They live in the land down under: thyroid function and basal metabolic rate in the Blind Mole Rat, Spalax.

AbstractThe Israeli blind subterranean mole rat (Spalax ehrenbergi superspecies) lives in sealed underground burrows under extreme, hypoxic conditions. The four Israeli Spalax allospecies have adapted to different climates, the cool–humid (Spalax galili, 2 n = 52 chromosomes), semihumid (S. golani, 2 n = 54) north regions, warm–humid (S. carmeli, 2 n = 58) central region and the warm–dry S. judaei, 2 n = 60) southern regions. A dramatic interspecies decline in basal metabolic rate (BMR) from north to south, even after years of captivity, indicates a genetic basis for this BMR trait. We examined the possibility that the genetically-conditioned interspecies BMR difference was expressed via circulating thyroid hormone. An unexpected north to south increase in serum free thyroxine (FT4) and total 3, 5, 3′-triiodo-L-thyronine (T3) (p < 0.02) correlated negatively with previously published BMR measurements. The increases in serum FT4 and T3 were symmetrical, so that the T3:FT4 ratio – interpretable as an index ...