GH1 and hypothyroidism: Ames and Snell dwarfs, which represent some of the extremes of mouse longevity, are both GH- and thyroid stimulating hormone-deficient and, thus, profoundly hypothyroid.18,19 Chronic thyroxine treatment can shorten longevity of Snell dwarf mice,95 as well as normal rats 96 while subclinical hypothyroidism was associated with exceptional longevity in women.97,98 However, treatment of dwarf mice with thyroxine limited to the peripubertal period did not alter their longevity.93,99