The missing link in amniotic fluid volume regulation: intramembranous absorption

Article Abstract:

Amniotic fluid, the fluid surrounding the fetus during pregnancy, is usually maintained within a normal range throughout pregnancy. The amount of fluid swallowed by the fetus is less than the amount of fluid excreted in the fetal urine. Therefore, another mechanism is involved in regulating amniotic fluid balance. Pregnant sheep were studied to see if fluid is transferred to the amniotic fluid as the fetal blood passes through the fetal membrane and placenta (organ of fetal nutrition). Warmed distilled water was injected into the amniotic fluid of three groups of sheep. Fetuses in one group had their esophagi blocked, in another the esophagus remained intact, and in the third group, the fetuses were sacrificed before the experiment began. The concentration of salt was measured in the fetus and the mother to determine the dilution factor after the fluid was injected into the amniotic fluid. In normal fetuses the salt concentration decreased, the heart rate increased and blood pressure increased. This indicated that the injected fluid rapidly entered the fetal blood circulation. At the same time, the salt concentration of the mother decreased. In the fetuses killed before the experiment began, the mother's salt concentration remained unchanged. There was no difference between the group of fetuses with intact or blocked esophagi, except that in the fetuses with a blocked esophagus, the concentration of salt fell more rapidly. Therefore, the intramembranous pathway, the absorption of water into the fetal blood that flows through the fetal membranes and placenta, plays a major role in the maintenance of amniotic fluid. (Consumer Summary produced by Reliance Medical Information, Inc.)

Models, Laws, regulations and rules, Measurement, Maternal-fetal exchange, Physiological aspects, Fluid-electrolyte balance, Osmoregulation, Body fluids

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Potential route for fetal therapy: intramembranous absorption of intramniotically injected furosemide

Article Abstract:

The drug furosemide may be administered directly into the amniotic cavity to be absorbed by the fetus, thus reducing side effects to the mother. Furosemide is given to pregnant women with a lack of amniotic fluid to induce the fetus to urinate and increase fluid in the amniotic sac. When given via the mother, however, furosemide can cause the mother to urinate, reducing her total body fluids. Researchers tested nine sheep fetuses, and found that they experienced a quick and lasting increase in urination in response to furosemide injected directly into the amniotic cavity, but their mothers did not. Four fetuses had had their esophagus tied off, yet they still absorbed enough furosemide through the placental membranes to increase their urine output.

Drugs, Fetus, Drug therapy, Dosage and administration, Drug administration and dosage, Furosemide

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Technetium Tc 99m rapidly crosses the ovine placenta and intramembranous pathway

Article Abstract:

Technetium Tc 99m may be directly absorbed from and transported into the amniotic cavity in sheep. Amniotic fluid mostly comes from fetal urination, but urine contains lower ion concentrations. Researchers tracked ion transport into and out of amniotic fluid by injecting technetium Tc 99m, a radioactive ion, into a fetal vein, the amniotic cavity, or a maternal vein in sheep. The ion moved readily across the placenta in both directions. This suggests that ion transport across fetal membranes helps maintain ion concentrations in amniotic fluid. However, sheep have blood vessels in the fetal membranes and humans do not.

Analysis, Biological transport

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