Dual regulation of insulin-like growth factor I expression during renal hypertrophy

We examined the regulation of insulin-like growth factor I (IGF-I) in kidney during the renal hypertrophy produced by two different experimental models: growth hormone treatment of hypophysectomized rats and compensatory hypertrophy subsequent to unilateral nephrectomy. Immunostaining for IGF-I in collecting ducts was enhanced in kidneys from growth hormone-repleted hypophysectomized rats, and the levels of IGF-I mRNAs were increased. In compensatory hypertrophy, no enhancement of the intensity of immunostaining was observed in kidneys of nephrectomized rats until 5 days postnephrectomy, at which time immunostainable IGF-I was increased markedly in medullary collecting ducts of hypertrophied kidneys compared with kidneys from sham-operated animals. No difference in steady-state levels of any IGF-I mRNA species was detected in whole kidneys or in collecting ducts from nephrectomized or sham-operated rats at any time postnephrectomy. Our findings demonstrate an increase in both IGF-I mRNA and in immunostainable IGF-I in collecting duct in the setting of growth hormone-induced renal hypertrophy but suggest that other, possibly translational, mechanisms underlie the induction of IGF-I synthesis during compensatory hypertrophy.