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Life span extension by reduction in growth hormone-insulin-like growth factor-1 axis in a transgenic rat model
Isao Shimokawa1, Yoshikazu Higami, Masanori Utsuyama
1Department of Respiratory and Digestive Medicine, Division of Experimental Medicine, Pathology, and Gerontology, Nagasaki University School of Medicine, Nagasaki City, Japan. shimo@net.nagasaki-u.ac.jp
Abstract:
The longer life span in dwarf mice suggests that a reduction in the growth hormone (GH)-insulin-like growth factor (IGF)-1 axis retards aging and extends the life span in mammals. We tested this hypothesis in a transgenic strain of rats whose GH gene was suppressed by an anti-sense GH transgene. Male rats homozygous for the transgene (tg/tg) had a reduced number of pituitary GH cells, a lower plasma concentration of IGF-1, and a dwarf phenotype. Heterozygous rats (tg/-) had an intermediate phenotype in plasma IGF-1, food intake, and body weight between tg/tg and control (-/-) rats. The life span of tg/tg rats was 5 to 10% shorter than -/- rats. In contrast, the life span of tg/- rats was 7 to 10% longer than -/- rats. Pathological analysis suggested that neoplasms caused earlier death in tg/tg rats; in contrast, tg/- rats had reduced nonneoplastic diseases and a prolonged life span. Immunological analysis revealed a smaller population and lower activity of splenic natural killer cells in tg/tg rats. The results of the present study support the hypothesis, but suggest that there is an optimal level of the GH-IGF-1 axis to maximize survival in mammals.