is presented in figure 2. There is a lowering effect with a statistical significance for atenolol and candesartan.

Figure 2: The diastolic blood pressure of the tested agents. *=p<0.05, **=p<0.01, ***=p<0.001.

The effect of tested agents on heart rate is presented in figure 3. there is an lowering effect with atenolol and with a statistical significance and increasing effect with furosemide, candesartan, Hibiscus subdariffa, Plantago major and Teucrium polium with a statistical significance.

Figure 3: The effect of the tested agents on heart rate. *=p<0.05, **=p<0.01, ***=p<0.001.

The effect of the tested agents on blood flow I illustrated in figure 4. Atenolol shows a lowering effect with a statistical significance while candesartan has an increasing effect with a statistical significance.

Figure 4: The effect of the tested agents on heart rate as compared to the control. *=p<0.05, **=p<0.01, ***=p<0.001.

While concerning the urine output the results are shown in figure 5. Both furosemide and Hibiscus subdariffa has an increasing effect with a statistical significance.

Figure 5: The effect of the tested agents on urine output. *=p<0.05, **=p<0.01, ***=p<0.001.

DISCUSSION:

In the present study, hypertension model was induced using phenylephrine injection²⁴, to simulate the type of hypertension caused by increased peripheral vascular resistance mainly due to vasoconstriction with some more acute course than that seen in the first model. It is important to mention that the normal rabbit blood pressure is about 104±4/78±3 mmHg²⁵. While normal heart rate is about 240beat/min²⁶. Normal urine output is 112ml/day. We should notice that there is biologic variations between these animals. Furosemide is a potent loop diuretic that is mostly effective on such hemodynamic disturbances. All diuretics initially lower blood pressure by raising urinary sodium excretion and/or decreasing plasma volume, cardiac output and extracellular fluid volume, Then, these parameters return back to normal. After this point, the lowered blood pressure is related to a decrease in total peripheral resistance, thereby compensating for the underlying hemodynamic defect of hypertension. The underlying mechanism which is responsible for declining peripheral resistance involve decreased sensitivity of blood vessels to sodium or potassium channel activation²⁷.

Phenylephrine, which is an α 1 -selective agonist so the main cause of hypertension is merely peripheral vasoconstriction leading to increased peripheral vascular resistance. Furosemide is not significantly effective in lowering blood pressure due to the initial increasing urinary sodium excretion, but the reduction in plasma volume, and cardiac output exerted by furosemide was not sufficiently enough to overcome the hypertensive effect of phenylephrine. Indeed, systemic vascular resistance sometimes increases in response to loop diuretics. This effect has been attributed to transient activation of systemic or intravascular RAS (rennin angiotensin system)²⁸.

Hibiscus subdariffa has shown no significant effect on the parameters used in the study. This is because that the method of induction was different and involves the use of phenylephrine and although that extract of Hibiscus subdariffa has both vasodilator and diuretic activity, it was not enough to overcome the potent vasoconstriction induced by phenylephrine. In addition, this finding contrasts with that of another study done in USA and can be explained by different routes of administration since they used the intravenous route in their study²⁰.

Hibiscus subdariffa is significantly effective in increasing urine output as it contains flavonoids²⁹.

Plantago major has shown no significant effect on the parameters implemented in the study. This coincides with results of another study conducted in Vietnam³⁰.

Teucrium polium it showed no significant effect on the parameters of the study.

CONCLUSIONS:

The aqueous extract of Hibiscus subdariffa is highly effective as a diuretic agent, however, it is not effective as antihypertensive agent at the concentration mentioned. Its action involves diuretic and vasodilator effect. While aqueous extracts of Plantago major and Teucrium polium are not effective as antihypertensive drugs at the concentrations mentioned.

ACKNOWLEDGMENT:

We would like to thank Dr. Areege Kamal for her efforts in finalizing this manuscript.

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Received on 28.11.2020 Modified on 30.12.2020

Research J. Pharm. and Tech. 2021; 14(9):4832-4836.

DOI: 10.52711/0974-360X.2021.00839