Abstract 3292: Cardiac Dysfunction Induced By Chronic Restrain Stress Is Mediated By Opioid Receptors

Abstract

Psychological and physical stressors are a major health problem in our society. The effect of chronic stress on myocardial function has not been assessed. Our hypothesis is that chronic stress induces cardiac dysfunction and that its effect is mediated by activation of opioid receptors (OPR). Six week-old male ICR mice were restrained for 12 h with no food and water. This was followed by 12 h of rest with food and water provided ad labium. Unstressed (control) mice were kept in the original cage and were not given food and water during the stress period of the experimental group. Left ventricular performance was analyzed in mice anesthetized with 2% isoflurane using an ARIA pressure-volume conductance system (Millar Instruments). Our studies demonstrated for the first time that cardiac function was significantly depressed in restrained mice, as evidenced by a significant decrease in body weight (9%), heart rate (21%), stroke volume (38%), cardiac output (52%), ejection fraction (27%) and preload recruitable stroke work (43%). Systolic function (control vs. stressed group) (P<0.05), was 88 ± 2.2 vs. 68 ± 2.8 mmHg for end-systolic pressure, 6.1 ± 0.15 vs. 7.6 ± 0.15 μl for end-systolic volume, and 11,471 ± 913 vs. 5,860 ± 761 mmHg/s for +dP/dt. Diastolic function (control vs. stressed group) (P<0.05), was 2.9 ± 0.3 vs. 5.0 ± 0.5 mmHg for end-diastolic pressure, 17.1 ± 0.4 vs. 14.4 ± 0.5 μl for end-diastolic volume, 7,678 ± 419 vs. 4,195 ± 358 mmHg/s for -dP/dt, and 7.1 ± 0.5 vs. 10.8 ± 1.1 ms for tau (time constant of isovolumic relaxation). Peripheral vascular resistance (Ea) increased from 7.7 ± 0.2 in the control group to 9.8 ± 0.7 mmHg/μ l in the stressed group (P<0.05). Administration of an opioid antagonist naltrexone (8 mg/kg, i.p.) during each cycle of stress completely restored the cardiac function of stressed mice. Naltrexone alone had no effect on cardiac function in unstressed mice. These intriguing data suggest that opioid receptors are involved in the chronic stress-induced cardiac dysfunction and that treatment with an opioid antagonist can prevent this cardiac dysfunction.