Abstract
This study was performed to evaluate quantitatively the brain distribution and the efflux transport across the blood-brain barrier of probenecid, using in vivo microdialysis and in situ brain perfusion techniques. The brain interstitial fluid (ISF)-to-plasma cerebrospinal fluid (CSF)-to-plasma and brain tissue-to-plasma unbound concentration ratios of probenecid at steady state were less than unity, which suggests restricted distribution in the brain. An uphill concentration gradient from ISF to plasma and a downhill concentration gradient from CSF to ISF were observed. Kinetic analysis revealed that the efflux clearance from brain ISF to plasma (0.0373 ml/min/g brain) was significantly greater than the influx clearance from plasma to brain (0.00733 ml/min/g brain). The ratio of the ISF concentration (Cisf) to the plasma unbound concentration (Cp,f) of probenecid was increased 2- to 3-fold by salicylate (3.7 mM) and benzoate (3.6 mM), which are accepted as substrates of the monocarboxylic acid transport system, compared with the same ratio for the control. In addition, the ratio Cisf/Cp,f was increased by treatment with N-ethylmaleimide, a sulfhydryl-modifying agent, whereasp-aminohippuric acid and choline did not produce increasing effects on Cisf/Cp,f. These data suggest that the restricted distribution of probenecid in the brain may be ascribed to efficient efflux from the brain ISF, which may be regulated by the monocarboxylic acid transport system at a relatively high ISF concentration.
Footnotes
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Send reprint requests to: Ryohei Kimura, Ph.D., Professor, Department of Biopharmacy, School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Shizuoka 422, Japan.
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↵1 This study was supported in part by a Grant-in-Aid for Scientific Research provided by the Ministry of Education, Science and Culture of Japan.
- Abbreviations:
- Am
- total amount taken up by the brain
- BBB
- blood-brain barrier
- BCECs
- brain capillary endothelial cells
- BCSFB
- blood-cerebrospinal fluid barrier
- BSA
- bovine serum albumin
- Cd,inlet
- infusion dose given into the brain interstitial fluid
- Cisf
- concentration in interstitial fluid
- Cp,f
- unbound concentration in plasma
- Cperfusate
- concentration in perfusate
- CLcsf
- cerebrospinal fluid clearance
- CLin
- influx clearance from plasma to brain
- CLout
- efflux clearance from brain to plasma
- CSF
- cerebrospinal fluid
- fp
- unbound fraction in plasma
- ISF
- interstitial fluid
- Keff
- efflux rate constant from brain to plasma
- Ki
- inhibition constant
- Km
- Michaelis constant
- KRP buffer
- Krebs-Ringer phosphate buffer
- MeAIB
- methylaminoisobutyric acid
- MCT
- monocarboxylic acid transport
- NEM
- N-ethylmaleimide
- NMN
- N′-methylnicotinamide
- PAvitro
- in vitro permeability rate constant of the microdialysis probe
- PAvivo
- in vivo permeability rate constant of the microdialysis probe
- Rvitro
- in vitro recovery of the microdialysis probe
- T½,β
- elimination half life in β-phase
- Tα
- volume of distribution in the brain
- Received May 31, 1996.
- Accepted October 18, 1996.
- The American Society for Pharmacology and Experimental Therapeutics
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