Key result
Daytime blue light lowers systolic BP in normotensive rats and HR in hypertensive rats.
Why the study?
Short waves perceived as blue light are the strongest synchronizing agent for the circadian system, but their impact on cardiovascular rhythms, electrolyte excretion, and melatonin secretion under daytime exposure required investigation.
Does daytime exposure to monochromatic blue light alter cardiovascular circadian rhythms, electrolyte excretion, and melatonin production in normotensive and hypertensive rats?
Does daytime exposure to monochromatic blue light alter cardiovascular circadian rhythms, electrolyte excretion, and melatonin production in normotensive and hypertensive rats?
Prolonged daytime exposure to monochromatic blue light alters cardiovascular circadian rhythms, electrolyte excretion, and melatonin production in both normotensive and hypertensive rats.
Rat data warrant no clinical light interventions; leaves open human translation of blue light effects on circadian BP/HR.
Artificial light is characterized by certain features of its impact on the body in terms of its spectral distribution of power, duration of exposure and intensity. Short waves, perceived as blue light, are the strongest synchronizing agent for the circadian system. In the present work, we investigated the features of the circadian rhythms of blood pressure (BP), heart rate (HR), the excretion of electrolytes and the secretion of melatonin in normotensive (Wistar-Kyoto) and hypertensive (SHR) rats under the action of monochromatic blue light in the daytime period. It was found that the exposure of Wistar-Kyoto rats to monochromatic blue light was accompanied by a significant decrease in nighttime and 24 h systolic BP. The most remarkable changes are characteristic of the HR in SHR rats under monochromatic light. A significant decrease in HR in each time period was found, but the predominance of nighttime over daytime values remained in SHR animals. There was also a significant increase in the mesor of the HR in SHR rats. Additionally, the amplitude of diastolic BP and HR, as well as the range of oscillations in HR, were significantly increased compared with the standard light pattern. In contrast to SHR rats, the regulation of the circadian rhythms in Wistar-Kyoto rats was more flexible and presented more changes, which may be aimed at the adaptation of the body to environmental conditions. For Wistar-Kyoto rats, an increase in the level of excreted electrolytes was observed under the action of monochromatic light, but no similar changes were found in SHR rats. For Wistar-Kyoto rats, a significant decrease in the urine concentration of aMT6s in the daytime and nighttime periods is characteristic, which results in the loss of the circadian rhythm. In SHR rats, there was a significant decrease in the nighttime content of aMT6s in the urine, while the daytime concentration, on the contrary, increased. The obtained data demonstrate that prolonged exposure to monochromatic blue light in the daytime period affects the circadian structure of the rhythms of the cardiovascular system, the rhythm of electrolyte excretion and the production of epiphyseal melatonin in wild-type and hypertensive animals. In SHR rats, the rhythms of BP and HR exhibit a more rigid pattern.
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Bryk et al. (2022) studied Normotension and hypertension (animal model). Monochromatic blue light vs. Standard light pattern was evaluated on Circadian rhythms of blood pressure, heart rate, electrolyte excretion, and melatonin secretion. Daytime exposure to monochromatic blue light significantly decreased nighttime and 24-h systolic BP in normotensive rats and decreased HR across all time periods in hypertensive rats.
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