Transplantation of insulin-like growth factor-ii-secreting tumors into nude rodents

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 ± 19 vs. /ml, rats; 159 ± 28 vs. 18 ± 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 ± 23 vs. 527 ± 67 ng/ml, rats; 300 ± 26 vs. 482 ± 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.