生物活性/药理作用 | Levothyroxine (T4) is a synthetically
prepared levo isomer of thyroxine, the major hormone secreted from the
thyroid gland. Thyroxine is released from thyroglobulin by proteolysis and
secreted into the blood. Thyroxine is peripherally deiodinated to form
triiodothyronine (T3) which exerts a broad spectrum of stimulatory effects on
cell metabolism. Thyroid hormone increases the metabolic rate of cells of all
tissues in the body. In the fetus and newborn, thyroid hormone is important
for the growth and development of all tissues including bones and the brain.
In adults, thyroid hormone helps to maintain brain function, food metabolism,
and body temperature, among other effects. The symptoms of thyroid deficiency relieved by levothyroxine include slow speech, lack of energy, weight gain,
hair loss, dry thick skin and unusual sensitivity to cold. Levothyroxine is a synthetic levoisomer of
thyroxine (T4), similar to the endogenous hormone produced by the thyroid
gland. Thyroxine is de-iodinated to form triiodothyronine (T3) in the
peripheral tissues. T3 enters the cell and binds to nuclear thyroid hormone
receptors, and the hormone-receptor complex in turn triggers gene
and produces proteins required in the regulation of cellular respiration,
thermogenesis, cellular growth and differentiation, and metabolism of proteins, carbohydrates and lipids. T4 and T3 also possess cardiac stimulatory effect. |
