Mesangial uptake and processing of macromolecules in rats with diabetes mellitus.

The uptake and processing of colloidal carbon by the glomerular mesangium was studied in an attempt to determine whether abnormal mesangial function occurs in rats with longstanding streptozotocin-induced diabetes mellitus. The chronically diabetic rats were considerably smaller than their normal littermates receiving a similar dose of colloidal carbon based upon body weight. Thus, further control groups, animals weight-matched with the diabetic rats (younger rats) and littermates of the diabetic rats given the mean quantity of colloidal carbon administered to the diabetic rats, were included. Quantitative evaluation of renal tissues indicated that younger rats have more avid mesangial uptake of colloidal carbon from the circulation and more rapid processing of these macromolecules through the mesangium than the other groups studied. These quantitative studies did not demonstrate any marked impairment in diabetic rats in the over-all capacity of their mesangium to take up and process colloidal carbon when compared with the two groups of littermate nondiabetic animals. However, in those areas of the mesangium thickened by the diabetic process large aggregated of carbon accumulated and persisted over the 6-week period of the study. It appears, therefore, that those areas of the mesangium in diabetic rats with pathologic changes consequent to the diabetic state have significant functional impairment.