Interaction between hypersomatotropism and age in the Wistar-Furth rat

The purpose of this study was to examine body growth parameters and serum somatomedin levels in progressively older rats exposed to high levels of circulating growth hormone (GH). The effects of growth hormone secreting tumors arising from GH₃ cell injection were evaluated in 3, 5, 9, 18 and 24 month old female Wistar-Furth rats. In all tumor-bearing rat age groups, body weights were in excess of 70% of age-matched controls. Contributing to these body weight gains were significant increases in heart, liver, kidney and hind limb muscle weights. Fat pads from the tumored groups were similar to controls in the young (3, 5, 9 month) rats but were significantly smaller in the older groups at 18 and 24 months. Elevated GH predictably increased somatomedin levels in young rats while in the 18 and 24 month old groups, smaller increases were noted. These results show that old rats respond to GH in a mechanism involving somatomedin and that significant increases in somatic growth can be obtained, even at advanced age.