Phenotypic expression of collagen types in mesangial matrix of diabetic and nondiabetic rats.

This study was performed to evaluate the composition of the extracellular matrix of the mesangium in both diabetic and nondiabetic rats. Four groups of rats (n = 10 each) were studied. Nondiabetic rats were injected with saline (group 1) or insulin (3.5 U NPH daily) (group 2). Streptozocin-induced diabetic rats were similarly injected with saline (group 3) or insulin (group 4). Six weeks after initiation of study, glomerular diameter (micron) was increased in groups 2 (147 +/- 21), 3 (144 +/- 22), and 4 (150 +/- 7) compared with group 1 (104 +/- 12) (P less than .01). Glomerular hypertrophy was associated with an increase in the relative amount of mesangial matrix as determined by staining for fibronectin. By immunofluorescence microscopy (0-4+ scale), type I collagen antigen was not detected in the mesangium of any of the experimental groups. Staining for type V collagen and thrombospondin was similar between the experimental groups. Type III collagen antigen was not detected in the mesangium of control (group 1) or insulin-deficient diabetic rats (group 3); however, it was detected (2-3+) in the mesangium of both insulin-treated diabetic and nondiabetic rats (Mann-Whitney, P less than .01). Comparable intensity of staining (1+) for type IV collagen antigen was detected in the mesangium of animals from groups 1, 2, and 4; however, the staining intensity was markedly increased (3+) in insulin-deficient diabetic rats (group 3; Mann-Whitney, P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)