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

Among homeothermic animals, larger species generally have lower metabolic rates and live longer than do smaller species. Because Ames dwarf mice (dwarfs) 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 six normals during 24-h periods of ad lib feeding, 24-h food deprivation, anti 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 groups. 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 thermogenesis due to lack of those hormones. However, whether low T-co per se is related to the increased longevity of the dwarf mice remains an interesting possibility to be investigated. (C) 1999 Elsevier Science Inc.