Vitamin A Homeostasis in the Diabetic Rat

The 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 time-course 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.