The leaves of Irvingia gabonensis were collected from the Herbarium Keeper of the Forestry Research Institute, Ibadan, Oyo State, Nigeria. A voucher specimen of the plant has been deposited with the Institute’s Herbarium under voucher number FHI 103947.

The plant leaves were obtained in large quantities and left to dry at room temperature for two days after which they were dried in an oven at 35 – 40^0C for 36 hrs. After that some of the leaves were ground into a coarse powder. The powdered leaves were kept in an air-tight glass container and stored in a dry place. 50g of the powder was extracted using Soxhlet apparatus for continuous extraction. The extracts (ethanol and water) were concentrated and dried under vacuum. The percent yield was 8.4% for ethanol extract and 0.82% for cold water extract.

Adult female wistar rats weighing 200-270g were obtained from the animal house of the department of Pharmacology/ Clinical Pharmacy, Faculty of Pharmaceutical Sciences, Ahmadu Bello University Zaria, Nigeria. They were maintained on Master feeds and water ad libitum. All experimental protocols were approved by the university animal ethic committee.

The adult female wistar rats weighing 200-250g were used for the study. They were injected intraperitoneally with diethylstilboesterol (1mg/kg) in order to induce a state of oestrous This was confirmed by histological examination of the vaginal smear.The rats were killed by a blow on the head and exsanguinated. The abdomen was opened and the uterine horns with attached fat and mesentery were surgically removed from both the right and left sides of the animal and placed in a Petri dish containing De Jallon’s solution of the following composition in millimole (mM): NaCl, 15.4; KCl,5.63; CaCl₂, 0.41; NaHCO₃, 5.95 and glucose 2.25.

The fat and mesentery were detached from the uterus and the latter was cut into left and right horns. Each uterine horn was mounted into an organ bath (20ml) under initial tension of 2g and contractions were measured isometrically using transducer (Ugo Basile) connected to a recording microdynamometer (7050). The preparation was allowed to equilibrate for 1hr before drugs were added.

Standard drugs (Ach, (5µg/ml), atropine (14nM), pirenzepine (0.1µM), and verapamil (0.1µM) and extracts were injected into the organ bath with syringe and needle to study their pharmacological effects. After the administration of each drug and/or extract, the tissues were washed three times, allowed to rest for two minutes before the addition of another drug or extract.To investigate the mechanism involved in the contraction of the uterus induced by the ethanol extract, pirenzepine an M₁ – muscarinic receptor antagonist, atropine (a non – specific muscarinic receptor antagonist) and verapamil (calcium antagonist) were used in the study. The latter was used to examine the involvement of extracellular calcium, added to the De Jallon solution and the tissue challenged with ethanol extract and acetylcholine.

The ileum of both male and female wistar rats was set up the same way except that the physiological solution used was Tyrode solution of the following composition in milimole (mM): NaCl, 137, KCl, 2.7; CaCl₂, 1.8; MgCl₂, 1.0; NaHCO₃, 11.0 and glucose 5.6. The rats were starved for 24hrs before the experiment commenced.

All values were expressed as mean ±SEM and results analysed using student’s t-test. P values less than 0.5% were taken to be statistically significant.

Fig. 1. Effect of Ach and Ethanol Extract of Irvingia gabonensis on non-pregnant rat uterus. Vertical bars represent Standard error of mean ±SEM

Figure 1

Fig. 1 shows the contractile effects of Acetylcholine (Ach) (0.5 – 20 µg/ml) and ethanol extract of irvingia gabonensis (25 - 100μg/ml) on the rat uterus. The contraction exhibited by the ethanol extract is similar to the agonistic effect of Ach on the rat uterine smooth muscle. Maximum contraction was obtained with 100μg/ml of the extract. The cold water extract showed no contractile effect on the uterus.

When the contractile effects of Ach and ethanol extract of I. gabonensis were challenged in the absence and presence of pirenzepine, atropine and verapamil, there was reduction in their effects. Atropine (14nM), a calcium channel blocker blocked the effect of the extract on the uterus by 90%.

Figure 2

In Fig. 2, Pirenzepine (0.1μM) an M₁-muscarinic receptor antagonist shifted the dose – response curve for the ethanol extract to the right but the maximum response to the extract was reproduced in the presence of this antagonist.

Figure 3

Fig. 3 shows the effect of verapamil in the absence and presence of verapamil. Verapamil (0.1μM) reduced the contractile effects of both acetylcholine (0.2 and 0.4 µg/ml) and ethanol extract (200 and 400 µg/ml) on the tissue by approximately 46 -56% and 61-90% respectively.