on September 30, 2002
Published online before print September 30, 2002, doi: 10.1161/01.HYP.0000036405.27562.02
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Submitted on July 19, 2002
From the Department of Pharmacology and Toxicology, Wright State University School of Medicine (I.B., M.P.K., J.B.L., M.M.), Dayton, Ohio; and Institute of Normal and Pathological Physiology, Slovak Academy of Sciences (I.B.), Bratislava, Slovak Republic. * To whom correspondence should be addressed. E-mail: Mariana.Morris{at}wright.edu.
Abstract—The objective of this study was to determine the effect of chronic stress exposure on the circadian pattern of cardiovascular responses in mice. Using male C57BL6 mice with carotid arterial catheters, we tested the effect of 7 days of intermittent shaker stress on body weight, food intake, drinking activity, plasma corticosterone, mean arterial pressure (MAP), and heart rate. The stress was delivered automatically for 2-minute periods (150 cycles/min), 45 times/d for 7 days. Plasma corticosterone was significantly increased in acutely and chronically stressed mice, with a partial attenuation in the chronic condition. Stress increased water intake, produced no change in food intake, and significantly decreased body weight (5% change). MAP and heart rate were measured continuously on stress days 1, 3, and 7 and during the basal and recovery periods. Chronic stress did not produce a sustained increase in MAP; however, there was an increase in MAP during the first stress day and a decrease during the recovery period. There was a circadian pattern in the pressor responses, with greater increases seen during the light period (nonactive phase) than in the dark period (+24% versus +11% on stress day 3, light versus dark). The results suggest that a stress delivered during the nonactive phase represents a higher cardiovascular risk.
Revised on August 19, 2002
Circadian Differences in Stress-Induced Pressor Reactivity in Mice
Iveta Bernatova;
Key words: blood pressure • heart rate • corticosterone • circadian rhythm
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