EXPRESSION OF THE INSULIN-LIKE-GROWTH-FACTOR SYSTEM IN THE HYPOKALEMIC RAT-KIDNEY

We studied the renal expression of the insulin-like growth factor (IGF ) system to gain a better perspective of its potential role in the hyp erplastic adaptation of the distal nephron to potassium deficiency. Ra ts were pair fed 1% or 0.002% potassium diets for periods up to 10 day s. IGF-I mRNA was diminished in potassium-deficient rats within 4 days , whereas mRNA for IGF binding protein-1 (IGFBP-1), a collecting duct- associated protein, was increased by day 7. At day 10 mRNA for IGFBP-1 in potassium-deficient animals averaged 2.07 +/- 0.53 (mean +/- SD, r elative densitometry units) compared with 0.89 +/- 0.26 in control rat s (n = 4, P = 0.002). Conversely, IGFBP-3, a binding protein chose mRN A has been localized to the interstitial compartment, averaged 2.40 +/ - 0.02 in potassium-deficient rats and 4.77 +/- 0.05 in controls (n = 4, P < 0.03) at day 10 of treatment. Immunohistochemistry performed us ing a specific IGFBP-1 antibody revealed hyperplasia of distal nephron segments along with an increase in IGFBP-1 in potassium-depleted rats . These data suggest that IGFBP-1 may play an important role in the co ntrol of cellular adaptations in the hypokalemic rat kidney either dir ectly by influencing cell migration or indirectly by localizing IGF-I to the distal nephron.