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.