Increased distal nephron EGF content and altered distribution of peptide in compensatory renal hypertrophy

Epidermal growth factor (EGF) precursor is synthesized within kidney in the thick ascending limbs of Henle's loop and in distal tubule. Under baseline conditions EGF precursor is localized to the luminal membrane. In contrast, functional EGF receptors are present in basolateral membranes of sensitive renal cells. Immunostainable EGF is increased in contralateral kidneys following uninephrectomy of rats. To confirm this increase and determine whether the distribution of EGF changes in this setting, we measured immunostainable EGF in kidneys originating from rats 1, 2, 5, or 14 days following unilateral nephrectomy or sham surgery. There was a suggestion of an increase in immunostainable EGF in distal tubules 5 days postnephrectomy and a definite increase 14 days postnephrectomy. At 1 or 2 days postnephrectomy, and following sham surgery, immunostainable EGF was present predominantly at luminal membranes. In contrast, immunostainable EGF was present more diffusely throughout distal tubular cells at 5 and 14 days postnephrectomy and clearly localized adjacent to both luminal and antiluminal membranes in kidneys obtained 14 days postnephrectomy. EGF extractable from kidneys was increased significantly 5 and 14 days postnephrectomy. This material is the size of mature EGF. The altered localization of immunostainable peptide indicates that a redistribution of intracellular EGF accompanies increased synthesis postnephrectomy. Antiluminal EGF precursor or mature EGF present within kidney could act as a paracrine growth factor.