Intrathecal accumulation and regulation of ascorbate in brain. Ascorbate concentrations in human cerebrospinal fluid and serum

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9thMeetingof the ESN

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HISTAMINE /HA/ UPTAKE AND RELEASE BY ENDOTHELIAL CELLS IN PRIX&RY CULTURES OF EMBRYONIC BRAIN OF RATS. Z. Husztil, F.Jo6* and 1.:.De112 Senunelweis Med. School, Budapest1 and Biol. Centre Hung. A&ad. Sci.,Szegedz

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BLCXID--IAL CELL AND -D-BRAIN POW OF AMINO ACIDS.

TRANS-

JM Lefauconnier, G Bernard INSERMU 26, 200 rue du FaulmurgSaintDenis 75475Paris Cedex 10 - France

Recently, we have showed that labelled HA is taken up by glial cells and released (or metabolized) by sodium/' /potassium-dependent manner. Present studies demonstrates that HA may also be taken up by (and released from) endothelial cells.Incubation of cultured endothelial cells with low concentrations of 3H-HA,resulted in a rapid uptake of the amine. The uptake was moderately Na'-dependent and gave a Km of 0.5 uP1 and a Vmax of 5 pmol x mg protein-l x min-1. After 5 min incubation of the cells (had been exposured to 3H-HA) in a fresh medium;70% of HA, taken up, was released. Potassium accelerated the efflux, while spartein (K+-channel blocker) did not influence the ou+ward flux of HA. The ability of these cells to take up and release HA, appeared as proof for the existence of a system operating as brain-blood barrier.

Three transportsystemshavebeendescribed for blocd-braintransprt of amino acids: the L systemfor neutralaminoacids,a system for basic amino acids and a systemfor acidicamino acids.Gn the ablminal men-brane of endothelialcells exist in additionenergy dependentsystem: A and ASC system for neutral amim acids and a very activesystemfor glutamicacid. The amino acidswhich have no blood-brain transporteitherhave no carrier on the luminalmmbrane or have a carrier but a back-fluxdue to the transportsysyms in the oppxitedirectionon the ablumlnalmu&branepreventtheirblood-braintransport. Wefoundthatsaneaminoacidshavemcarrier butmstof themare transportedinto the endothelialcell. Hmever, the back-flux was very iqortant for thosewhich have a transpzt system in the oppositedirectionon the ablminalmmbram. In immture animls, the carriersare mtwelldeveloped on ti ablminalmfmbrane.This can contributeto explainthe higherblood-braintransportof aminoacids observedin theseanirmls.

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INTRATHECAL ACCUMUIATION AND REGULATION OF ASCORBATE IN BRAIN. ASCOREATE CONCENTRATIONS IN HUMAN CEREBROSPINAL FLUID AND SERUM.

INFLUENCE OF BRAIN BARRIER

SEROTONIN

H S Sharma’J. Y Olssonl, P K H. Reiber, M. Ruff and M. Uhr Neurochemisches Labor, University Gattingen, Germany The mean cerebrospinal fluid (CSF) ascorbate concentration (Vitamin C) from n=65 human controls (161j~Mol/l) was about 4-fdd higher than the mean ascorbate concentration in blood (44,1flMd/I). But the coefficient d variation in CSF (CV=15.7%) was much smaller than the corresponding value in serum @X=36.4%) indicating that the actual CSF ascorbate concentration is independent from actual blood variitions. CSF ascortaate values are constant in various neurological diseases. But serum ascorbate decreases with increasing albumin CSF/serum quotient (QAlb) in cases of a blood CSF n&n: Wlth a 4-fold increased mean QAlb = barrier d y!I” 16.3 10 the mean serum ascorbate concentration was reduced to 28.@&ld/l, CV=31.0% (n=20). Probably due to CSF bulk flow into venous blood the CSF ascorbate contributes to the serum ascorbate concentration signifkantly (about 56% in controls). A mathematfoal fft of the non-linear ratio between CSF ascorbate and serum ascorbate concentrations confirm thls approach. This evaluation was statIstIcally controlled by the simultaneous anafysls of uric add concentrations with reciprocal blood/CSF concentration gradient. Hlgh lntrathecal ascorb&e concentrations in brain cells (> lmMd/l in gllal cells) might be the origin of the lntrathecal regulation of ascorbate concentration.

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Laboratory of Neuropathology’. University of Uppsala. Sweden and Department of Physiologyz, Banaras Hindu University, Varanasi, India Serotonin is a potent vasoactiveneurochemicalin the CNS. Alteration in the metabolism of this amine is known to occur in a wide variety of neurological and psychiatric conditions’. Since the blood-brain barrier (BBB) is a dynamic physiological regulatory barriers, a possibility exist that altered endogenous serotonin level may influence the permeability properties of the BBB. To test

this hypothesis,exogenousserotoninin a level which may occur in pathological conditions was infused in young (age B-9 weeks) (n -15) and adult (age 24-32 weeks) (n -15) rats. The BBB permeability was measured using intravenous Evans blue and ‘3’I-sodium (both tracers bind to endogenous serum albumin)3. Intravascular (10 pg/kg/min. n-5), intracarotid (2 pglkglmin. n=5) and topical (1 pm/ml on exposed pial membrane, n=5) application of the amine increased the permeability of the EBB lo intravascular tracers after 10 min in young animals. This increase in the permeability of the BBB was largely absent in the adult animals. Pretreatment of young animals with a selective serotonin-, receptor antagonist, ketanserin (n=15, IO mgkg, i.p.) 30 min before serotonin infusion, prevented the increased permeability of the BBB in these animals. Our results show that the serotonin has the capacity to increase the permeability of the BBB via soecific serotonin-, receotors. and this effect of the amine is rel’ated to the age of the animals. L

*

1. Essman W (1978) Serotonin in Health and Disease. Vol I-V. Spectrum. New York. 2. Bradbury M W B (1979) The Concept of a Blood-Brain Barrier, Wiley, Chicester 3. Sherma H S, C&on Y. Dey P K (1990) Brain Res 517: 215.223