Re: thyroid hormone
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E.S.Prakash
Apr 6, 2011, 4:41:15 PM4/6/11
to khoo piggy, Medical Physiology at SOM, AIMST University
Khoo Wooi Choo:
Nice question and I take the liberty to post it to our Google Group so your colleagues may find this helpful.
The calorigenic effect of thyroid hormones is attributable to its effect on the Na-K ATPase. Thyroid hormones increases the activity of Na-K ATPase, and the increase in oxygen consumption it produces in tissues has been experimentally shown to be reduced in the presence of ouabain, an inhibitor of the Na-K ATPase. Also, some of the calorigenic effect of thyroid hormones is due to the fact that it mobilizes nonesterifed fatty acids (also called free fatty acids) from triacylglycerols in adipose tissue. Oxidation of fatty acids in turn in the liver and muscle generates ATP and some heat is generated as well. Your Point 2 below is correct - clinically, one of the manifestations of hypothyroidism is cold intolerance. This is because BMR is suppressed in hypothyroidism.
It is also important to note that thyroid hormones do not increase oxygen consumption in all metabolically active tissues (Ganong's Review of Medical Physiology, 2005, p. 324, Ch 18). Thyroid hormones do not increase O2 consumption in the adult brain, testes, uterus, lymph nodes, spleen and anterior pituitary. In the anterior pituitary at least, T4 actually decreases oxygen consumption - this is likely because it inhibits TSH secretion.
Hope this helps.
Prakash
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Nice question and I take the liberty to post it to our Google Group so your colleagues may find this helpful.
The calorigenic effect of thyroid hormones is attributable to its effect on the Na-K ATPase. Thyroid hormones increases the activity of Na-K ATPase, and the increase in oxygen consumption it produces in tissues has been experimentally shown to be reduced in the presence of ouabain, an inhibitor of the Na-K ATPase. Also, some of the calorigenic effect of thyroid hormones is due to the fact that it mobilizes nonesterifed fatty acids (also called free fatty acids) from triacylglycerols in adipose tissue. Oxidation of fatty acids in turn in the liver and muscle generates ATP and some heat is generated as well. Your Point 2 below is correct - clinically, one of the manifestations of hypothyroidism is cold intolerance. This is because BMR is suppressed in hypothyroidism.
It is also important to note that thyroid hormones do not increase oxygen consumption in all metabolically active tissues (Ganong's Review of Medical Physiology, 2005, p. 324, Ch 18). Thyroid hormones do not increase O2 consumption in the adult brain, testes, uterus, lymph nodes, spleen and anterior pituitary. In the anterior pituitary at least, T4 actually decreases oxygen consumption - this is likely because it inhibits TSH secretion.
Hope this helps.
Prakash
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On Tue, Apr 5, 2011 at 9:47 PM, khoo piggy <pigle...@gmail.com> wrote:
Dear Dr. PrakashI don't really understand what is meant by calorigenic action of T3 and T4. there are two explanations for this action from two different books.1. calorigenic effect is due to metabolism of fatty acid they mobilize.2. calorigenic action of TH represents a very significant fraction of the total heat produced everyday in a typical person.which one is the correct one? i am so blurred regarding this calorigenic action of TH.thx dr. for taking your time and clearing my doubts. heart it.BEST REGARDS!KHOO WOOI CHOO
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