Hot and Cold - and thyroid!

[helvella]

The simple version for us ordinary folk is here:

phys.org/news/2014-01-prote...

The actual paper (abstract, full paper and PDF) available here:

Temperature-responsive release of thyroxine and its environmental adaptation in Australians

Xiaoqiang Qi1,

Wee Lee Chan1,

Randy J. Read1,

Aiwu Zhou1,2 and

Robin W. Carrell1⇑

+ Author Affiliations

1Department of Haematology, Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, UK

2Key Laboratory of Cell Differentiation and Apoptosis of Ministry of Education of China, School of Medicine, Shanghai JiaoTong University, No. 280, Shanghai 200025, People's Republic of China

e-mail: [e-mail]

Abstract

The hormone thyroxine that regulates mammalian metabolism is carried and stored in the blood by thyroxine-binding globulin (TBG). We demonstrate here that the release of thyroxine from TBG occurs by a temperature-sensitive mechanism and show how this will provide a homoeostatic adjustment of the concentration of thyroxine to match metabolic needs, as with the hypothermia and torpor of small animals. In humans, a rise in temperature, as in infections, will trigger an accelerated release of thyroxine, resulting in a predictable 23% increase in the concentration of free thyroxine at 39°C. The in vivo relevance of this fever-response is affirmed in an environmental adaptation in aboriginal Australians. We show how two mutations incorporated in their TBG interact in a way that will halve the surge in thyroxine release, and hence the boost in metabolic rate that would otherwise occur as body temperatures exceed 37°C. The overall findings open insights into physiological changes that accompany variations in body temperature, as notably in fevers.

thyroxine

thyroxine-binding globulin

aboriginal Australian

febrile convulsions

hypothermia

hibernation

Received November 26, 2013.

Accepted January 7, 2014.

© 2014 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License creativecommons.org/license..., which permits unrestricted use, provided the original author and source are credited.

rspb.royalsocietypublishing...

And this related paper seems to be interesting for the impact of cold on T4 to T3 conversion:

Horm Metab Res. 2014 Jan 20. [Epub ahead of print]

Influence of Chronic Exposure to Cold Environment on Thyroid Gland Function in Rabbits.

Mustafa S1, Elgazzar A2.

Author information

1Department of Biomedical Sciences, College of Nursing, Public Authority for Applied Education & Training, Kuwait.

2Department of Nuclear Medicine, Faculty of Medicine, Kuwait University, Kuwait.

Abstract

Chronic exposure to cold can affect the thyroid gland. However, the effect on thyroid gland perfusion images and the ratio between thyroid hormones secretion were not addressed in any previous study. The present study investigates the effects of chronic cold exposure on thyroid gland function using radionuclide tracer and thyroid hormones secretion concentration. New Zealand white rabbits weighing approximately 1.8-2 kg were kept in a cold room (4°C) for 7 weeks. Thyroid scintigraphy was performed for cold exposed rabbits and a control rabbit group. Each rabbit was injected with 115 MBq (3.1 mCi) technetium-99m pertechnetate (99mTc pertechnetate). Studies were performed using Gamma camera equipped with a low energy, high resolution, pinhole collimator interfaced with a computer. Static images were acquired 20 min after administration of the radiotracer. Rabbits chronically exposed to cold had less body weights than control. Thyroid gland uptake is higher in rabbits chronically exposed to cold than controls using radionuclide perfusion study. The increase was proportional to the time period, so the increase after 7 weeks was greater than 5 weeks. There is also an increase in free triiodothyronine (FT3) and a decrease in free thyroxine (FT4) values. Our results indicate that thyroid gland uptake is higher in rabbits chronically exposed to cold than control and the increase was proportional to the duration. The decrease in rabbit body weights may be related to the increase in metabolism due to the increase of thyroid hormones. Chronic cold exposure also increased the conversion of T4 to T3, which is more potent in thermogenic effect.

© Georg Thieme Verlag KG Stuttgart · New York.

PMID: 24446160 [PubMed - as supplied by publisher]

ncbi.nlm.nih.gov/pubmed/244...

Rod

[PR4NOW]

Rod, fun stuff, wish the studies on CBG were open access. Dr. Barnes did a lot of work with rabbits, removing their thyroid and watching the results. The results, of course, were ones that we are all too familiar with. Kinda gives a different slant on the idea that a rabbits foot is lucky though. PR

[helvella Administrator Thyroid UK in reply to PR4NOW]

In my work, both now and on occasion for many years, I see people working in offices. The number who have 2 or 3 kW fan or convector heaters blasting them from September to May, or longer, is astonishing. All too often I actually feel unwell in that much heat.

The idea that our obsession with being warm could be having unwelcome effects doesn't seem too far fetched.

[PR4NOW in reply to helvella]

There was an interesting bit,"An enigmatic accompanying finding strengthens the deduction that the Ala191Thr mutation in aboriginal Australians is selectively advantageous. This is the presence of the linked second mutation, with the replacement of the leucine at 283 by a bulkier phenylalanine. The puzzle was that this Leu283Phe mutation occurs not uncommonly in other populations without any discernible functional consequences [26]." This makes me wonder in what populations the single mutation occurs and why only the aboriginals got the double mutation given the number of people that also live in hot climates.

I've also like being warm but I can't stand hot, dry air blasting me like you get out of a gas forced air furnace. I find the 60s and 70s F very comfortable but I certainly don't enjoy below 32F anymore. We've had way too much of that this winter. PR

[helvella Administrator Thyroid UK in reply to PR4NOW]

What is an F? <joke >

Yesterday morning at work it was 13 C in the office (55.4 F). I was perfectly comfortable - though in time I might have felt a bit cool. When I was at my lowest in terms of thyroid (highest TSH) I was far less able to tolerate relative coolth.

[PR4NOW in reply to helvella]

My thermometers read both F and C but after a lifetime thinking in F I still haven't adjusted to thinking in both. I'm lucky to remember that 32F = 0C, I think. At 55F I would be wearing some appropriate (warm) clothes. PR

[helvella Administrator Thyroid UK in reply to PR4NOW]

Live at -40 - then it doesn't matter which scale...

[Everdean]

Does this mean that we use more thyroid hormones in a cold environment, thus the need for more supplementation in these conditions?

Thanks

[helvella Administrator Thyroid UK in reply to Everdean]

I think that is quite possible. But the effect on typical modern humans in the UK who never really get cold, maybe the difference is quite small? (Having recently read a few translated Russian stories, they really DO get cold!)

(Of course, we hear of elderly folk getting hypothermic, but they are already compromised in many ways.)

Rod

[roslin]

In practice, should we take less T3 (and T4) when we have a fever?, I have had that advice before.

Roslin

[Jow11 in reply to roslin]

When I had a high fever, taking extra T3 lowered it. My dr found it astonishing.

[helvella Administrator Thyroid UK in reply to Jow11]

Very interesting.

I certainly don't know!!!

[sandi in reply to roslin]

Not sure about taking less but it might be the reason that many of us feel better when we have colds as has been remarked many times on here. Maybe if adequately medicated take less but maybe many of us are not actually adequately medicated hence feeling better with a raised temperature?

[Hidden in reply to sandi]

Yes - here's a really old post (not medicated)

healthunlocked.com/thyroidu...