Food restriction impairs myocardial inotropic response to calcium and beta-adrenergic stimulation in spontaneously hypertensive rats
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Although long-term food restriction (FR) has been shown to induce cardiac remodeling and dysfunction, there arc few data on the effects of FR on pressure-overloaded hearts. The aim of this study was to examine the effects of FR on cardiac muscle performance during inotropic stimulation in the myocardium of spontaneously hypertensive rats (SIIRs). Male 60-day-old SHRs were subjected to FR for 90 days. Food-restricted animals received 50% of the ad libitum amount of food consumed by the control group. Myocardial function was studied in isolated left ventricular papillary muscle tinder isometric contraction in basal condition (1.25 mmol/L extracellular Ca2+ concentration) and after 3 inotropic maneuvers: (1) at postrest contraction of 30 seconds, (2) at extraccllular Ca2+ concentration of 5.2 mmol/L, and (3) after beta-adrenergic stimulation with 10 (6) mol/L isoproterenol. At basal condition, little from peak tension to 50'% relaxation was greater in the food-restricted group (P <.05). Inotropic stimulation with postrest contraction and isoproterenol promoted a significant lower increase of developed tension, maximum rate of tension development, and maximum rate of tension decline in the food-restricted compared to the control group. The elevation of extraccllular Ca2+ concentration induced a lower increase of developed tension, maximum rate of tension development, and time from peak tension to 50'% relaxation in the food-restricted than in the control group. In conclusion, long-term FR promotes impairment of myocardial inotropic response to calcium and beta-adrenergic stimulation in SHRS. (C) 2003 Elsevier B.V. All rights reserved.
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