Morphometric studies of pancreatic islets and retinal vessels of rats with streptozotocin-induced latent diabetes.

Latent diabetes was induced in rats by injecting subdiabetogenic doses of streptozotocin. Four months later, the pancreas was examined and morphology, number and size of Langerhans islets were studied and compared with those of control and overt diabetic animals. In latent diabetics and in diabetics, islet surface per unit pancreas surface was significantly lower (p less than 0.01) than in controls. Immunoreactive insulin in beta cells was visualized by the peroxidase reaction and quantitated by densitometry. Assuming insulin in islets of controls equal to 100%, insulin in islets of latent diabetic rats was reduced to 38% (p less than 0.05) and in diabetics to 6% (p less than 0.01). Differences between latent and overt diabetics were not significant. At the same time occurrence of microangiopathy was taken in consideration and the basement membrane thickness of retinal capillaries was measured on electron micrographs by means of an image analyzer. Compared to controls, retinal capillary basement membranes of latent diabetics had increased by 49% (p = 0.01) and of diabetics by 68% (p less than 0.01). Differences between latent diabetics and diabetics were not significant. These observations demonstrate the induction of microangiopathic changes in rats in absence of hyperglycemia and of a genetic prediabetic disposition. Other mechanisms, possibly related to the induced islet abnormality, may be involved in the basement membrane thickening.