In each tissue affected by diabetes, an early functional alteration occurs and heralds later structural dysfunction. In eye, peripheral nerve, and neo-vascular tissue, experimental diabetes, by activating the polyol pathway, results in an early defect in both the functional characteristics of these tissues and in a component of tissue inositol that is important in maintaining the activity of a rapidly-turning-over pool of phosphatidylinositol. This system has been shown to be crucial in maintaining a portion of the ouabain sensitive Na/K ATPase activity of the involved tissue. Inositol repletion and/or aldose reductase inhibition reverse the defect in inositol metabolism and in the functional abnormality in these tissues. Extensive preliminary data suggests that renal hemodynamics are also influenced by this abnormality in inositol metabolism since inositol supplementation or the use of the aldose reductase inhibitor sorbitol reverses the renal vasodilation of early experimental diabetes in the rat and thus normalizes the GFR. This early hemodynamic abnormality of vasodilation and glomerular hypertension and has been proposed to be a marker for and a pathogenetic mechanism of the later structural deterioration. Our proposal seeks to examine the mechanisms of this apparent beneficial action of inositol supplementation in experimental diabetes and to determine the potential long term benefits of this intervention on the structural and functional deterioration seen in the experimental animal with long term diabetes. Clearance and glomerular micropuncture measurements will be carried out in the rat to determine the effect of alterations in inositol metabolism on intrarenal hemodynamics including intraglomerular pressure and glomerular permeability. Glomerular mesangial cells (which have now been successfully grown in culture in our laboratory) will be studied in order to define the effects of alterations in inositol metabolism on various components of cellular metabolism in a defined tissue under rigorously controlled circumstances. Mesangial cell contractile response to agonists will be examined by measuring change in cell shape, in oxygen consumption, and in cell calcium. Cell phosphatidylinositol turnover will be studied by radiotracer pulse chase and by quantitative thin layer chromatographic and gas chromatographic techniques. Successful completion of these proposed experiments could provide a new understanding of the pathogenesis of the early functional changes which occur in clinical or experimental diabetes and a potential new therapeutic approach to the prevention of diabetic nephropathy.
