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younger leaves (
). Ecdysteroids differ markedly
from vertebrate steroid hormones in their polarity (poly-
hydroxylated), bulk (C
27
­C
29
) and shape (A/B-cis-ring
junction), thus one would expect there to be little interaction
with the steroid-hormone receptors or steroid-metabolising
enzymes in mammals. Unfortunately, this has not been
systematically verified. The mechanisms, by which any
pharmacological effects of ecdysteroids in mammals are
mediated, are presently unknown (but see below).
Metabolism of ecdysteroids in mammals
Injected or ingested ecdysteroids are rapidly cleared from the
blood. In mice, ecdysone (
) undergoes a complex array
of metabolic reactions, including dehydroxylation (removal of
the 14a-OH) most probably by gut bacteria (cf. dehydrox-
ylation of bile acids), reduction in the B-ring and
epimerisation at C-3 (
). In addition, when
a 20,22-diol is present (as in 20E), side-chain cleavage can
take place between C-20 and C-22 and the pattern of
metabolites becomes very complex (Kumpun, Girault, Blais,
Maria, Dauphin-Villemant, Yingyongnarongkul, Suksamrarn
and Lafont, unpublished data). 14-Dehydroxylation also takes
place in humans (
). Methods aimed at analysing
20E and its metabolites in human urine are presently being
developed as anti-doping controls for humans and cattle
(
).
Pharmacological effects of ecdysteroids on
mammals
Pharmacological tests were first performed on mammals
(mice, rats) in the late 1960s to detect any harmful effects of
ecdysteroids on vertebrate organisms, which could have
precluded their use as insecticides. This was the starting point
for many experiments, which reported a wide array of
pharmacological effects of ecdysteroids on mammals (
,
,
).
Early pharmacological experiments
First of all, it must be emphasised that the acute toxicity of
ecdysteroids in mammals is very low: the LD
50
for 20E is
above 6 g/kg. The first reported effect of ecdysteroids on
mammals was a stimulation of protein synthesis (translation)
in vitro by liver polysomes prepared from rats having received
20E (or any of the other then available ecdysteroids). This
effect was even used as a convenient bioassay for the presence
of phytoecdysteroids in plant extracts during large-scale
screening programmes (
). At the same time,
other authors analysed the distribution and metabolic fate of
injected [
3
H]ecdysone (
These pioneering studies were followed by extensive
studies on possible anabolic effects of ecdysteroids in rats
(and humans). The general strategy was to compare the
physical performance or biochemical parameters of animals
having received 20E (or another ecdysteroid) over 1­3 weeks
to controls or animals treated with a `classical' anabolic steroid
(testosterone or dianabol), and these experiments indicated a
significant anabolic effect of ecdysteroids. Several ecdysteroid
preparations have been designed for sportsmen (e.g.
`Ekdisten' or `Retibol') containing quite small amounts of
20E (5 mg/tablet). Since those early times, the market for
ecdysteroid-containing preparations has developed consider-
ably, and is now especially aimed at bodybuilders; presently,
ca. 300 ecdysteroid-containing products are available on the
market, some of which contain large amounts of 20E, with
formulations recommending up to 1 g daily intake, usually in
combination with other known anabolic chemicals and/or
Figure 1 The structure of 20-hydroxyecdysone.
L DINAN
and
R LAFONT
$
Ecdysteroid effects and applications
2
Journal of Endocrinology (2006) 191, 1­8
www.endocrinology-journals.org

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