Vitamin A palmitate decreases intravenous glucose tolerance in man

We tested retinyl palmitate for in vivo effects in man and in vitro effects on the IM-9 lymphocyte insulin receptor. Intravenous glucose tolerance tests (IVGTT) with 25 g glucose were performed on 10 healthy subjects before and after two intramuscular injections of retinyl palmitate (25,000 IU) 18 hours apart. In 9 of 10 subjects, glucose disposition was impaired after treatment with retinyl palmitate. In vitro, retinyl palmitate 10(-4) - 10(-6) M did not affect the binding or displacement of insulin 125I from lymphocyte receptors. We conclude that retinyl palmitate decreases glucose tolerance without demonstrable effects on insulin release or insulin binding to receptors.