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Title: Light and diurnal cycle affect human heart rate: Possible role for the circadian pacemaker
Author(s): F.A.J.L. Scheer, L.J.P. van Doornen and R.M. Buijs
Journal: Journal of Biological Rhythms
Year: 1999
Volume: 14
Issue: 3
Pages: 202--212
Publisher address: Netherlands Inst Brain Res, Project Grp Hypothalam Integrat Mechanisms, NL-1105 AZ Amsterdam, Netherlands Free Univ Amsterdam, Res Grp Psychon, Amsterdam, Netherlands
ISSN: 0748-7304
File URL: vuams-pubs/Scheer_1999.pdf
Keywords: Affect, Animals, BLOOD-PRESSURE, cardiovascular, Circadian Rhythm, constant routine, endogenous, Heart, Heart Rate, HEART-RATE, Humans, Hypertension, HYPERTENSIVE RATS, illumination, Light, LOCOMOTOR-ACTIVITY, masking, Melatonin, MELATONIN SUPPRESSION, MEN, MESSENGER-RNA, Netherlands, NEURAL CONTROL, NEURONS, physiology, RHYTHM, SCN, secretion, SUPRACHIASMATIC NUCLEUS CELLS, Time
Abstract: Humans and animals demonstrate diurnal rhythms in physiology and behavior, which are generated by the circadian pacemaker, located in the suprachiasmatic nucleus (SCN). The endogenous diurnal rhythm of the SCN is synchronized to the diurnal cycle most effectively by light. However, light also influences the SCN and its output instantaneously, as is demonstrated for the immediate effects of Light on SCN neuronal firing frequency and on the output of the SCN to the pineal, inhibiting melatonin secretion. In addition to this, the circadian pacemaker modulates neuronally also other organs such as the adrenal. Therefore, the authors investigated the effect of this light input to the SCN on human heart rate, using Light at different phases of the day-night cycle and light of different intensities. Resting heart rate (HR) was measured in volunteers between 20 and 40 years of age during supine, awake, resting conditions, and after 2 hours of fasting. In Experiment 1, HR was measured at different times over the day-night cycle at 0 lux and at indoor light. In Experiment 2, HR was measured at different times over the day-night cycle at controlled light intensities of 0 lux, 100 lux, and 800 lux. The authors demonstrate a clear diurnal rhythm in resting HR in complete darkness, similar to that measured under constant routine conditions. Second, it is demonstrated that light increases resting HR depending on the phase of the day-night cycle and on the intensity of light. These data strongly suggest that the circadian pacemaker modulates human HR

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