Response to the photoperiod in the white and brown adipose tissues of Fischer 344 rats fed a standard or cafeteria diet.

Researchers are identifying new factors that contribute to the obesity epidemic, with changes in the photoperiod as one promising risk factor. To study the influence of the photoperiod on adipose tissue, Fischer 344 rats were treated for 14 weeks with a long day (18 h light:6 h dark; LD) or a short day (6 h light:18 h dark; SD) and fed a standard diet (STD). Biometric measures, postprandial plasmatic parameters, gene expression in the retroperitoneal white adipose tissue (RWAT) and brown adipose tissue (BAT) and histology of the RWAT were analyzed. A second experiment with the same conditions and analysis was performed for 11 weeks with rats fed a cafeteria diet (CAF). In the STD experiment, the SD increased triglycerides and showed a tendency to reduce fat compared to the LD. In the RWAT, genes implicated in adipogenesis, lipogenesis and lipolysis were down-regulated, and the histological results showed a higher percentage of small adipocytes in the SD without changes in their total number. In the CAF experiment, lipogenesis and adipogenesis gene expression was increased in the SD, while adipocytes were smaller and their number increased. Both experiments showed in the SD a decrease in the BAT expression of lipid uptake and β-oxidation genes, while only the STD additionally showed a reduction in Ucp1 expression. In conclusion, the RWAT morphology and the expression of key genes for lipid metabolism in RWAT and BAT were influenced by the photoperiod; however, the changes observed in the RWAT were different depending on the diet.