Low body temperature in long-lived Ames dwarf mice at rest and during stress

Among homeothermic animals, larger species generally have lower metabolic r ates and live longer than do smaller species. Because Ames dwarf mice (dwar fs) live approximately 1 year longer than their larger normal sex- and age- matched siblings (normals), we hypothesized that they would have lower body core temperature (T-co). We, therefore, measured T-co of six dwarfs and si x normals during 24-h periods of ad lib feeding, 24-h food deprivation, ant i emotional stress induced by cage switching. With ad lib feeding, T-co of dwarfs averaged 1.6 degrees C lower than normals; during food deprivation, T-co of both dwarfs and controls was significantly lower than when food was available ad lib; and following cage switch, T-co was elevated in both gro ups. However, during all three experiments, T-co was significantly lower in dwarfs than in normals. These data support the hypothesis that Ames dwarf mice, which live longer than normal size controls, maintain lower T-co than normals. Because dwarfs are deficient in thyroid stimulating hormone (TSH) and growth hormone (GH), their low T-co may be a result of reduced thermog enesis due to lack of those hormones. However, whether low T-co per se is r elated to the increased longevity of the dwarf mice remains an interesting possibility to be investigated. (C) 1999 Elsevier Science Inc.