dc.contributor.author |
Mendis, A. L. S. |
|
dc.date.accessioned |
2020-01-20T07:56:38Z |
|
dc.date.available |
2020-01-20T07:56:38Z |
|
dc.date.issued |
1990-03-30 |
|
dc.identifier.citation |
Mendis, A. L. S. (1990). PLACENTAL TRANSFER AND FETAL LOCALISATION OF THYROID HORMONES. London, Department of Molecular Endocrinology, University College and Middlesex School of Medicine, University of London, London. |
en_US |
dc.identifier.other |
38460 |
|
dc.identifier.uri |
http://ir.lib.ruh.ac.lk/xmlui/handle/iruor/59 |
|
dc.description.abstract |
Experimental studies were carried out on pregnant
rats using radiolabelled-thyroxine (125 I-thyroxine) to
determine whether thyroxine is taken up by placentae
and fetuses during pregnancy, particularly before the
onset of fetal thyroid gland function.
Gross uptake of 1.09 + 0.6 was seen from the 14th
day of gestation, and this increased throughout the
gestation period under investigation. A similar pattern
was observed in the fetal brain and liver. The
placentae had very high uptake rates of 22.1 + 5.7 at
day 14 which increased to 30.2 + 2.6 on the 20th day of
gestation. The placenta was observed to have an uptake
rate of over 5 times that of the maternal thyroid and
15-20 times that of other maternal organs.
Thyroxine uptake by individual tissues were
measured by using radiolabelled iodide (131 Iodide) as
an internal control to equate transcapillary * flow rates
(trans-membrane flux) of the iodide molecules. These
results showed a net uptake and utilisation (1.26 +
0.43) of thyroxine at day 14 (i.e. before the onset of
fetal thvroid function) but not afterwards (ps<l.O).
This indicated that maternal thyroxine is utilised by the fetus for its developmental requirements when the
fetal thyroid has not begun its own hormone secretion.
A study in vitro of 5 ’- monodeiodinase activity in
the placentae and fetuses was done to estimate the
metabolism of injected 125I-thyroxine in those tissues.
The fetuses had a high deiodination rate of 258 + 78.5
on day 14 and a sharp reduction to 62.8 + 17.4 on day
15. It reduced further thereafter. The deiodination
rates in the placentae were much higher, increasing
from 500.5 + 212.6 at day 13 to a peak of 964.2 + 439.9
on day 15. These results suggest a change in the
utilisation pattern of the injected 125 I-thyroxine.
High 5 ’- monodeiodination rates upto day 15 suggest
the placental transfer and fetal utilisation of active
hormone, whereas after onset of fetal thyroid gland
function on or about day 16, thyroxine is metabolised
by the placenta into inactive rT3 and molecular iodine.
These results indicate that maternal thyroxine has
an important role to play in fetal development before
the onset of fetal thyroid gland function, and also is
instrumental in the supply of iodine by its metabolism
in the placenta. This additional source of iodine, for
which the fetus does not have to compete with other
maternal orqans, may be of critical significance to
fetuses carried by mothers living in low-iodine environments. This has serious epidemiological
implications in the iodine-deficient regions of the
world where mental retardation and other less apparent
neurological deficits due to fetal deficiency of
thyroxine or iodine or both, are a grave threat to the
health and the quality of life of millions of people
who inhabit these regions. |
en_US |
dc.description.sponsorship |
This thesis is the outcome of research carried out
at the Department of Molecular Endocrinology, The
University College and Middlesex School of Medicine,
University of London, England during a two-year
fellowship (SC/202-3 SRL 8304) granted by the
International Atomic Energy Agency (IAEA). |
en_US |
dc.language.iso |
en |
en_US |
dc.publisher |
University of London |
en_US |
dc.relation.ispartofseries |
;38460 |
|
dc.subject |
thyroid |
en_US |
dc.subject |
hormones |
en_US |
dc.title |
PLACENTAL TRANSFER AND FETAL LOCALISATION OF THYROID HORMONES |
en_US |
dc.type |
PhD Thesis |
en_US |