Introduction: Retinoic Acid (RA) are compounds derived from retinol or vitamin A. RA
signaling has a central role during both embryonic and adult growth, activating gene
transcription via interacting with nuclear RA receptors bound to RA response elements near
target genes. RA levels require precise regulation by controlled synthesis and catabolism. Citral
is a natural product of the essential oils of plants. It has been reported to inhibit the formation of
RA. Aim of the work: This research aims to find out which concentration 0.25, 0.5 or 1 µgm of
retinoic acid is most efficient in rescuing the chick embryo treated with citral. Methods:
Fertilized eggs of the chick Gallus domesticus were divided into six groups, control group, DMSO
group (RA solvent), citral group (50 µM) and three groups received a combination of the citral
dose and one of three different doses of RA (0.25, 0.5 or 1 µgm), respectively. After hatching,
hatchability and mortality rates were reported. Embryos were morphologically examined and
weighed. Morphometric measurements were carried out for some parameters and were
statistically analyzed. Results: the present study showed highly deformed embryos in the citral
group, while co-treatment with citral and the lowest dose of RA (0.25 µgm) showed partial
mitigation than the higher doses (0.5 and 1 µgm). Co-treatments of citral and RA (0.25, 0.5 and 1
µgm) showed mortality rates 40%, 74% and 75% respectively compared to 62.5% in the case of
citral treatment alone. Different abnormalities were observed in citral treated embryos such as
high growth retardation, brain deformation. The eye was either invaginated, exophthalmic or
completely absent in some embryos. Long and wry neck, absence of feathers, open body cavity
and limb deformation were also observed. Weight, crown rump, head length, head
circumference, head height, wing and all parts of hind limb lengths in all treated groups were
significantly lower than control. Also, co-treatment with the lowest dose of RA (0.25 µgm) and
citral significantly elevated the all morphometric parameters compared to higher doses of RA
(0.5 and 1 µgm), but non- significantly compared to citral treated group alone. Conclusion: This
study shows that treatment with citral decreases the level of endogenous RA than the level
needed to maintain the normal embryonic development and that leads to severe malformation.
Treatment with exogenous RA might rescue the embryo from teratogenic effects of citral and
that leads to the partial mitigation in some embryos. It suggested that the response of embryos to
RA is very sensitive. The lowest dose of RA (0.25 µgm) could partially mitigate the effect of citral
while higher doses of RA (0.5 and 1 µgm) exerted teratogenic properties of RA rather than
mitigative effects.