Electrolytes, water, RNA, total creatine and calculated resting membrane potential in muscle tissue from pregnant women

• <i>Background:</i> The nutritional situation of the fetus and pregnant woman is important for human health, but knowledge of how nutrition affects maternal metabolism and physiology during pregnancy is limited. Such knowledge is important, for example in body composition studies, when information about lean tissue composition is needed. Muscle, a main part of lean tissue, changes its composition in response to age and sex, but the effect of pregnancy on this composition is unknown. <i>Methods:</i> Muscle samples from 11 pregnant and 16 nonpregnant women were analyzed for water, electrolytes, total creatine, alkali-soluble protein (ASP), DNA and RNA. Plasma was analyzed for electrolytes. The amount of extracellular and intracellular water as well as the resting membrane potential (RMP) in muscle were calculated. <i>Results:</i> Pregnant women had lower plasma concentrations of potassium and sodium but higher muscle concentrations of sodium and water (total and extracellular) than nonpregnant women. RMP was more negative in pregnant than in nonpregnant women. Total creatine in muscle (per kilogram ASP) was increased during pregnancy. The muscle content of RNA (per kilogram DNA) was lower in gestational week 18 than in nonpregnant controls. <i>Conclusion:</i> Pregnancy influences muscle composition in several ways that are relevant for an increased understanding of interactions between nutrition and reproduction.

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