Renal cellular biology of growth hormone and insulin-like growth factor I.

Growth hormone (GH) and insulin-like growth factor I (IGF-I) exert a variety of actions in renal tissue. To shed light upon the renal GH-IGF I axis we have characterized the cell biology of GH and IGF I in two parts of the nephron that are targets for these peptides, proximal tubule and collecting duct. Receptors for both GH and IGF I are present in the basolateral membrane of the renal proximal tubular cell. GH activates phospholipase C and IGF I stimulates phosphorylation of its receptor at this site. Both peptides directly enhance gluconeogenesis in proximal tubule. GH stimulates IGF I gene expression in collecting duct. IGF I of collecting duct origin could act as a paracrine growth factor in other portions of the nephron. IGF I may be causative of renal hypertrophy that occurs in the settings of hypersomatotropism, unilateral nephrectomy (compensatory hypertrophy) and diabetes mellitus.