Comparison of cerebrospinal fluid transport in fetal and adult sheep

We quantified cerebrospinal fluid (CSF) transport (conductance) and CSF out flow resistance in late-gestation fetal and adult sheep using two methods, a constant pressure infusion method and a bolus injection technique into th e lateral ventricles. No significant differences in CSF conductance (fetus 0.013 +/- 0.002, adult 0.014 +/- 0.003 ml . min(-1) . cmH(2)O(-1)) or CSF o utflow resistance (fetus 83.7 +/- 9.8, adult 84.7 +/- 19.7 cmH(2)O . ml(-1) . min) were observed. To confirm CSF transport to plasma in fetal animals, I-125- or I-131-labeled human serum albumin (HSA) was injected into the la teral ventricles. The tracer entered fetal plasma with an average mass tran sport rate of 1.91 +/- 0.47% injected/h (n = 9). In two fetuses, we monitor ed the tracer appearance in plasma and cervical and thoracic duct lymph aft er injection of radioactive HSA into the ventricular CSF. As was the case i n adult animals, fetal tracer concentrations increased in all three compart ments over time, with the highest concentrations measured in lymph collecte d from the cervical lymphatics. These results 1) indicate that global CSF t ransport parameters in the late-gestation fetus and adult sheep are similar and 2) suggest an important role for extracranial lymphatic vessels in CSF transport before birth.