Steady-state placenta

Gromer S Arscott, LD WCH, Jr SRH, Becker K (1998) Human placenta thioredoxin reductase. Isolation of the selenoenzyme, steady state kinetics, and inhibition by therapeutic gold compounds. J Biol Chem 273 20096-20101... 

The apparent volume of distribution of ciprofloxacin is 2-3.5 L/kg, and the apparent volume of distribution at steady state is 1.7-2.7 L/kg. Only low concentrations of ciprofloxacin are distributed into cerebrospinal fluid (CSF). Peak CSF concentrations may be 6-10% of peak serum concentrations. The drug is moderately bound to serum protein (16-43%), and crosses the placenta and is produced with the mammary milk [6, 10],... 

Following a 10-minute inhalation exposure to 2,000 ppm of benzene by pregnant mice, benzene and its metabolites were found to be present in lipid-rich tissues, such as brain and fat, and in well-perfused tissues, such as liver and kidney. Benzene was also found in the placenta and fetuses immediately following inhalation of benzene (Ghantous and Danielsson 1986). During inhalation exposure of rats to 500 ppm, benzene levels reached a steady-state concentration within 4 hours in blood (11.5 pg/mL),... 

Distributed parameter, nonlinear, partial differential equations were soloed to describe oxygen transport from maternal to fetal bloody which flows in microscopic channels within the human placenta. Steady-state solutions were obtained to show the effects of variations in several physiologically important parameters. Results reported previously indicate that maternal contractions during labor are accompanied by a partially reduced or a possible total occlusion of maternal blood flow rate in some or all portions of the placenta. Using the mathematical modely an unsteady-state study analyzed the effect of a time-dependent maternal blood flow rate on placental oxygen transport during labor. Parameter studies included severity of contractions and periodicity of flow. The effects of axial diffusion on placental transport under the conditions of reduced maternal blood flow were investigated. 

If the above requirements are met, then the placenta is placed in the artificial uterus and perfusion by heparinized buffered solution (Appendix IA) is started as soon as possible to prevent clotting of the blood already present in the small capillaries. After the placenta is cleaned by perfusing with saline and the intactness of the placental membrane has been established, the blood perfusion is started. When the system has reached steady state (with regard to pressures, temperature, etc.) at physiological conditions, data are collected. 

Sampling. For steady-state experiments, glucose was added continuously to the maternal reservoir. The placenta was weighed before being placed in the artificial uterus, the rate of utilization of glucose by the placenta was then estimated, and the rate of glucose added was set approximately to the estimated rate of utilization. 

The net rate of glucose metabolism by the placenta may also be affected by the rate at which glucose is being transferred. Under steady-state conditions, there was no net transfer of glucose because no glucose... 

Ropivacaine is 94% bound to alpha-1 glycoprotein and is mainly protein-bound. After intravascular infusion, steady-state volume of distribution is 41 ht-ers. In addition, ropivacaine readily crosses the placenta and unbound concentration equilibrium is quickly reached. The degree of plasma protein binding in the fetus is less than in the mother. This results in lower total plasma concentrations in the fetus than in the mother. The ratios of umbilical vein to maternal vein total and free concentrations are 0.31 and 0.74, respectively. 

A Detailed Quantitative Analysis of O2 Transport in the Human Placenta during Steady- and Unsteady-State Conditions... 

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