Relationship between renal function and metabolic alterations in early streptozocin-induced diabetes in rats

To investigate the temporal relationship of diabetes-induced renal growth and its associated metabolic alterations to the early development of renal hyperfunction, parallel functional and metabolic studies were performed shortly after the onset of diabetes in rats. Hyperglycemia and hypoinsulinemia were evident 18 h after streptozocin injection, and significant hyperglucagonemia and acidosis were present at 36-48 h. Glomerular filtration rate (GFR), expressed per unit of body weight, first increased at 3 days of diabetes [1.35 +/- 0.07 (SE) (N = 14)] and was 18% greater than in controls [1.14 +/- 0.03 ml X min-1 X 100 g-1 (SE) (N = 38)] (P less than .005). Renal enlargement preceded GFR changes, so that GFR per unit of kidney weight was lower at 48 h in diabetics [1.31 +/- 0.06 (SE) (N = 16)] than in controls [1.54 +/- 0.04 ml X min-1 X g-1 (SE) (N = 38)] (P less than .01). Nucleotide and RNA metabolism was studied in the renal cortex after infusion of radio-labeled orotate or adenine. Rate of RNA synthesis, total cellular RNA, and the pools of ATP, UTP, and uridine 5'-diphospho-N-acetyl glucosamine were significantly increased 13-51% in 48-h diabetics. Nucleotide precursor incorporation was significantly increased only in uracil ribonucleotides. The increase in uracil ribonucleotide pool exceeded the degree of cell hypertrophy. Our studies indicate that renal hypertrophy and specific increases in uracil ribonucleotide synthesis precede functional changes in early diabetes. Renal metabolic changes may be the critical primary factors in diabetic nephropathy.