EFFECTS OF GROWTH-HORMONE ON RAT RENAL EPIDERMAL GROWTH-FACTOR EXPRESSION

The kidney is a site of synthesis for several polypeptide growth facto rs including epidermal growth factor (EGF) and insulin-like growth fac tor I (IGF-I). Interactions between growth hormone (GH) and growth fac tors have been described that regulate renal growth factor expression. For example, GH and EGF each enhances the expression of IGF-I in kidn ey. To further define interrelationships in this renal GH-growth facto r axis, we characterized the effect of GH on renal EGF expression in h ypophysectomized, pituitary-intact (normal) rats, and hypersomatotropi c rats. Levels of extractable immunoreactive mature EGF, levels of a 1 42-kDa EGF-precursor present in renal membrane fractions, and levels o f EGF mRNA were significantly reduced in kidneys from hypophysectomize d rats compared with levels in normal rats. Each was increased signifi cantly after the administration of GH to hypophysectomized rats. In co ntrast, induction of hypersomatotropism in normal rats by injection of GH for 17 days did not affect levels of extractable mature EGF or EGF mRNA measured in kidneys. We conclude that GH enhances the renal synt hesis of EGF in hypopituitary, but not in hypersomatotropic states.