Dilution Kinetics of Chemicals Used for Estimation of Water Content of Body Compartments in Perinatal Medicine

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Abstract
Dilution kinetics of markers commonly used for estimation of body water content and distribution in perinatal medicine (p-aminohippurate, inulin, antipyrine, H2'8O, bromide, and T1824) were studied in pregnant and neonatal baboons. Amniotic fluid concentrations of p-aminohippurate and inulin decreased exponentially after intraamniotic injection of these markers; from 2-24 h after injection, concentrations decreased linearly on semilogarithmic plot (r=0.96-1.00). Plasma concentrations of antipyrine decreased exponentially during the first 60 min after intravenous injection, then linearly from 1-5 h (r=0.92-0.90). Plasma concentrations of I8O decreased linearly from 1-6 h after injection in three or four cases (r=0.94-0.99). Plasma concentrations of bromide decreased during the first 2 h after injection, then stabilized for at least 3 h. Plasma concentrations of T1824 decreased linearly from 10-60 min after intravenous injection (r=0.97- 1.00). Then the decline became exponential until 5 h. These data allow us to make specific recommendations regarding the optimal time and method of amniotic fluid and blood sampling during body water studies.