A Diurnal Variation of Hepatic Lipogenesis in Chicks

Abstract

The existence of diurnal rhythm in both protein and carbohydrate metabolisms in different tissues of avian species and mammals has been demonstrated by many researchers1). As to a rhythmic change in lipid metabolism, it has been shown that cholesterol synthesis in the liver2) and intestinal mucosa3) of rats possesses a diurnal rhythm and that this rhythmic change is associated with a change in the activity of 3-hydroxy-3-methylglutaryl-CoA reductase [EC 1. 1. 1. 34], the rate-limiting enzyme for cholesterol synthesis4,5). Moreover, PEARCE6) has indicated an apparent diurnal rhythm in fatty acid synthesis in the liver and adipose tissue of laboratory rodents, although the periodic fluctuation in the activity of the rate-limiting enzyme for fatty acid synthesis has not been examined. In avian species, however, the rhythmic change in lipid metabolism has been studied less, with the exception of the changes in the activities of hepatic and intestinal 3-hydroxy-3-methylglutaryl-CoA reductases7).It is well known that fatty acid synthesis plays an important role in lipid metabolism and that the liver is a major site of fatty acid synthesis in chicks6). Therefore, this investigation was carried out to examine the existence of diurnal variation in fatty acid synthesis and lipogenic enzyme activities in the liver of chicks. Materials and Methods AnimalsSingle-Comb White Leghorn male chicks were used and fed a commercial chick starting ration from day-old until they reached a body weight of approximately 340g. The chicks were kept on a 12 hour light-12 hour dark cycle with Feed and water were given ad libitum throughout the test period. Hepatic fatty acid synthesis and lipogenic-enzyme activities were measured at intervals of 4 hours over a 24 hour period.