Dim light at night weakens daily heart rhythms and reduces melatonin in rats

ALAN significantly suppressed the 24-h variability in heart rate, blood pressure, and spontaneous baroreflex sensitivity after 2 weeks.

• After 5 weeks of ALAN exposure, the parameters showed partial restoration of 24-h variability.
• The blood pressure response to norepinephrine was reduced after 2 weeks and restored after 5 weeks.
• ALAN increased the blood pressure response to norepinephrine compared to control levels after 5 weeks.
• Increased expression of endothelial nitric oxide synthase was observed in arteries after 2 weeks but not after 5 weeks.
• Plasma melatonin levels were suppressed after both 2 and 5 weeks of ALAN exposure.
• Spontaneous exploratory behavior was reduced during the study.

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