فيزيولوجيا الحمل عند الناقة

موضوع: فيزيولوجيا الحمل عند الناقة 5/5/2011, 05:47

Maternal Recognition of Pregnancy

In all domestic farm animal
species, the developing conceptus must release a biochemical message to
the maternal organism that prevents the normal cyclical release of PGF2α
from the endometrium and thereby effectively prolongs the lifespan and
secretory functions of the CL.
This so-called maternal
recognition of pregnancy signal is secreted by trophoblast cells and in
ruminants it is known to be interferon tau (IFNτ).
Studies to date in pigs and
horses, both of which have a diffuse, non-invasive epitheliochorial
placenta, have indicated that interferon-like molecules of embryonic
origin are not secreted. However, the embryonic tissues of both these
species possess high aromatase activity and they can synthesize large
amounts of oestrogens in vitro from as early as day 10 after ovulation.
The camel is basically a
ruminant but it has an epithelial-chorial placenta like a horse and pig
and it is an induced ovulator in which the CL that develops after a
sterile mating has a lifespan of only 8 - 10 days. Hence, during normal
pregnancy the camel conceptus must pass its antiluteolytic signal to the
endometrium by day 8 or 9.
Until recently no one had
tried to indentify this maternal recognition pregnancy signal in
camelids, so we carried out some experiments to investigate the possible
roles of either foetal oestrogens or interferon-like proteins in this
process.
Results of incubation
experiments of known weights of embryonic tissues showed convincingly
that the young camel conceptus does not synthesize any interferon-like
proteins similar to ovine IFN.
In contrast however, further
incubation studies of embryonic tissue with tritiated (ie.
radioactively labelled with 3H) oestrogen precursors (i.e.
androstenedione) showed even more clearly that they produce strikingly
large amounts of both oestradiol -17β and oestrone from as early as day
10 after ovulation but concentrations of both oestradiol-17β and
oestrone declines from day 22 onwards and is neglible by day 60.
This onset of oestrogen
synthesizing ability by embryonic tissues coincides well with the
observed time of luteolysis following a sterile mating, thereby
prompting the suggestion that these foetal oestrogens may form an
important component of the vital maternal recognition of pregnancy
signal that must be transmitted by the embryo to maintain luteal
function

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