Effects of food restriction on systolic mechanical behavior of the ventricular pump in middle-aged and senescent rats

Previous work from our laboratory has revealed that the intrinsic contracti lity of the left ventricle is depressed in rats at 24 months, and the ventr icular internal resistance shows declines with age. The aim of this study w as to determine whether food restriction (FR) delays the development of age -related changes in left ventricular (LV) contractility and internal resist ance, Male Fischer 344 rats that began FR at the ages of 12 and 18 months w ere fed on alternate days for 6 months and compared with age-matched ad lib itum (AL)-fed rats. Rats studied at the ages of 18 and 24 months were refer red to as middle-aged and senescent rats, respectively, and were anesthetiz ed and thoracotomized. We measured LV pressure and ascending aortic flow wa ves by using a high-fidelity pressure sensor and an electromagnetic flow pr obe, respectively. The elastance-resistance model was used to generate E-ma x and Q(max) to describe the physical properties of the left ventricle; E-m ax is the maximal systolic elastance to represent the myocardial contractil ity; Q(max) is the theoretical maximal flow to be inversely related to the LV internal resistance. Neither age nor diet affected basal heart rate, LV end-systolic pressure, or cardiac output. E-max normalized to LV weight (E- maxn) exhibited a decline from 941.9 +/- 62.7 mmHg/ml-g to 690,2 +/- 57.5 m mHg/ml-g with age in AL-fed rats but not FR rats. Q(max) showed an increase with age from 36.55 +/- 2.78 ml/s to 44.22 +/- 2.62 ml/s in AL-fed rats or from 36.01 +/- 2.09 ml/s to 43.52 +/- 2.74 ml/s in FR rats. There was no e ffect of diet on Q(max). In conclusion, FR prevents or delays the reduction in myocardial contractility that occurred between is and 24 months of age in AL, rats. However, FR does not affect the age-related changes in ventric ular internal resistance.