Agriculture Reference
In-Depth Information
Description —
The plant is 12-30 m in height and about 0.6-1 m in girth. It has a grayish bark;
the slash is yellowish with dark flecks and fibrous, yielding rather scanty latex with other blackish
branchlets. The leaves are oblong-lanceolate to broadly oblong-elliptic, shortly acuminate, with the
blade rounded to slightly cunneate. They are dark green, leathery, and glossy glabrous. There are
numerous parallel nerves, rather faint, with thinner veins between. It produces white flowers, up to 5
cm wide, borne in terminal inflorescence. The entire inflorescence is glabrous; the calyx is about 2.5
cm long, broadly cup shaped at the base with 5 overlapped triangular-ovate lobes. The corolla tube is
slender, about 2.5 cm long, showing 5 elliptic corolla lobes.
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The fruits occur usually in pairs, hang-
ing at the end of a long stalk. They are broadly ovoid, smooth, glabrous, and leaf green in color, turn-
ing to yellow or orange when ripe. They vary enormously in size, up to 15 cm long and 10 cm wide and
contain numerous seeds (5-10 cm wide) embedded in a pulp. All parts of the plant are very bitter.
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Habitat and Distribution —
Picralima
occurs in deciduous forests and is widely distributed in
tropical Africa, although sparse. It has been located in Ghana, Ivory Coast, Angola, Nigeria, Zaire,
Cameroon, and Tanzania.
Ethnomedicinal Uses —
Extracts of the leaves, seeds, or stem bark are used in the preparation
of various fever and malaria remedies. In Central Africa, it is used for the treatment of primary
hypertension, malaria, and jaundice.
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The crushed seeds are eaten for stomachache and pneumo-
nia. Extracts of the stem bark and seeds are administered for venereal diseases and as a vermifuge.
In herbal markets in Ghana, Nigeria, and Ivory Coast, Akuamma seeds, the stem bark, and dried
fruit rind are highly prized as antimalarial agents and a remedy for sleeping sickness. The seeds are
used in the preparation of a treatment for insanity and related CNS diseases. The root decoction is
dispensed as a cure for yellow fever.
Constituents —
The plant elaborates a complex mixture of indole and dihyroindole alkaloids,
including alstonine, akuammiline, akuammidine, akuammine, Ψ-akuammigine, akuammicine,
echitamine, picraline, picratidine, and picraphylline.
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Pharmacological Studies —
Extracts of the plant have been shown to possess local anesthetic,
opiate receptor, antihypertensive, and sympatholytic properties. The plant contains several indole
alkaloids, of which the major ones include akuammidine, akuammine, and Ψ-akuammigine. The
leaves elaborate picraphylline and picraline, among several other indole bases. Akuammidine has a
sympatholytic action and a hypotensive effect, which was reported to be weaker than that of yohim-
bine.
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The compound also showed strong local anesthetic action, which was found to be three
times that of cocaine hydrochloride.
858,859
The aqueous decoction of the bark has been shown to be
active against
Trypanosoma brucei
.
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The major alkaloids of the fruits of
P. nitida
have been examined for
in vitro
activity against
drug-resistant and -sensitive strains of
Plasmodium falciparum.
The alkaloids showed remarkable
inhibitory activity against both clones of
P. falciparum
at IC
50
values of 0.08-0.9 µg/ml. Among the
compounds tested, those belonging to the picraline-akuammine subgroup showed greatest activity,
followed by those of the akuammicine type. The alkaloid echitamine was inactive.
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The alkaloids
also demonstrated strong inhibitory activity against clinical isolates of
Leishmania
and trypanosomes.
Although the mechanism of action of
Picralima
is yet to be determined, the drug is presently
used as a crude extract in traditional African medicine as an antimalarial and for the control of
blood pressure. Alstonine, found in the seeds and fruit rind, has shown antipsychotic-like effects,
a putative antipsychotic, which consistently differed from the effects of known drugs in various
mouse models.
862,863
Treatment with alstonine was able to prevent MK801-induced working memory
deficit, indicating its potential benefit for cognitive deficits now seen as a core symptom in the dis-
ease. Corroborating previously reported data, alstonine was also effective in counteracting MK801-
induced hyperlocomotion and social interaction deficit. Ritanserin, a 5-HT
2A/C
receptor antagonist,
prevented alstonine's effects on these three behavioral parameters. Available evidence suggests that
5-HT
2A/C
receptors are central to the antipsychotic-like effects of alstonine, consistently seen in
mouse models relevant to the three dimensions of schizophrenia symptoms.
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