Reverse triiodothyronine, also known as rT
3, is an
isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...
of
triiodothyronine
Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.
Production of T3 and its prohormone thyroxi ...
(T
3).
Reverse T
3 is the third-most common iodothyronine the thyroid gland releases into the bloodstream, at 0.9%;
tetraiodothyronine (levothyroxine, T
4) constitutes 90% and T
3 is 9%. However, 95% of rT
3 in human blood is made elsewhere in the body, as
enzymes
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as pro ...
remove a particular
iodine
Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...
atom from T
4.
The production of hormone by the thyroid gland is controlled by the
hypothalamus
The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...
and
pituitary gland
The pituitary gland or hypophysis is an endocrine gland in vertebrates. In humans, the pituitary gland is located at the base of the human brain, brain, protruding off the bottom of the hypothalamus. The pituitary gland and the hypothalamus contr ...
. The physiological activity of thyroid hormone is regulated by a system of enzymes that activate, inactivate or simply discard the prohormone T
4 and in turn functionally modify T
3 and rT
3. These enzymes operate under complex direction of systems including neurotransmitters, hormones, markers of metabolism and immunological signals.
The levels of rT
3 increase in conditions such as
euthyroid sick syndrome because its clearance decreases while its production stays the same. The decreased clearance is possibly from lower
thyroxine 5-deiodinase activity in the peripheral tissue or decreased liver uptake of rT
3.
In addition, increased rT
3 concentrations result from upregulated
thyroxine 5-deiodinase activity in critical illness, starvation and fetal life.
Reactions
References
External links
*
{{Xenobiotic-sensing receptor modulators
Iodinated tyrosine derivatives
Thyroid