engleski

Transventricular and transpial absorption of cerebrospinal fluid into cerebral microvessels

Absorbtion of cerebrospinal fluid (CSF) volume is generally assumed to take place across arachnoid villi into venous sinuses or via perineural sheats of cranial nerves into lymphatics. However, in previous studies various macromolecules (proteins, dextrans, inulin) were used as markers of CSF volume absorption and infused into CSF under increased pressure what could damage integrity of arachnoid membrane. Since 99% of CSF is water, we assume that labelled water (3H-water) should be used to study absorption of CSF volume and applied into CSF under normal pressure. In acute experiments in cats lateral brain ventricle was cannulated and either solution of 3H-water or 3H-inulin were slowly infused (1.77 µ l/min) over 3 hours and their concentrations measured in cisternal CSF, arterial plasma and venous plasma from confluence of sinuses which is drained from periventricular capillaries. In subchronic experiments the cannula was implanted and fixed in lateral ventricle and connected to osmoatic minipump (model 1701, Alzet Corp.) which delivered either 3H-water or 3H-inulin at rate 1 µ l/h for 5 days in free moving cats. At the end of experiments samples of arterial and confluence plasma and CSF from cisternal, cortical, thoracic and lumbar region were taken for analysis. In acute experiments concentration of 3H-water in confluence plasma was much higher than concentrations in cisternal CSF and arterial plasma which were equal. After intravenous bolus injection of 3H-water its concentrations in arterial plasma and cisternal CSF equilibrated in 5 min. When 3H-inulin was infused intraventricularly its concentration was high in cisternal CSF and very low in arterial and confluence plasma. In subchronic experiments concentrations of 3H-water was equal in confluence and arterial plasma and in various compartments of CSF, while concentrations of 3H-inulin was much lower in arterial and confluence plasma than in various compartments of CSF where concentrations were equal. These data indicate that 3H-water is absorbed transventricularly into periventricular capillaries and reaches high concentration in confluence plasma and is then diluted in systemic blood to quickly equilibrate with CSF but it is not carried from lateral ventricle to cisterna magna. On the contrary 3H-inulin, macromolecule known to pass poorly capillary walls, is carried by to-and-fro pulsation and mixing of CSF along CSF spaces and slowly eliminated. These conclusions are supported by our experiments with infusion of 3H-water or 3H-inulin into cortical CSF showing transpial absorption of 3H-water into adjacent capillaries. Since cerebral capillaries surface area is enormous in comparison to surface of arachnoid villi or perineural sheats, our results suggest that volume of CSF (water) is absorbed into cerebral microvessels.

absorption ; CSF ; cerebral microvessels

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