Introduction

For many years, hypertension has been globally recognised as the most prevalent cardiovascular disease with paramount complications such as coronary heart disease, stroke, sudden cardiac death, congestive heart disease, renal insufficiency and dissecting aortic aneurysm^1,2 The campaign to reduce cardiovascular disease has been aimed at treating hypertension since it a major tool in cardiovascular diseases³ . It has been estimated that approximately 25% of all prescribed medications today are of natural plant sources⁴. Rural dwellers in developing countries have attempted to control hypertension and its complications in the face of scarce socioeconomic resources by opting for herbal remedies^5,6,7. More scientific researches are needed to be done to verify the effectiveness and elucidate the safety profile of such herbal remedies.

Irvingia gabonensis (O’Rorke) baill Var. Excelsa⁸ is a species from the family of Irvingiaceae. It is a tropical forest tree mostly found in southern Nigeria, Sierra Leone and Equatorial Africa. The inedible fruit pulp is bitter and acrid although it can be eaten and has a turpentine flavour. The seeds are used as a source of human food and commonly known as Ogbono, a soup thickener in Igbo land of Nigeria. The seeds are rich in oil ( 54 – 67% ) calculated on dry kernel. This is known as “dika” fat which has been evaluated and used now as a tablet lubricant⁹. It has been reported that the seeds reduced fasting blood glucose levels in obese subjects¹⁰. The leaves are used in the treatment of dysentery and for wound dressing¹¹ and the stem bark for analgesic effects¹². The aqueous leaf extract of Irvingia gabonensis has been found to cause a significant dose-dependent decrease of gastrointestinal motility in mice¹³. Preliminary phytochemical screening of the aqueous leaf extract of Irvingia gabonensis revealed the presence of saponins, tannins, phenols and phlobatanins .

Irvingia gabonensis is largely used in both traditional and modern medicine for the treatment of several illnesses¹⁴. Cholesterol in the serum is a risk factor in coronary heart disease which is one of the complications of cardiovascular disease. No previous pharmacological work has been carried out to test the effect of this plant on blood pressure and as it has been reported that the seeds of Irvingia gabonensis reduced significantly the body weight and total cholesterol of obesed patients¹⁰, this study was therefore designed to determine the effect of ethanol leaf extract of Irvingia gabonensis on blood pressure of experimental animals.

Materials And Methods

Collection and preparation of plant material

Experimental procedure

Statistical Analysis

Results

The results of evaluating the effect of ethanol extract on cat blood pressure are shown in table 1 and 2. Different doses of the extract produced a fall in mean arterial blood pressure (MABP). This vasodepressor effect of ethanol extract was compared with that of acetylcholine using cat blood pressure. The mean arterial blood pressure (MABP) was 100mmHg. Intravenous administration of the ethanol extract produced a dose-related decrease in MABP with an EC50 of 1.08mg/kg and maximum fall (85.7mmHg) was obtained with 5mg/kg of the extract. There was a significant fall in MABP with the 5mg/kg extract (P<0.002).

Figure 1

Table. 1 Effect of different doses of leaf extract on cat blood pressure

Value represent mean ± SEM (n = 5), MABP before each injection was 100mmHg, *(P< 0.002)

Figure 2

Table 2 Dose related effect of atropine on the depressor action of Ach and ethanol extract of on cat blood pressure

Acetylcholine produced a maximum fall in MABP (71.4mmHg) when 0.2µg/kg was injected. Pre-treatment of the cat with atropine reduced the effects of both acetylcholine and ethanol extract on MABP (Table 2)

A low dose (2.5µg/kg) of atropine reduced the effect of the extract by 5mmHg and that of acetylcholine by 23mmHg, respectively. Atropine (5µg/kg) reduced the effect of acetylcholine and ethanol extract by 61mmHg and 76mmHg respectively. Propanalol injected before Ach or Ethanol extract did not reduce their depressor effects.

Discussion

The result of screening the effect of the ethanol extract of Irvingia gabonensis on the blood pressure of anaesthetized cats showed that the extract caused a reduction of the mean arterial blood pressure similar to the hypotensive response to Ach from a lower dose to a higher dose. This indicates that larger populations of the neurons may have been activated by the larger injection volume. The vasodilatatory effect of Ach^{15, 16} caused a reduction in the mean arterial blood pressure. These depressor effects were blocked by atropine an antimuscarinic agent. Propanalol, a classical β adrenoceptor blocker which decreases blood pressure as a result of decrease in cardiac output¹⁷ had no effect on the depressor effect of Irvingia gabonensis leaf extract. Furthermore, pre-treatment with Atropine reduced the fall in MABP by both the extract and Ach. This antagonism of the hypotensive effect of the extract by pre-treatment with atropine may possibly imply the involvement of muscarinic receptors by cholinergic mechanism. As has been reported that the seeds of this plant reduces total cholesterol¹⁰, this shows that this plant may also have likely properties in the management of hypertension as observed in this study. Further studies are needed to identify the effect of this extract in the treatment of other cardiovascular diseases. In conclusion, the ethanol leaf extract of Irvingia gabonensis showed a dose dependent hypotensive effect in cats which probably may have been mediated via the muscarinic receptors.