Cellular development of skeletal muscle of rats during recovery from prolonged undernutrition.

The cellular basis for growth retardation of skeletal muscle was studied in male Sprague-Dawley rats. At birth, animals were assigned to control (C) or food-restricted (R) groups. During lactation, food intake of the pups was reduced by limiting intake of the mother to 50% of controls. After weaning, pups received 40% of ad libitum intakes until 120 d of age. From 120 to 316 d, all animals were fed ad libitum. At 120 d, body weight of the R group was 41% of C and muscle and adipose weights were 54 and 16% of C, respectively. Muscle DNA in the R group was 47% of C, but protein-to-DNA ratio was normal. Fiber number was not different between C and R groups; however, muscle length and fiber cross-sectional area were 85 and 64%, respectively, of C values. After 196 d of recovery, weights of the body, skeletal muscles and adipose tissues averaged 76, 84 and 51% of C values, respectively. Recovery of skeletal muscle paralleled the recovery of fiber cross-sectional area (84%) and DNA content (86%). Daily injections of 100 micrograms of growth hormone from 120 to 148 d produced no additional recovery. This study establishes that growth retardation of skeletal muscle is associated with reductions in the development of cross-sectional area and DNA content of muscle fibers.