| dc.description.abstract | During the past years, several groups of natural
products have been shown to be effective poisons, whether
present in plants, micro-organisms or animal tissues.
Such natural poisons may represent various classes of
chemical structures, including alkaloids, saponins, cardiac
glycosides, amines, polynuclear hydrocarbons, polypeptides,
azoxyglycosides etc. On ingestion these toxins may
have varied effects which may depend on the concentration
level at which the toxin is ingested or on metabolic differences
among species. Consequently the compound can be
acutely toxic causing death within a few hours, most of
the known alkaloids, cardiac glycosides and bacterial
toxins fall into this group, or it may have varied effects
leading in due course to chronic illness and even death.
Certain hepato-toxins and carcinogens appertain to this
type. In Kenya there have been several reports on toxicity
by natural products, especially among livestock, but very
few toxins have been characterized. However, in special
circumstances, it has been possible to identify the plant
producing either severe toxicity or delayed chronic
diseases in a particular locality or in groups exposed
to an environmental factor.
The production of tumours of the liver, kidney and
lungs following chronic feeding of crude meal prepared
from the nuts of Encephalartos hildebrandtii was reported
by Mugera and Nderito (1968. E. hildebrandtii provides
a source of edible starch for the natives of Kenya of the
Coast Province during famine and whenever there is shortage
of food. It is also known to be eaten by livestock.
The water soluble hepato-toxin, rnacrozmnin, (methylazoxymethanol-S-prirneveroside,
CH3~ = N.CR
20. CSHgo4'C
6 o
HlOOS) has been isolated and characterized as the lethal
chem~cal from the seeds of E. hildebrandtii. Macrozamin
and its analogue cycasin, {methylazQxymethanol-B-glucoside
(CH3~ = N.CH20'C6HIlOS) which is found in the SL~as species o
is reported to be toxic and carcinogenic.
New impetus for further research on Cycads has been
the recognition of a possible relationship between the ingestion
of cycad material and the occurrence of a severe paralytic condition. According to Mason and v.7hiting .in-:
gestion of leaves of species of four of the genera are
reported to produce a neurological disorder in cattle,
involving the irreversible paralysis of the hind quarters.
A new etiological approach to thi~ neurological disorder
has been suggested by Vega and Bell who isolated a nonprotein
amino acid, a~amine-S-methylaminopropionic acid
(CH_-NH-CH -CH(NH )-COOH), from seeds of Cycas circinalis 3 2 2
(Cycadaceae) which they found neurotoxic in chickens during
preliminary investigations.
The distribution of azoxyglycosid~s in the Cycads
suggested a fair possibility of the presence of this unusual
amino-acid in the Cycads indigenous to Kenya, but it could
not be detected in either E. hildebrandtii or C. thuarsii.
The primary causes of mest cancers are still unknown,
however, the great activity and considerable diversity of
carc.inoqenici,ty shown by N-nitrose--compounds have led to
an increasing interest in them as possible environmental
hazards.
A chemical investigation of certain species of plants
from the valley of "Nasampola, Kenya, one or more of which
are thought to induce oesophageal and rumenal cancer in
cattle, was carried out for the presence of N-nitrosamines,
and secondary amines, which are implicated as possible
precursors of N-nitrosamines, in an attempt to account for
some epidemiological aspects of the o | en |
