Vol. 280, Issue 1, R149-R155, January 2001
Cold-induced changes in thyroid function in a poikilothermic
mammal, the naked mole-rat
Rochelle
Buffenstein1,2,
Ryan
Woodley1,
Cleopatra
Thomadakis1,
T. Joseph M.
Daly1, and
David A.
Gray3
Departments of 1 Anatomical Sciences and
3 Physiology, Medical School of the University of the
Witwatersrand, Park Town, South Africa 2193; and 2 Department of
Biology, City College of City University of New York, New York, New
York 10031
Cold acclimation induces very
divergent responses in thyroid function in reptiles and mammals
reflective of their different thermoregulatory modes. Naked mole-rats,
unlike other small mammals, are unable to effectively employ endothermy
and are operatively poikilotherms. We therefore
investigated changes in their thyroid status with chronic cold
exposure. Under simulated burrow conditions, free thyroxine
(T4; 0.39 ± 0.09 ng/dl) and thyroid stimulating hormone (TSH; 1.12 ± 0.56 µIU/ml) levels fell within the
reptilian range, one order of magnitude lower than mammalian levels.
However, cold induced typical mammalian responses: free T4
levels (0.55 ± 0.09 ng/dl) and thyroid follicular cell height
were significantly greater. Although TSH levels (1.28 ± 0.83 µIU/ml) were not significantly elevated, thyrotrophs exhibited
ultrastructural signs of increased secretory activity. Low thyroid
hormone concentrations may contribute substantially to the unusual
thermoregulatory mode exhibited by naked mole-rats.
follicular cell height; thyroxine; thyrotrophs; thyroid-stimulating
hormone
