Regulation of renal growth and IGFBP-4 expression by triiodothyronine during rat development

The insulin-like growth factors (IGFs) and insulin-like growth factor bindi ng proteins (IGFBPs), which regulate ICF activity, play a fundamental role in renal cell proliferation and differentiation. The thyroid hormone is con sidered to be required for kidney development; excess induces local hypertr ophy and hyperplasia. The aim of the present study was to investigate the p ossible involvement of the IGF/IGFBP system in thyroid hormone-induced rena l growth during the development of the rat. Our results show that thyroid h ormone withdrawal by 6-propyl-2-thiouracil (PTU)-treatment of rats at all a ges had no effect on renal IGFBP-4 mRNA levels, whereas the abundance of th e serum protein was decreased compared to controls. Intraperitoneal triiodo thyronine (T-3) administration to hypothyroid rats resulted in renal hypert rophy associated with a significant upregulation of IGFBP-4 expression with increased levels of renal IGFBP-4 mRNA and serum protein. T-3-induced upre gulation of IGFBP-4 expression suggests the involvement of the local IGF/IG FBP system in T-3-induced renal hypertrophy.