The effects of diabetes on the vitamin A metabolism were studied. The concentrations of plasma retinol and retinyl ester were measured in diabetic patients using high-performance liquid chromatography (HPLC). In diabetic patients, the mean level of retinyl ester was significantly elevated compared to that of normal subjects (diabetes, 68.3 +/- 42.5 IU/100 ml of plasma; study I, 87.6 +/- 64.3 IU/100 ml of plasma; study II vs. normal, 29.8 +/- 10.3 IU/100 ml of plasma). The ultracentrifugal and column chromatographic studies were carried out to examine the distribution of retinyl ester in patient's plasma.
Retonol esters → hydrolysis by pancreatic enzymes to retinol. b-caroten is cleaved to retinal by b-carotene 15,15´ dioxygenase (cofactors iron and bile salts). Intestinal cells → esterification of retinol → transported in chylomicrons. Remnants of chylomicrons → liver→ esterification (if the concentration exceeds 100 mg, esters are stored ). Transport of retinol to target organs tightly bound to retinol-binding protein, RBP.