The Relationship between Lipoprotein Lipase Activity and Respiratory Quotient of Rats in Circadian Rhythms.

Abstract

Plasma lipid levels and lipoprotein lipase (LPL) are known to follow circadian rhythms in rats. However, very little information is available on the variations in respiratory quotient (RQ) during the 24-h period in rats. The aims of this study were to provide an overall view of the effects of circadian rhythm on RQ and to determine the relationship of LPL and RQ with metabolic parameters in these animals. Male rats were fed ad libitum and were kept under a 12 : 12-h light-dark cycle. Rats were killed every 2 h over a 24-h period for measurement of metabolic parameters and tissue LPL activity. The RQ was measured every 4 h over the same 24-h period. The gastric contents increased during the dark phase and decreased during the light phase. For the metabolic parameters, circadian rhythms were detected for plasma glucose, triglycerides, high-density lipoprotein cholesterol and non esterified free fatty acids, but not for plasma total cholesterol or phospholipids. The RQ and adipose tissue LPL activity increased during the dark phase, while skeletal muscle LPL activity decreased during this phase. The RQ was inversely correlated with skeletal muscle LPL activity (r‫)088.0؊؍‬ and positively correlated with adipose tissue LPL activity (r‫.)739.0؍‬ These results appear to show that rats tend toward consumption of fat by accelerating fat oxidation, resulting in suppression of fat accumulation in the light phase, while tending toward fat accumulation by the suppression of fat oxidation in the dark phase.

Leptin-sensitive neurons in the arcuate nuclei contribute to endogenous feeding rhythms

“…RER results are consistent with the circadian distribution of feeding and fasting in B-SAPs, associated with increased fat metabolism and lower RER during the fasting state than in the postingestive state, and with the absence of circadian feeding rhythms in the Lep-SAP group. In contrast, the continuously feeding (arrhythmic) Lep-SAP rats had higher RER values (Ͼ1.0) throughout the circadian cycle, consistent with their persistent postingestive state, high carbohydrate diet of rat chow and body weight gain (33,46,49,50,79,83,85). Overall, the RER was 0.903 Ϯ 0.005 for B-SAP rats during the day and 0.929 Ϯ 0.005 during the night (P Ͻ 0.001).…”

Circadian rhythms in glucose and lipid metabolism in nocturnal and diurnal mammals

“…The activity of LPL displays a diurnal variation with a phase which is opposite between adipose tissue and skeletal muscle in a given species. In nocturnal rats for instance, LPL activity increases during the dark period in adipose tissue (i.e., leading to accelerated fat accumulation), while its activity increases during the light period in the skeletal muscles (i.e., to support increased fat uptake and oxidation) (Tsutsumi et al, 2002). Circulating levels of FFA show an elevation during the light period (i.e., during fasting) and decline during the dark period (i.e., during feeding) in nocturnal rats and mice Stavinoha et al, 2004;Tsutsumi et al, 2002).…”

“…In nocturnal rats for instance, LPL activity increases during the dark period in adipose tissue (i.e., leading to accelerated fat accumulation), while its activity increases during the light period in the skeletal muscles (i.e., to support increased fat uptake and oxidation) (Tsutsumi et al, 2002). Circulating levels of FFA show an elevation during the light period (i.e., during fasting) and decline during the dark period (i.e., during feeding) in nocturnal rats and mice Stavinoha et al, 2004;Tsutsumi et al, 2002). Abrogation of the daily plasma FFA rhythm in rats with a bilaterally ablated SCN indicates the involvement of the central clock in daily changes in plasma FFA (Yamamoto et al, 1987).…”

Regulation of Fatty Acid Metabolism by Cell Autonomous Circadian Clocks: Time to Fatten up on Information?

“…Rhythms in lipoprotein-associated triglyceride hydrolysis could potentially contribute toward oscillations in circulating triglycerides. Lipoprotein lipase (LPL) activity demonstrates distinct time of day-dependent oscillations in peripheral tissues, which are essentially antiphase in muscle compared with adipose tissue (48). LPL activity appears to be under direct circadian clock control (49).…”

“…skeletal muscle, heart). Increased LPL activity in muscle (coupled with decreased activity in adipose tissue) at this time will promote channeling of lipoprotein-derived FAs to muscle (48). Transcriptional responsiveness of peripheral tissues to FAs increases at the beginning of the active phase, resulting in rapid induction of enzymes promoting FA ␤-oxidation, thereby increasing the capacity to utilize this carbon source for ATP generation (65).…”