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(Stroke. 1974;5:81.)
© 1974 American Heart Association, Inc.

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Stereospecific Permeability of Rat Blood-Brain Barrier to Lactic Acid

EDWIN M. NEMATO PH.D.¹ JOHN W. SEVERINGHAUS M.D.²

¹ Department of Anesthesiology, University of Pittsburgh, 1081 Scaife Hall, Pittsburgh. Pennsylvania 15261
² Cardiovascular Research Institute, University of California, San Francisco Medical Center, San Francisco, California 94122

Blood and whole brain ¹⁴C and ³²P activities were determined in hepatectomized rats one, two, five and ten minutes after intravenous (I.V.) injection of ¹⁴C-labeled L-lactate or D-lactate and ³²P-labeled rat red blood cells. Whole brain homogenate ¹⁴C was corrected for blood ¹⁴C and chemically partitioned into ¹⁴C-lactate, ¹⁴CO₂ and other ¹⁴C compounds. In controls, lactate was replaced with ¹⁴C-D-glucose and ¹²⁵l-antipyrine. At one minute postinjection, whole brain ¹⁴C expressed as percent of total injected ¹⁴C activity and as percent of the antipyrine value were: antipyrine 1.78% (100%); D-glucose 1.45% (81%); L-lactate 0.36% (20%); and D-lactate 0.13% (7%). One minute after L-lactate injection, brain ¹⁴C was 74% lactate, 5% CO₂ and 21% other compounds. Preloading rats with cold racemic Na-lactate reduced L-lactate uptake to 0.14% of the injectate (8% of antipyrine), and reduced D-Iactate uptake to 0.09% (= 5% of antipyrine). At two, five and ten minutes, brain contained more ¹⁴C with larger fractions metabolized to CO₂ and other compounds from both L-lactate and D-lactate. The blood-brain barrier appears to contain a saturable lactate carrier exhibiting threefold L-stereospecificity to D-stereospecificity, but resulting in far less net transport than the comparable glucose carrier. Lactate transport may be limited by the scarcity of neutral lactic acid at normal blood pH.

Key Words: locate permeability • brain locate uptake • carrier transport • facilitated transport • saturable transport

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