Restricted supplies of insulin-like growth factor II (IGF-II) have severely limited investigations of the in vivo actions of this hormone. To circumvent this problem, we have developed an in vivo rodent model in which rat (r) IGF-IIsecreting cells (18, 54-SF) are transplanted into congenitally immunodeficient (nude) rats and mice. These cells proliferate and form discrete tumors that contain rIGF-II and abundant IGF-II receptors. The tumors also secrete rIGF-II into the circulation, resulting in plasma rIGF-II concentrations many-fold greater than those in control rodents (81 Â± 19 vs. /ml, rats; 159 Â± 28 vs. 18 Â± 5 ng/ml, mice; P.0.05, both groups). There was no significant difference between the tumor-bearing and control rodents in either body weight, or tail length. The tumor-bearing rodents did have significantly lower concentrations of IGF-I (296 Â± 23 vs. 527 Â± 67 ng/ml, rats; 300 Â± 26 vs. 482 Â± 70 ng/ml, mice; P < 0.05, both groups), suggesting that the increased concentrations of rlGF-II may have inhibited IGFI production or secretion. This animal model may be used to explore the biological effects of increased plasma IGF-II concentrations.
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