SCHEDULE-INDUCED PSYCHOLOGICAL STRESS AND MOLECULAR-STRUCTURES OF CARDIOMYOCYTES

To establish a psychological stress model, we characterized in rats th e effects of chronic (5-6 wk) scheduled food pellet feeding (35 mg/80 s for 8 h/day). Because the scheduled intake of pellets required that rats have access to 80% of ad libitum intake, the effect of food restr iction was also examined by withholding food intermittently for 24 or 48 h each, followed by 24 h free access to food. Cardiac norepinephrin e concentration was significantly increased (1,076 +/- 169 vs. 693 +/- 107 ng/g, P < 0.05) in rats subjected to pellet feeding compared with pair-fed rats (same amount of pellets in one portion) or 24- or 48-h intermittently fasted rats; similarly, the epinephrine content of adre nal glands was increased (P < 0.05). Left ventricular rate of sarcopla smic reticulum Ca2+ uptake was decreased (P < 0.05) compared with pair -fed rats, reaching values observed for 24-h fasted rats, whereas the proportion of cc-myosin heavy chains was only slightly reduced. Thus t he schedule-induced stress arising from pellet feeding exhibits featur es of stress models involving physical pain and appears to stimulate t he adrenergic system with subsequent impairment of Ca2+ cycling that i s typical of various heart diseases.