Raymond I. Ozolua

Possible mechanisms of action of the hypotensive effect of Annona muricata (soursop) in normotensive Sprague–Dawley rats

Context: Annona muricata Linn (Annonaceae) (soursop) is a food plant reported to have antihypertensive properties. Objective: We investigated the blood pressure reducing effect of its aqueous leaf extract and the possible mechanisms that may be responsible. Methods: Intravenous administration of an aqueous leaf extract (9.17–48.5 mg/kg) of A. muricata on the mean arterial pressure and heart rate were recorded invasively on anaesthetized, normotensive Sprague–Dawley rats. Contractile responses of rat aortic rings to the extract (0.5–4.0 mg/mL) were studied using standard organ bath techniques. Results: A. muricata (9.17–48.5 mg/kg) caused significant (p < 0.05) dose-dependent reduction in blood pressure without affecting the heart rates. The hypotensive effects were unaffected by atropine (2 mg/kg), mepyramine (5 mg/kg), propranolol (1 mg/kg) and L-NAME (5 mg/kg). A. muricata leaf aqueous extract significantly (p < 0.05) relaxed phenylephrine (10−9–10−4 M) and 80 mM KCl induced contractions in endothelium intact and denuded aortic rings; and caused a significant (p < 0.05) rightward shift of the Ca2+ dose response curves in Ca2+-free Kreb’s solution containing 0.1 mM EGTA. Conclusions: The hypotensive effects of A. muricata are not mediated through muscarinic, histaminergic, adrenergic and nitric oxide pathways, but through peripheral mechanisms involving antagonism of Ca2+.

In vitro determination of the uterine stimulatory effect of the aqueous leaf extract of Ficus exasperata

ETHNOPHARMACOLOGICAL RELEVANCE The leaves of Ficus exasperata Vahl (Moraceae) are used by traditional healers in Southern Nigeria to arrest pre-term contractions and are also used as an abortifacient in some parts of Africa. AIM OF STUDY An earlier study on the aqueous leaf extract of Ficus exasperata (AET) showed that the extract at lower concentrations inhibited oxytocin-induced uterine contractions and at higher concentrations, stimulated uterine contraction. This study thus aims to determine, the possible mechanisms by which AET stimulates uterine contraction in vitro. MATERIALS AND METHODS The contractile effect of AET (5.0 x 10(-2) to 100 x 10(-2)mg/ml) and oxytocin (which was used as a reference drug) were examined in the presence of the following antagonists: atropine (1.18 and 11.91 nM); indomethacin (1.42 and 14.25 nM); verapamil (2.03 and 20.35 nM); phentolamine (4.09 and 40.91 nM), or diphenhydramine (4.45 and 44.47 nM). The EC(50) and E(max) were determined and statistically analyzed using one-way ANOVA and Dunnett post hoc test. RESULTS There was no significant difference in the EC(50) and E(max) of AET and oxytocin in the presence of atropine. Diphenhydramine and phentolamine significantly inhibited (p<0.01) the extract but both drugs had no effect on oxytocin. However, significant differences (p<0.01) were observed in the EC(50) and E(max) of AET and oxytocin in the presence of verapamil and indomethacin. CONCLUSIONS These results suggest that the stimulation of uterine contractility by AET may arise from the activation of histamine H(1)- and/or alpha-adrenergic receptors, interference with calcium channels and/or stimulation of prostaglandin synthesis in utero.

Hypoglycemic activity of aqueous seed extract of Hunteria umbellata in normal and streptozotocin-induced diabetic rats.

The present study evaluated the aqueous seed extract of Hunteria umbellata K. Schum (Apocynaceae) for hypoglycemic activity in rats. Diabetes was induced by a single dose of streptozotocin (50 mg/kg i.p.). Daily doses of 400, 800, and 1000 mg/kg of extract were orally administered to fasted normal and diabetic rats. Blood glucose levels were monitored after 0, 2, 4, 8, 12 h and on day 14 post treatment. Liver glycogen levels were also estimated on day 14. In normal rats, only 400 mg/kg of the extract produced a significant reduction in blood glucose at the 4 h (P < 0.05) which was 22.15 ± 4.88%. In diabetic rats, the extract, 400, 800 mg/kg, caused significant reduction (P < 0.01), 51.87% ± 5.79% and 43.47% ± 8.06% respectively, with maximum effect at 8 h. This reduction in blood glucose was greater than that of glibenclamide (31.03% ± 8.86%). Diabetic rats administered with 400 mg/kg extract produced a significant reduction (P < 0.01) on day 14 (43.60% ± 8.10%). Liver glycogen levels were significantly increased (P < 0.05) in diabetic rats administered with doses of 400 and 800 mg/kg extracts and these were comparable to glibenclamide. Acute toxicity data showed no mortality in mice up to 17.5 g/kg. We conclude that the extract possesses marked hypoglycemic effects in diabetic rats possibly through increased glycogenesis, thus justifying its use in herbal medicine for the treatment of diabetes.

