Circadian differences in stress-induced pressor reactivity in mice

Area of Science:

• Cardiovascular Physiology
• Stress Physiology
• Chronobiology

Background:

• Chronic stress is a significant risk factor for cardiovascular disease.
• Understanding the circadian influence on stress-induced cardiovascular changes is crucial.
• Previous research has not fully elucidated the impact of chronic stress on the daily rhythms of cardiovascular function.

Purpose of the Study:

• To investigate the effect of chronic intermittent stress on the circadian patterns of cardiovascular responses in mice.
• To assess changes in body weight, food intake, drinking activity, and plasma corticosterone levels under chronic stress.
• To analyze the impact of chronic stress on mean arterial pressure (MAP) and heart rate throughout the day-night cycle.

Main Methods:

• Male C57BL6 mice were subjected to 7 days of intermittent shaker stress.
• Cardiovascular parameters (MAP, heart rate) were continuously monitored.
• Body weight, food intake, drinking activity, and plasma corticosterone were measured.
• Stress was applied automatically for 2-minute intervals, 45 times daily.

Main Results:

• Chronic stress partially attenuated the increase in plasma corticosterone compared to acute stress.
• Stress led to increased water intake, decreased body weight, but no change in food intake.
• No sustained increase in MAP was observed, but acute increases occurred on day 1, with a decrease during recovery.
• Pressor responses exhibited a circadian pattern, with significantly greater increases during the light (nonactive) phase compared to the dark (active) phase (+24% vs. +11% on day 3).

Conclusions:

• Chronic stress alters cardiovascular and metabolic parameters in mice.
• The timing of stress exposure is critical, with nonactive phase stress posing a higher cardiovascular risk.
• Circadian disruption by stress may underlie increased cardiovascular risk during specific phases of the daily cycle.