The influence of temporal food restriction on the performance of isolated cardiac muscle

In this study we assessed the mechanical function of isolated left ventricu lar papillary muscles from 60 day-old male Wistar-Kyoto rats (WKY) subjecte d to different periods of food restriction (FR). The food-restricted animal s (R) were fed 50% of the amount of diet consumed by the ad Libitum-fed rat s (C). The cardiac muscles were studied after 30, 60, and 90 days (R-30, R- 60 and R-90) of FR. The effect of FR on myocardial collagen concentration w as also evaluated. The parameters from the three control groups that were s tatistically identical were combined and the control pool group (CP) was fo rmed. The left ventricular weight-to-body weight ratio was lower in the R-3 0 and higher in the R-60 and R-90 in relation to their control groups. Hydr oxyproline concentration was higher only in R-90 compared to CP and R-30. M yocardial mechanical function was the same in the C groups. The comparisons between CP and FR groups showed that: the muscles of R-30 presented increa sed resting tension and maximum rate of tension decline, and decreased velo city of shortening; the muscles of R-60 and R-90 groups showed a prolongati on of the time to peak tension (TPT) and the time to peak shortening (TPS); and R-30 had an increased time from peak tension to 50% relaxation (RT1/2) . Increases in TPT, TPS, and RT1/2 in groups R-60 and R-90 were significant in relation to R-30. In conclusion, while FR for 30 days produces disparat e effects on myocardial performance, FR for 60 and 90 days prolongs the con traction period. The change of relaxation time in R-90 might be related to the increased myocardial collagen content. (C) 2001 Elsevier Science Inc. A ll rights reserved.