Perinatal Nitrogen Accretion in Muscles and Fingernails

Abstract

Summary: Paired triceps muscle and fingernail samples were obtained at autopsy from 25 normally grown (NG) and 16 intrauterine growth-retarded (IGR) neonates who died within 28 days of birth. Gestational ages ranged from 21–46 weeks and birth weights ranged from 425–3750 g. Muscle samples were desiccated, defatted and ground to powder. Nitrogen content of muscle and fingernail were determined by a modified micro-Kjeldahl technique. Muscle nitrogen (MN) content averaged 12.1 ± 1.89 g/100 g fat-free dry solids (FFDS) (mean ± SD) and was similar for NG and IGR neonates and, within these two groups, for premature and mature babies. Fingernail nitrogen (FN) content averaged 13.8 ± 0.95 g/100 g and no variations with duration and quality of intrauterine growth were identified. Fingernail nitrogen content correlated linearly with muscle nitrogen content in both NG (n = 0.48, P < 0.002) and IGR (n = 0.67, P < 0.005) neonates. The regression equation for the entire study population was: FN = 0.31MN + 9.96, S_yx = ± 0.778, r = 0.59, P < 0.001. These data suggest the possibility of using simple, noninvasive fingernail “biopsies” to monitor protein economy and quality of perinatal growth.

Speculation: In the perinatal period, 90% of muscle nitrogen belongs to proteins, which in turn account for 25% of total body proteins and possibly a larger proportion of mobilizable proteins. Muscle nitrogen content might therefore reflect the status of the body's protein economy and growth. Since fingernail nitrogen content correlates with muscle nitrogen content, fingernails may become a more accessible indicator of underlying metabolic events. Moreover, because of the fingernails' slow rate of growth, their nitrogen content may provide information on metabolic events that occurred several weeks before birth.

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