THE EFFECT OF EXCESS LEVELS OF VITAMIN A ON THE MORPHOLOGICAL AND BIOCHEMICAL CHARACTERISTICS OF RAT LIVER GOLGI APPARATUS (GLYCOSYLATION)

BERDINE R MARTIN, Purdue University

Abstract

Vitamin A toxicity in the liver may be correlated with an effect on subcellular oganelles, particularly on the Golgi apparatus. The effect of vitamin A on hepatic Golgi apparatus membranes has not been studied. Therefore, this study investigated the effects of high levels of Vitamin A on Golgi apparatus of rat liver under three conditions: (1) in vitro incubation of isolated Golgi apparatus with either 0.0002, 0.2, or 20 (mu)m retinol and retinyl palmitate compared to incubation with Triton X-100, a non-ionic detergent; (2) in vivo feeding of 4000 I.U. or 400,000 I.U. retinyl palmitate per kg diet for 16 weeks; and (3) gavaging with 0.5 ml olive oil or 0.5 ml olive oil with 40 mg retinol for each of three consecutive days. The specific activity of N-acetylglucosamine galactosyltransferase, (galtrans) a luminally oriented transmembrane protein, uridine 5'-diphosphate phosphatase (UDPase), a luminal protein, and NADH ferricyanide reductase, a cytoplasmically oriented electron transport protein was measured. Distribution of the forms of vitamin A present in Golgi apparatus membranes were analyzed by HPLC. Morphological characteristics were determined by electron microscopic analyses. In vitro excess levels of vitamin A did not exhibit a significant detergent-like effect on the three enzymes measured when compared to Triton X-100. Both long term in vivo feeding with retinyl palmitate and acute ingestion of retinol resulted in hepatic lipid accumulation which interfered with the isolation of a pure Golgi apparatus fraction and perhaps contributed to the apparent biochemical trends. Fat storing cells, observed in excess vitamin A tissue, coincided with the presence of an increased number and percent volume of lipid droplets in the Golgi apparatus and related fractions as well as a significant decrease in galactosyltransferase activity. Total vitamin A in Golgi apparatus membranes was negatively correlated (r = -0.70) with galtrans activity after chronic ingestion of retinyl palmitate. UDPase activity was stimulated under both in vivo regimens but did not exhibit a positive correlation with membrane vitamin A content. Thus, vitamin A toxicity may be related to reduced glycosylation and increased lipid accumulation in hepatic rat liver.

Degree

Ph.D.

Subject Area

Nutrition

COinS