Vitamin A Homeostasis in the Diabetic Rat.

Abstract

SummaryThe concentrations of vitamin A (retinol) and retinyl ester in the plasma and liver of normal and diabetic rats were measured by HPLC (high-performance liquid chromatography). Diabetic rats had severe hyperglycemia, induced by a single streptozotocin injection 5 weeks prior to sampling. In the normal rats, plasma retinyl palmitate was very low, and the level was increased 10-fold by diabetes. Detailed timecourse studies showed that rats became hyperglycemic within 48 h of streptozotocin injection, yet the plasma retinyl palmitate level was not elevated until some three weeks later. Severe diabetes did not significantly influence plasma retinol; however, free retinol in the liver was elevated within 10 days of initiation of the disease and continued to increase for the duration of the study. These results show that streptozotocin-induced diabetes significantly alters the concentrations of hepatic retinol and plasma retinyl ester. The biochemical mechanism(s) of this altered vitamin A homeostasis in diabetes and its possible relationship to tissue pathogenesis are not known at present. Diabetes refers to metabolic disorders associated with hyperglycemia. Type I diabetes (juvenile-onset, insulin-dependent) is characterized by insulin deficiency; whereas in Type II diabetes (late-onset), the insulin level may be normal (or even elevated) but insulin is not effective in target organs. Various animal models have been developed to study the metabolic perturbations and underlying causes of diabetes mellitus [1,2]. In most of these experimental models, diabetes is induced