I. All food was withdrawn from male weanling rats until a 40 % loss of body-weight was attained. Another group of animals was treated similarly and then refed a stock diet until the original body-weight was attained.2. The body-weight loss caused a significant reduction in the weight of the heart, kidney, liver and epididymal fat pads. Refeeding produced a return to the control weight of the heart and kidney, an increase in the weight of the liver and a deficit in the weight of the epididymal fat pads.3. Body-weight loss caused a decrease in the weight of the three different muscles studied, and in the number and diameter of the fibres in each muscle. Refeeding restored the weight and cellularity of two of the three muscles to that of the control animals. The soleus muscle was heavier in the refed animals when compared to controls due to an increased fibre diameter.4. It is concluded that the decrease in the number and diameter of muscle fibres during starvation in the rat can be restored on refeeding a stock diet.A restriction in food intake causes a reduction in growth rate which produces a decrease in the transverse dimensions of skeletal muscle fibres in humans (Cheek et al. (Stickland et al. 1975). The effects of severe restrictions of food intake, producing a loss of body-weight, on the number and size of skeletal muscle fibres have been studied less extensively. Goldspink (1965) and Rowe (1968) reported a decrease in diameter but no change in the number of fibres when muscle weight of mice was reduced due to severe food restrictions. However, Layman (1978) reported a reduction in both fibre number and fibre diameter in muscles from rats deprived of all fo0d.A recent study in our laboratory examined three muscles (soleus, plantaris and biceps brachii) in young rats, rabbits, guinea-pigs and hamsters who underwent a 35-45% loss in body-weight due to a total withdrawal of food (Kim & Hegarty, 1978). A decrease in muscle fibre number due to starvation was observed in all three muscles from the rat and in the biceps brachii muscle from the hamster. Starvation produced no decrease in the number of fibres in any of the muscles from the rabbit or the guinea-pig.Montgomery ( 1979). Therefore, the response of muscle fibres to a total starvation and subsequent recovery when rats were fed on an adequate diet was studied in the present investigation. The number and diameter of fibres were simultaneously measured as an index of cellularity changes in different muscles. The use of DNA to extrapolate cell number and cell size was not considered because of difficulties in interpretation of cell number from DNA measurements (Sands et al. 1979;Layman et al. 1980).
1. Milk Sprague-Dawley rats were allocated at 100 g into either an adlib.-fed control group or a food-restricted group. The restricted group was fed for 9 d at 25% of ad lib. intake. Controls were killed at a body-weight of 100 g and 29 d of age and the restricted animals were killed at 70 g and 38 d of age.2. The effects of food restriction on muscle weight, fibre number, fibre diameter, DNA, and protein were examined in three skeletal muscles, the soleus, plantaris and extensor digitorurn longus (EDL).3. Acute dietary restriction caused body-and muscle-weight loss and a decrease in both the number and cross-sectional area of muscle fibres in each of the muscles.4. The restriction halted growth-related increases in DNA in all muscles and decreased the protein: DNA value in the plantaris and EDL.5. These results indicate that present theories describing cellular development are not adequate to define growth potential or growth retardation of skeletal muscle.
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