Effects of Feeding Levels and Body Weight Loading on Muscle Size and Visceral Organ Sizes in Rats

Abstract

The effects of feeding levels and body weight loading on the soleus muscle size and visceral organ sizes in rats were studied by using the whole-body suspension technique. Body suspensions in the free-feeding and chowrestraint conditions were maintained for 18 and 11 days, respectively. The rats were divided into three groups: cage control (CON), body suspended (BS), and BS plus continuous weight-bearing of the hind limbs on the floor of the cage (BSW). In the free-feeding conditions, the body weights of the BS and BSW rats decreased during the first 4 days. The initial loss of weight correlated with a reduced chow intake during this period. In the chow-restraint conditions, however, the body weight of BS and BSW rats decreased with prolongation of the suspension period, indicating that factors other than chow intake participated in the weight decrease. In both feeding conditions, the adrenal weights of the BS and BSW rats were 2 times higher than those of CON rats, suggesting that suspension stress may produce adrenal hypertrophy. The rectal temperatures of BS and BSW rats were also significantly higher than those of CON rats, showing that a higher metabolic state may be induced by suspension. In both feeding conditions, the weights and protein concentrations of soleus muscles of BSW rats were significantly higher than those of BS rats, suggesting that the weight bearing by the soleus muscles during suspension may maintain the size and protein levels of muscles.