Author Interviews, Circadian Rhythm, Gender Differences / 18.01.2019 Interview with: Lauren Douma, Ph.D. Postdoctoral Fellow University of Florida Department of Medicine Division of Nephrology, Hypertension, and Renal Transplantation Gainesville, FL 32610 What is the background for this study? What are the main findings?  Response: Our internal circadian clock not only controls our sleep/wake cycle, but also many other physiological functions including rhythms in body temperature, heart rate, and blood pressure. During the day when we are active our blood pressure peaks and at night when we are asleep our blood pressure dips. Certain individuals do not experience this dip in their blood pressure at night and are referred to as non-dippers. Non-dippers have an increased risk for heart and kidney disease. Previously, our lab has shown that if we knock out a core circadian clock gene (PER1) in male mice, they develop non-dipping hypertension on a treatment that mimics salt-sensitive hypertension. In the current study, we examined the effect of knocking out this circadian clock gene in female mice. We found that female mice without the PER1 gene do not develop the non-dipping hypertension that the males develop. Female mice without PER1 maintain their circadian rhythms of blood pressure, including the dip in their blood pressure at night even with the same treatment that the males received to mimic salt-sensitive hypertension. (more…)
Author Interviews, Circadian Rhythm / 28.11.2018 Interview with: Yujiro Yamanaka, Ph.D. Associate Professor Hokkaido University Graduate School of Education Sapporo, Japan What is the background for this study? Response: My laboratory has focused on the human circadian rhythms in particularly investigating the time of day effect of non-photic cues especially physical exercise and psychological stressor on circadian rhythms. In mammals including humans, the central circadian pacemaker is located in the suprachiasmatic nucleus (SCN) in the brain hypothalamus. The SCN entrains to an external light-dark cycle and generates endogenous 24 h rhythmicity in body function. The hypothalamic-pituitary-adrenal (HPA) axis is our major stress response system. We can assess the response of HPA axis to psychological stress event by measuring the level of glucocorticoid hormone, cortisol in saliva. The cortisol shows clear circadian rhythm with higher levels in the morning and lower levels in the evening. This rhythm is generated by the SCN circadian pacemaker. Previous study (Kudielka et al. Psychoneuroendocrinology 2004) could demonstrate that the cortisol stress level is significantly elevated by acute psychological stress event in the morning (9 a.m. to 10 a.m.) and afternoon (3 p.m. to 4 p.m.). However, there are no study examining the effect of evening psychological stress event on the HPA axis activity. Thus, our new study focused on examining whether the HPA axis differentially responses to morning and evening stress event in healthy subjects. (more…)