Studies on the anti-asthmatic and antitussive properties of aqueous leaf extract of Bryophyllum pinnatum in rodent species

OBJECTIVE To evaluate the antiasthmatic and antitussive properties of the aqueous leaf extract of Bryophyllum pinnatum (B. pinnatum) (BP) Lam. METHODS Ovalbumin-sensitized guinea pigs which were treated with BP for 21 consecutive days were exposed to 0.2% histamine aerosol in a glass chamber. Mucus viscosity, white blood cell and lymphocyte counts and tracheal wall morphometry were measured. Bouts of cough were counted pre and post acute exposure of extract-treated (× 7 d) guinea pigs to 7.5% citric acid aerosol in a chamber. Phenol red expectoration was estimated in mice after 7 d of daily administration of BP. RESULTS Doses of 200 and 400 mg/kg/day (×21 d) BP significantly increased the time for guinea pigs to experience preconvulsive dyspnoea. BP and salbutamol (0.5 mg/kg/day ×21 d) reduced mucus viscosity in the sensitized group to values comparable with controls. White blood cell, lymphocyte counts and tracheal morphometry were not significantly altered. Both doses of BP also significantly reduced the bouts of cough but only 400 mg/kg/day significantly inhibited the amount of phenol red secreted. CONCLUSIONS BP has demonstrated antiasthmatic and antitussive properties in these rodent models. These properties may underscore its use in Nigerian ethnomedicine.

Antiinflammatory Activity of Aqueous Extract of Stereospermum kunthianum (Cham, Sandrine Petit) Stem Bark in Rats.

Stereospermum kunthianum, Cham, Sandrine Petit (family: Bignoniaceae) is used in traditional medicine to treat bronchitis, pneumonia and coughs, gastritis, wounds, rheumatic arthritis, ulcers, dysentery, leprosy and venereal diseases in humans. The antiinflammatory activity of the aqueous extract of the stem bark was investigated with experimental animal models using the carrageenan-induced paw oedema, leucocytes migration and granuloma air pouch tests in rats. The extract (100, 200 or 400 mg/kg) at 3 h post-treatment caused a significant (p<0.05) reduction in the paw oedema in rats. The effect of the extract was most pronounced at the dose of 400 mg/kg and was higher than that of indomethacin (10 mg/kg). The extract (400 mg/kg) caused a significant (p<0.05) reduction in the number of recruited leucocytes and its inhibition of peritoneal exudate formation was comparable to that of indomethacin at a dose of 10 mg/kg. The exudate formation inhibited by 400 mg/kg of the extract in the granuloma air pouch test was comparatively less to that of indomethacin at a dose of 10 mg/kg. The findings of the study indicate that the aqueous extract of Stereospermum kunthianum stem bark possesses antiinflammatory activity which is probably related to the inhibition of prostaglandin synthesis. This is a possible rationale for its folkloric use as an antiinflammatory agent.

Evaluation of the protective and ameliorative properties of Garcinia kola on histamine-induced bronchoconstriction in guinea pigs.

Background: Garcinia kola is popularly used in African traditional medicine for the relief of acute bronchoconstrictive episodes. Objective: In this study, we examined the anti-asthmatic and morphological effects of the ethanol extract of G. kola in animal model. Materials and Methods: Guinea pigs were sensitized with ovalbumin and then given doses of 200 or 400 mg/kg/day for 21 consecutive days. Theophylline (10 mg/kg/day) was used as a standard. At the end of the exposure, the animals were exposed to 0.2% histamine aerosol in a chamber. Lymphocyte count, bronchial histology and morphometry were done. Results: Compared with non-sensitized controls, 200 mg/kg/day dose of the extract significantly (P < 0.05) increased the time taken for onset of preconvulsive dyspnea while the dose of 400 mg/kg/day significantly (P < 0.01) reduced bronchial wall thickness. Lymphocytes counts were not significantly affected but the bronchi of extract-treated animals were histologically clearer of lesions visible in the sensitized. Conclusion: These protective and ameliorative properties lend credence to the use of G. kola in ethnomedicine.

