Hepatic Uptake of Vitamin A is Independent of Retinoic Acid Pretreatment in Neonatal Rats

Abstract

Previous studies have shown that total retinoid concentration in the liver of neonatal rats would increase in response to the VARA supplementation, which is a combination of vitamin A (VA) and retinoic acid (RA). Later studies have further demonstrated that a single dose of VA may stimulate the hepatic uptake, which in turn, significantly elevated the liver total retinol concentration. In current study, we gave the neonatal rats the RA treatment prior to the VA supplementation, and examined the distinct effect of RA on VA metabolism and kinetics in the liver tissue of these young animals. Sprague‐Dawley male and female rats were mated, and the dams were fed a VA‐marginal diet (0.35 mg retinol equivalents/kg diet) and were allowed to consume food and water ad libitum. On postnatal day (P) 2 and 3, pups from experimental group received an oral dose of RA (0.625μg/g body weight), while other pups received canola oil as the control treatment. Then, an oral dose of VA (6 μg retinyl palmitate/g body weight), containing 2 μCi of [3H]‐retinol as a tracer, was administered to all pups on P4. Pups (n = 4–6/treatment/time point) were euthanized from 25 min to 30 h, a total of 12 time points, after dose administration and the liver were collected. Tissue total retinoid mass was determined by ultra‐performance liquid chromatography (UPLC), and the tissue tracer level was measured by liquid scintillation counting. Results showed that in both oil‐pretreated and RA‐pretreated groups, the fraction of retinyl ester and retinol entering the liver increased continuously and peaked at 10 h. After that, the fraction of retinol slightly declined and remained at the same level until the end of the study. However, the fraction of retinyl ester decreased gradually until the 20hr time point and showed a trend of increase afterward. At the same time, liver vitamin A content of both groups increased gradually and peaked firstly at 10 h, after a slight decrease it reached a second peak at 20 h and declined in the following period of time. In conclusion, our findings indicate that liver uptake of dietary vitamin A may be tightly controlled and would not be affected by RA supplementation.Support or Funding InformationNIH grant HD006982