The glomerular accumulation of basement membrane-like material (GBMM), mainly the result of exaggerated GBMM biosynthesis, is characteristic of human and experimental diabetes. Since net collagen formation may be modulated by the degree of glycosylation of newly formed collagen, a concomitantly enhanced bioavailability of uridine diphosphosugars (UDP-sugars) (coenzymes necessary for glycosyl transfer) could be an important determinant of exaggerated deposition of GBMM. We have previously demonstrated increased UDP- sugar bioavailability in isolated glomeruli df the diabetic rat. The objective of this study is to investigate the relationship between this alteration and enhanced GBMM formation. UDP-sugar bioavailability can be predictably modified as shown by us in recent work involving uracil ribonucleotide metabolism in isolated glomeruli and in glomerular epithelial and mesangial cells in tissue culture. UDP-sugarbioavailability will be limited or enhanced by variations in exogenous precursor concentration. This will include studies in rats fed high and low protein diets since we have shown that protein intake influences the plasma concentration of uridine and orotate. Uracil ribonucleotide biosynthesis will be limited utilizing competitive inhibitors and by the administration of purified uridine phosphorylase. GBMM synthesis and breakdown during variation of uracil ribonucleotide metabolism will be studied in isolated glomeruli, primary cultures of mesangial cells and in cultures of a cloned mesangial cell line (high producer of GBMM) according to the incorporation of radiola- beled precursors. Studies will be carried out also in animals with long term diabetes in which glomerular function will be related to GBMM accumulation assessed by morphometric techniques. Nucleotides and amino acids will be measured by HPLC analysis and sugar composition of GBMM components by gas chromatographic analysis according to methods already established in our laboratory. The studies proposed should provide new information on the pathogenesis of diabetic renal disease and its relationship to protein intake.