Effects of Leaf Extracts of Piliostigma thonningii Schum on Aortic Ring Contractility and Bleeding Time in Rats

The leaves of Piliostigma thonningii Schum have been used in herbal medicine to treat inflammations, bacterial infections, and worm infestations and to arrest bleeding. In an investigation of the possible scientific basis for the use of P. thonningii as a hemostatic agent, the contractility of isolated rat aortic rings and wound bleeding times were measured after exposure of the tissues to aqueous and ethanol extracts of P. thonningii leaves. The extracts produced responses on the isolated aortic rings. The maximum contractile response produced by 32 mg mL−1 of the aqueous extract was 30.8% ± 1.6% of the contractile response produced by 1 μM phenylephrine. The ethanol extract was much less potent with 64 mg mL−1 producing only 12.3% ± 0.9% of the contractile response produced with the phenylephrine. In addition, the aqueous extract, but not the ethanol extract, significantly reduced bleeding time as compared with saline solution (p < .05) but was significantly less than the reduction produced with 0.1% epinephrine solution. The constriction of blood vessels may be the basis for P. thonningiis use as a hemostatic agent in traditional herbal medicine.

Increased superoxide dismutase and Na+, K+-ATPase activities in aortic strips from potassium-adapted rats: implication for altered vascular reactivity

The contributions of superoxide dismutase (SOD) and Na(+), K(+)-ATPase to the altered vascular reactivity in potassium-adapted rats were investigated to test the hypothesis that smooth muscle hyperpolarisation may be involved. Isometric contractions to noradrenaline (NA), 5-hydroxytryptamine (5-HT), and relaxations to acetylcholine (ACh), levcromakalim (LEV) and sodium nitroprusside (SNP), were measured in aortic rings from potassium-adapted rats. Pieces of the aortae were also excised from the animals and assayed for SOD and Na(+), K(+)-ATPase. Maximum contractile responses were significantly attenuated (P<0.05) in aortic rings from the potassium-adapted rats to NA and 5-HT, while relaxations were also significantly augmented (P<0.05) in the same rings to LEV and SNP, but not to ACh. Both SOD and Na(+), K(+)-ATPase activities were significantly higher (P<0.05) in the aortae from the potassium-adapted rats compared to controls. It is concluded that the alteration in vascular smooth muscle reactivity may be due to hyperpolarisation caused by the activities of SOD and Na(+), K(+)-ATPase.

Haematological influences of potassium adaptation in normotensive and renally-hypertensive Wistar rats.

Abstract Dietary potassium is known to cause reduction in blood pressure in several models of hypertension in human and animal studies but its haematological effects are not known. Here, experiments are designed to study the haematological effects of potassium adaptation (achieved by administering 0.75% KCl solution in drinking water for five weeks) in Wistar rats. The animals are divided into four groups comprising controls, potassium-adapted, renal hypertensive, and renal hypertensive with later adaptation to potassium. Packed cell volume (PCV) and platelet count (PC), whole blood and plasma viscosities, and platelet aggregation in the presence of sodium nitroprusside, levcromakalim, and glibenclamide, are studied. Results showed comparable PCV and PC in all groups. While relative whole blood viscosity was significantly higher (P<0.05) in the hypertensive group, relative plasma viscosity was similar in all groups. Adaptation significantly reduced (P<0.05) the tendency of platelets to aggregate to collagen. Sodium nitroprusside significantly reduced (P<0.05) the pro-aggregatory effects of collagen only in the control group. Neither of the potassium-channel modulators (levcromakalim, glibenclamide) caused any significant alteration in platelet response to collagen at the concentrations studied. Although these results suggest that potassium adaptation may not affect haemorheology, the reduced ability of platelets to aggregate – by mechanisms not clearly understood – has implications for reduced thromboembolism and the attendant cardiovascular sequelae.

Evaluation of the anti-asthmatic and antitussive effects of concurrently administered extracts of Bryophyllum pinnatum and Andrographis paniculata in rodents

We evaluated the anti-asthmatic and antitussive effects of concurrently administered doses of aqueous Bryophyllum pinnatum (BP) and methanol Andrographis paniculata (AP) extracts in rodents. Doses of 200 and 400 mg/kg of BP were variously administered concurrently with 4 or 8 mg/kg of AP. In the anti-asthmatic evaluation, ovalbuminsensitized guinea pigs were given oral doses of both extracts for seven days and then exposed to 0.2% histamine aerosol in a glass chamber. Latency to preconvulsive dyspnea (PCD), tracheal fluid volume and viscosity were measured. In guinea pigs given acute doses of the extract, bouts of cough were counted after exposure to 7.5% citric acid aerosol. Phenol red expectoration was estimated in mice after 7 days of treatment with the extracts. Doses of BP administered alone significant increased latency to PCD (P < 0.05); and reduced the number of cough bouts (P < 0.0001). The concurrent administration of 400 mg/kg BP with the doses of AP significantly increased latency to PCD compared to 400 mg/kg BP alone. Doses of AP significantly altered the antitussive effect of BP but significantly reversed the reduction of phenol red release by 400 mg/kg BP. We conclude that while concurrent administration of 400 mg/kg BP with doses of AP may be beneficial in asthma, this is not the case in cough. This has implication on the label indications following possible co formulation of the extracts. Keywords: Concurrent extract administration, Asthma, cough, expectoration