The role of muscle in extrarenal electrolyte metabolism in the newborn
Nichols, B.L.; Rudolph, A.J.; Hazelwood, C.F.
Johns Hopkins Medical Journal 131(3): 212-219
1972
ISSN/ISBN: 0021-7263 PMID: 5075524 Document Number: 46849
Needle biopsy samples of 10 mg quadriceps muscle were obtained from 6 normal infants at birth and at age 24 h and from 5 of the infants at 48 h. Water, fat, dry matter, Na, K, Cl and the major N fractions, water soluble or sarcoplasmic, alkali soluble or myofibrillar and collagen were estimated. Also recorded were bodyweight, haematocrit and cumulative intakes of water, energy, minerals and N. Water, Cl and collagen N did not change significantly with age. The other N fractions on a fat-free basis were higher at 24 h than at birth and did not change significantly between 24 h and 48 h. On a fat-free dry basis muscle K rose from birth to 24 h and from 24 h to 48 h and muscle Na declined between birth and 24 h and then rose significantly at 48 h. Results obtained in a previous study of children aged 16 months, 45 months and 16 years are tabulated and the comparison showed that immature muscle contains more water and on a fat-free dry basis 50% less K and 50% more Na than mature muscle. Chloride space was estimated and used for the calculation of ion and water distribution in muscle. Published observations on the total water, Na and K in the infant body and total mass of muscle as a percentage of bodyweight were used to calculate the role of muscle in the extrarenal adjustment in electrolyte metabolism. It was concluded that muscle contributes to the postnatal expansion of extracellular fluid by a Na flux but does not seem to participate in the transfer of water to the extracellular fluid.