Early life growth hormone treatment shortens longevity and decreases cellular stress resistance in long-lived mutant mice.

Hypopituitary Ames dwarf mice were injected either with growth hormone (GH) or thyroxine for a 6-wk period to see whether this intervention would reverse their long life span or the resistance of their cells to lethal stresses. Ames dwarf mice survived 987 ± 24 d (median), longer than nonmutant control mice (664 ± 48), but GH-injected dwarf mice did not differ from controls (707 ± 9). Fibroblast cells from Ames dwarf mice were more resistant to cadmium than cells from nonmutant controls (LD(50) values of 9.98 ± 1.7 and 3.9 ± 0.8, respectively), but GH injections into Ames dwarf mice restored the normal level of cadmium resistance (LD(50)=5.8 ± 0.9). Similar restoration of normal resistance was observed for fibroblasts exposed to paraquat, methyl methanesulfonate, and rotenone (P<0.05 in each case for contrast of GH-treated vs. untreated dwarf mice; P<0.05 for dwarf vs. nonmutant control mice.) T4 injections into Ames dwarf mice, in contrast, did not restore normal life span. We conclude that the remarkable life-span extension of Ames dwarf mice, and the stress resistance of cells from these mice, depends on low levels of GH exposure in juvenile and very young adult mice.