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ARS Home » Plains Area » Houston, Texas » Children's Nutrition Research Center » Research » Publications at this Location » Publication #72396
Title: FOOD INTAKE ALTERS MUSCLE PROTEIN GAIN WITH LITTLE EFFECT ON NA,K-ATPASE AND MYOSIN ISOFORMS IN SUCKLED RATS.

Author
item FIOROTTO, MARTA - BAYLOR COLL OF MEDICINE
item DAVIS, TERESA - BAYLOR COLL OF MEDICINE

Submitted to: American Journal of Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: During early life muscles enlarge and their composition changes resulting in their functional maturation. The question has been whether these two features are related. We altered the growth of rat pups by varying how much milk they drank. This was done by suckling the pups in litters of 4 (overfed), 10 (normal), or 16 (underfed) from birth to 21 d of age. We then examined if the biochemical composition of muscles differed depending on how much each pup ate, and if this was related to the size of the muscle. Muscle size was determined from the proteins that are critical for muscle function. We found that the more pups ate, the larger their bodies and muscles grew, but the muscles' composition was minimally altered. Thus, food intake is likely to influence only those aspects of muscle function related to size (e.g. strength) and not those related to composition (e.g. speed of contraction, and fatigue). Because rats are born at an earlier stage of development than humans, our findings are relevant to the growth of the human from approximately the third trimester of pregnancy through the fist six months of life. The data suggest that the amount of nutrients received by an infant can significantly alter how much muscle it deposits, but that this is likely to have a minimal effect on how the muscles work. We do not know, however, whether there are any long-term effects.

Technical Abstract: Biochemical maturation accompanies the rapid accretion of skeletal muscle in early life. We examined whether changes in muscle protein accretion, induced by variations in food intake altered the biochemical maturation of the soleus and the extensor digitorum longus (EDL) muscles. Rat pups were suckled in litters of 4, 10, or 16 from birth to induce differences in food dintake. At 21 d of age, muscle protein and DNA were quantitated and biochemical maturation was assessed from measurement of (3H)ouabain-binding site abundance and myosin isoform composition. Litter size alteration resulted in a twofold range in body and muscle weights, protein and DNA contents; protein accretion in the soleus was more responsive than in the EDL. Serum 3-5,3'-triiodothyronine (T3) and insulin concentrations decreased with increasing litter size. Total ouabain-binding sites were not altered in either muscle, and were independent of muscle size. Myosin isoform composition was minimally altered and more evident in the soleus. Thus, although postnatal muscle protein accretion was highly sensitive to food intake, biochemical maturation was resistant to these differences in growth rate and the accompanying endocrine effects.