CIRCADIAN-RHYTHM OF SERUM AND LYMPH APOLIPOPROTEIN AIV IN AD LIBITUM-FED AND FASTED RATS

The aim of the present study was to determine if there is a circadian rhythm in serum and lymph apolipoprotein (apo) AIV and what factors de termine this rhythm. Male Sprague-Dawley rats with chronic right atria l catheter were housed in a room illuminated from 0600 to 1800. With a d libitum feeding, serum apo AIV concentration showed a circadian rhyt hm concomitant with the feeding pattern. In 24-h fasted rats, the seru m apo Ani concentration maintained a circadian rhythm and was high dur ing the dark. With mesenteric lymph diversion, serum apo AIV concentra tion diminished and the circadian rhythm was abolished. The lymph flow , lymph apo AIV, cholesterol, triacylglycerol, and phospholipid conten ts all exhibited the same circadian rhythm in fasting, with the levels higher in the dark. These circadian rhythms were abolished after bile diversion. In conclusion, serum apo AIV in ad libitum-fed and fasted rats exhibits a circadian rhythm governed by lymph apo AIV output. Fur thermore, bile was an important determinant of the circadian rhythm pf lymph flow, lymph apo AIV, triacylglycerol, cholesterol, and phosphol ipid output.