Effects of constant light exposure on obesity in high fat diet rats

Abstract

Objective To observe the effects of constant light exposure on the obesity in high fat diet rats. Methods Thirty-two male SD rats were randomly divided into four groups : rats on a normal chow exposed to standard light-dark cycle (group A), rats on a normal chow exposed to constant light (group B), rats on a high fat diet exposed to standard light-dark cycle (group C), and rats on a high fat diet exposed to constant light (group D). Body weights and food intakes were recorded weekly throughout the 12-week study. Body weight, fat mass, visceral adipose tissue weight, intraperitoneal glucose tolerance test (IPGTT) results, insulin resistance parameters, serum lipids and levels of interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α) were compared among groups. Epididymal adipose tissues mRNA expression of circadian clock genes, i. e. clock, bmal1, rorα, rev-erbα, cry1, per1, and per2 were analyzed by realtime PCR. Results From the 9th week, body weights of rats in group D were significantly higher than those in group C (all P<0.05). At the 12th week, area under curve of IPGTT (AUC-IPGTT) in groups B, C, and D were significantly higher than that in group A. AUC-IPGTT in group D was significantly higher than that in group C (all P<0.05). Compared with group C, a significant increase in fat mass, visceral adipose tissue weight, homeostasis model assessment for insulin resistance, serum cholesterol, TNF-α levels were observed in group D (all P<0.05). And a significant decrease in quantitative insulin sensitivity check index (QUICKI) and high density lipoprotein-cholesterol were observed in group D in comparison with group C (both P<0.05). Circadian clock genes (clock, rorα, rev-erbα, cry1, per1) mRNA expressions in group B and D were significantly different from those in group A (all P<0.05) . Expression of cry1 in group D was significantly higher than that in group C. In group C, rev-erbα mRNA expression was significantly down-regulated in comparison with group A (P<0.05). Conclusion Constant light exposure exaggerates obesity, glycolipid metabolism abnormality, inflammation, and insulin resistance in high fat diet rats. (Chin J Endocrinol Metab, 2017, 33: 1057-1062) Key words: Constant light exposure; High fat diet; Obesity; Insulin resistance; Circadian clock disruption