Antiplasmodial Potential of the African Mistletoe: Agelanthus dodoneifolius Polh and Wiens.

Preparations of Agelanthus dodoneifolius have been used in the traditional Nigerian medicine to treat malaria and this practice has remained till date without scientific validation. The antiplasmodial property of the water extract of Agelanthus dodoneifolius was evaluated in vivo and in vitro against Plasmodium berghei and clinical isolates of Plasmodium falciparum, respectively. There was a dose-dependent inhibition of parasitaemia in the in vivo antiplasmodial tests likewise, the in vitro screening demonstrated a strong and concentration-dependent activity (21.54 µg/ml < IC(50) < 50 µg/ml) of the extract against the clinical isolates of Plasmodium falciparum. The phytochemical analysis revealed the presence of tannins, saponins, sterols, glycosides, phenols, anthraquinones, terpenes, reducing sugars and resins. It also showed a strong free-radical scavenging activity on 2, 2-diphenyl-2-picrylhydrazyl. The oral median lethal dose (LD(50)) in mice was estimated to be greater than 5000 mg/kg. Our results evidence that Agelanthus dodoneifolius may contain biologically active principles those are relevant in the treatment of malaria, thus supporting further studies of its active components.

Phytochemical and pharmacological studies on Monechma ciliatum.

The leaves of Monechma ciliatum were found to contain alkaloids, glycosides, proteins, tannins and saponins. The hot methanol extract (HME) of the leaves, previously found to have potent oxytocic effect in various species was fractionated in various solvents and the fractions analysed chemically and also assayed on the rat uterus in an attempt to identify the chemical constituents present and in particular the oxytocic principle. Positive reaction with ninhydrin spray suggests that the oxytocic constituent is an amino acidic derivative.

Bioassay-directed isolation of oxytocic principles from the methanol extract of Monechma ciliatum.

The hot methanol extract (HME) of Monechma ciliatum which has been reported to have potent oxytocic activity was purified by fractionation in an attempt to isolate the oxytocic principle. Thin layer analysis indicated that the oxytocic fraction was very polar. A positive reaction with ninhydrin-spray suggested that it is an amino acid/protein. Repeated column chromatography (CC) on silica gel followed by sephadex LH-20 column, accompanied by bioassay of the fractions on the rat isolated uterus enabled partial isolation of the oxytocic principle (P3) to be achieved. Although the exact structure of P3 could not be identified from the present study, various spectral analyses suggest that it is a small peptide made up of tyrosine, leucine and a third component which is probably serine. It is interesting to note that the parent compound, oxytocin, is also a peptide with tyrosine and leucine in its structure.

Uterotonic properties of the methanol extract of Monechma ciliatum.

The oxytocic activity of the hot methanol extract (HME) of the leaves of Monechma ciliatum was compared with other uterine stimulants like ergometrine, oxytocin, 5-hydroxytryptamine (5-HT), acetylcholine (ACh) and prostaglandins (PGs) E2 and F2alpha (PGE2 and PGF2alpha) in the presence of some antagonists in an attempt to explain the mechanism of action of the extract. The effects of the reference drugs on uteri isolated from rats pretreated with HME for 2 weeks were also observed. Atropine blocked the effect of ACh and partially blocked those of HME while L-366-948 blocked only the effect of oxytocin. Indomethacin inhibited the effects of HME as well as all the other drugs, except the PGs and ACh. D-600 blocked the effect of all the drugs including HME. Methysergide antagonised only the effect of 5-HT and partially blocked ergometrine. Prolonged treatment altered the uterine musculature and the activity profile of the reference drugs. These results suggest that the HME may be acting by more than one mechanism to contract the uterus and explains the mechanism of the anti-implantation activity of the plant.

Anticonceptive and estrogenic effects of a seed extract of Ricinus communis var. minor.

An ether-soluble fraction of a methanol extract of Ricinus communis var. minor seeds administered subcutaneously to adult female rats and rabbits at doses up to 1.2 g/kg and 600 mg/kg, respectively, in divided doses showed anti-implantation and anticonceptive activities. Laparotomy performed on Day 10 and Day 15 of pregnancy on mated female rats and rabbits treated with the extract did not reveal any uterine implantation sites. The animals were protected against pregnancy for over three gestation periods and among those that later delivered, there was no evidence of abnormality in the pups. In ovariectomized young female rats as well as in immature mice, the extract dose-dependently increased uterine wet weight. Furthermore, the extract induced premature opening of the vagina, increased the number of epithelial cells and cornified cells and decreased the leucocyte number in the vaginal smear. The estrogen-like activities exhibited by the extract were dose-dependent and the anticonceptive effect may be due at least in part to such estrogenic action.

Mechanisms of the relaxations induced by 5-hydroxytryptamine on the rat isolated caecum.

The mechanism by which 5-HT produces relaxations of the rat caecum has been examined. Propranolol and cocaine markedly attenuated the relaxations whereas tetrodotoxin had no effect. Higher doses of propranolol and cocaine (greater than 10(-6) M), as well as reserpinization, converted the relaxations into contractions. There was a residual relaxation resistant to propranolol, cocaine and reserpine treatment. High doses of 5-HT (greater than 10(-5) M) were thus thought to relax the rat caecum indirectly, through the release of noradrenaline from the tissue by a tyramine-like action. The relaxations do not seem to be due only to the release of noradrenaline.