Book of Abstracts - New Frontiers 2022

Abstracts of oral presentations

CONSEQUENCES OF CHRONODISRUPTION ON THE CIRCADIAN CONTROL OF CARDIOMETABOLIC PROCESSES

M. Zeman, V. S. Rumanova, H. Šutovska, Z. Dzirbíková, L. Molčan, M. Okuliarová

Comenius University in Bratislava, Faculty of Natural Sciences, Department of Animal Physiology and Ethology, Bratislava, Slovakia

Circadian rhythms allow organisms to predict regular changes in the environment and prepare to them in advance. They are important for the efficient functioning of the cardiovascular system and metabolism, which both exhibit pronounced daily rhythms. Artificial light at night (ALAN) is a new anthropogenic factor, increasing dramatically recently with possible adverse effects on health. Therefore, we explore the effects of ALAN on daily rhythms in cardiovascular parameters, selected metabolites, hormones, and clock and clock-controlled genes to evaluate the underlying mechanisms. We used normotensive and spontaneously hypertensive rats (SHR), which were exposed either to the control 12/12 light/dark cycle or to dim light (~2 lux) at night (ALAN) for 2 and/or 5 weeks. Bodyweight, food and water consumption were monitored, and metabolites and hormones were measured in plasma. Blood pressure (BP) and heart rate (HR) were measured continuously by radiotelemetry (DSI, USA) and circadian oscillations were evaluated. The expression of genes involved in the control of metabolism was measured in the brain, liver and abdominal fat over 24 h. In the central oscillator, suprachiasmatic nucleus (SCN) of the hypothalamus, we found the attenuated clockwork after ALAN exposure, because circadian rhythms of several clock genes had lower amplitude or were lost. Importantly, the rhythmic pattern of vasopressin, the dominant neurotransmitter and an output signal of the SCN, was suppressed in the SCN and eliminated in the circulation, which was reflected in disturbances of drinking behavior. Glucose and lipid metabolism is under strong circadian control and therefore, we determined daily rhythms of plasma glucose, triacylglycerols, cholesterol and metabolic hormones, and the expression levels of genes involved in the control of metabolism. All three plasma metabolites lost their rhythms after 2 weeks of ALAN. Moreover, melatonin rhythm, which transmits information about the natural night over the internal milieu of the body, was lost and the plasma corticosterone rhythm was suppressed and phase-advanced after ALAN exposure. These complex changes can have serious consequences on the timing of physiological processes and stress response, with negative consequences on health. Further, ALAN attenuated insulin sensitivity in SHR rats, which are genetically insulin resistant, therefore diabetic patients might be more sensitive to chronodisruption than healthy individuals. Moreover, rhythmic response of BP and HR to the norepinephrine challenge was attenuated by ALAN, which enhanced the pressor response after 5 weeks of exposure. In conclusion, functioning of the circadian system was compromised by ALAN, showing the impact on the cardiovascular system and metabolism. Chronodisruption can have more pronounced consequences for hypertensive individuals and therefore comorbidities should be considered when consequences of light pollution on human health are evaluated.

Keywords: circadian, daily, melatonin, corticosterone, clock

Funding: Supported by grant APVV-17-0178 and VEGA 1/0492/19.

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