Increased Kidney Metabolism as a Pathway to Kidney Tissue Hypoxia and Damage: Effects of Triiodothyronine and Dinitrophenol in Normoglycemic Rats

Abstract

Intrarenal tissue hypoxia is an acknowledged common pathway to end-stage renal disease in clinically common conditions associated with development of chronic kidney disease, such as diabetes and hypertension. In diabetic kidneys, increased oxygen metabolism mediated by mitochondrial uncoupling results in decreased kidney oxygen tension (PO₂) and contributes to the development of diabetic nephropathy. The present study investigated whether increased intrarenal oxygen metabolism per se can cause intrarenal tissue hypoxia and kidney damage, independently of confounding factors such as hyperglycemia and oxidative stress. Male Sprague–Dawley rats were untreated or treated with either triiodothyronine (T₃, 10 g/kg bw/day, subcutaneously for 10 days) or the mitochondria uncoupler dinitrophenol (DNP, 30 mg/kg bw/day, oral gavage for 14 days), after which in vivo kidney function was evaluated in terms of glomerular filtration rate (GFR, inulin clearance), renal blood flow (RBF, Transonic, PAH clearance), cortical PO₂ (Clark-type electrodes), kidney oxygen consumption (QO₂), and proteinuria. Administration of both T₃ and DNP increased kidney QO₂ and decreased PO₂ which resulted in proteinuria. However, GFR and RBF were unaltered by either treatment. The present study demonstrates that increased kidney metabolism per se can cause intrarenal tissue hypoxia which results in proteinuria. Increased kidney QO₂ and concomitantly reduced PO₂ may therefore be a mechanism for the development of chronic kidney disease and progression to end-stage renal disease.