The influence of altered light–dark cycles on circadian rhythms of blood biomarkers in Wistar rats

= 40/group) for a period of 21 days. The control group was housed under a standard 10:14h light-dark schedule (lights on: 08:00). Group I was exposed to continuous illumination (dark deprivation). Group II underwent a shift-work-like lighting regimen, consisting of 24-h light exposure followed by 2 days of a standard light-dark cycle. A three-week exposure resulted in the disappearance of statistically significant daily fluctuations for most of the studied parameters. In addition, most biochemical parameters showed statistically significant changes in the characteristics of the circadian rhythm: an acrophase shift and an increase or decrease in amplitude, with the exception of LDH and creatinine, for which no significant rhythms were detected in the experimental groups. This study demonstrated that both experimental lighting regimens significantly altered the values of the investigated parameters, with more pronounced effects observed under the simulated shift-work schedule.