Effect of Diabetes on In Vivo Metabolism of [35S]-labeled Glomerular Basement Membrane

Glomerular basement membrane (GBM) was labeled in vivo by the injection of tracer amounts of [35S]-sulfate into normal and streptozotocin-diabetic rats. The biosynthesis and turnover of sulfated glycosaminoglycans in the GBM was determined from the specific activity of [35S] after pronase digestion of basement membranes purified from glomeruli isolated 1-7 days after injection. Peak radiolabeling of both normal and diabetic GBM occurred 24 h after injection and, when corrected for differences in serum sulfate specific activities, was less in diabetic than in normal samples. The specific activity of GBM sulfate, expressed as cpm/microgram uronic acid, progressively diminished over the ensuing period of study in both normal and diabetic samples. The rate of decrease in specific activity of [35S]-labeled GBM was not significantly different in diabetic preparations compared with that in normal controls. The findings are compatible with diminished sulfation and/or production but normal turnover of glycosaminoglycans in the renal GBM in experimental diabetes.