Circadian Differences in Stress-Induced Pressor Reactivity in Mice

Abstract

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 (ϩ24% versus ϩ11% on stress day 3, light versus dark). The results suggest that a stress delivered during the nonactive phase represents a higher cardiovascular risk. Key Words: blood pressure Ⅲ heart rate Ⅲ corticosterone Ⅲ circadian rhythm L ifestyle stress is a risk factor for human diseases, including cancer, stroke, psychological disorders, and heart disease. There is a circadian pattern in the incidence of cardiovascular pathologies, with a higher frequency of heart attacks, strokes, and arrhythmias during the morning hours. [1][2][3] Stressful conditions may also be a precipitating factor in the occurrence of cardiovascular accidents.In animals, stress exposure produced by a variety of methods provokes a cascade of autonomic adjustments characterized by increased blood pressure (BP), increased heart rate (HR), and behavioral alterations. Most studies of stress biology have been conducted in rats, providing information on changes in cardiovascular function and eating and drinking behaviors. 4 -10 However, one complication of the experimental paradigms is that the stress effects can be enhanced by animal handling, noise, or pain, as seen in the forced swim test, air jet exposure, and physical restraint. 4,8,11 Shaker stress is a mild, pain-free stimulus that elicits reproducible changes in BP, HR, sympathetic activity, and stress hormone secretion. 12,13 There is no information on the application of shaker stress in mice and no data on the long-term effects of shaker stress on the cardiovascular system or on drinking and eating patterns.For investigations in mice, we developed a computerized system for chronic, continuous BP recording and combined this with electronic recording of licking activity for analysis of circadian patterns. 14,15 This methodology was applied to the investigation of the effects of stress on BP and HR responses and dri...

Comparison of the effects of acute and chronic psychological stress on metabolic features in rats

“…According to the previous studies, chronic exposure to stress led to different results in relation with the feed intake and weight gain. For instance, repeated immobilization in male Wistar rats (2 h daily, for 2 periods of 5 and 4 consecutive days, separated by 2 d of rest) (Ricart-Jane et al, 2002) and in male Sprague-Dawley rats (2 h/d, for 15 d) (Martí et al, 1993) decreased feed intake and weight gain, whereas intermittent shaker stress for 2-min periods (150 cycles/min), 45 times/d for 7 d in male C57BL6 mice increased water intake, induced no change in feed intake, and significantly decreased body weight (Bernatova et al, 2002). Repeated social stress (for 6 d) increased feed intake during the light period but decreased weight gain in male Sprague-Dawley rats (Bhatnagar et al, 2006).…”

Enhanced heart rate variability and baroreflex index after stress and cholinesterase inhibition in mice

“…Under ketamine-xylazine anesthesia (120:20 mg/kg im), mice were prepared with chronic carotid arterial catheters according to methods previously described (7,35). Heparinized saline (100 IU/ml) was continuously infused intra-arterially (25 l/h) to maintain catheter patency.…”

“…In many cases, the stressors are physical insults, such as restraint, exhaustive swimming, or electric footshock. We used a chronic stress model that combines shaking (a physical stimulus) with novelty (intermittent exposure) (7). It produces consistent, repeated increases in blood pressure (BP), HR, and corticosterone secretion (7,33).…”

Salt Appetite and the Renin-Angiotensin System

“…22,23 The system uses a microrenethane catheter covered with a metal spring that is attached to a swivel at the top of the cage. A heparinized saline infusion (80 U/mL, 25 L/h) is used to maintain catheter patency.…”