title: Effect of capillary efflux transport inhibition on the determination of probe recovery during in vivo microdialysis in the brain.
abstract: Intracerebral microdialysis probe recovery (extraction fraction) may be influenced by several mass transport processes in the brain, including efflux and uptake exchange between brain and blood. Therefore, changes in probe recovery under various experimental conditions can be useful to characterize fundamental drug transport processes. Accordingly, the effect of inhibiting transport on probe recovery was investigated for two capillary efflux transporters with potentially different membrane localization and transport mechanisms, P-glycoprotein and an organic anion transporter. Fluorescein/probenecid and quinidine/LY-335979 were chosen as the substrate/inhibitor combinations for organic anion transport and P-glycoprotein-medicated transport, respectively. Probenecid decreased the probe recovery of fluorescein in frontal cortex, from 0.21 +/- 0.017 to 0.17 +/- 0.020 (p < 0.01). Quantitative microdialysis calculations indicated that probenecid treatment reduced the total brain elimination rate constant by 3-fold from 0.37 to 0.12 (ml/min. ml of extracellular fluid). In contrast, the microdialysis recovery of quinidine, delivered locally to the brain via the probe perfusate, was not sensitive to P-glycoprotein inhibition by systemically administered LY-335979, a potent and specific inhibitor of P-glycoprotein. Recovery of difluorofluorescein, an analog of fluorescein, was also decreased by probenecid in the frontal cortex but not in the ventricle cerebrospinal fluid. These experimental observations are in qualitative agreement with microdialysis theory incorporating mathematical models of transporter kinetics. These studies suggest that only in certain circumstances will efflux inhibition at the blood-brain barrier and blood-cerebrospinal fluid barrier influence the microdialysis probe recovery, and this may depend upon the substrate and inhibitor examined and their routes of administration, the localization and mechanism of the membrane transporter, as well as the microenvironment surrounding the probe.
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, Omaha, Nebraska, USA.
authors.forename: H
authors.initials: H
authors.lastname: Sun
authors.forename: P M
authors.initials: PM
authors.lastname: Bungay
authors.forename: W F
authors.initials: WF
authors.lastname: Elmquist
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors; D000818:Animals; D027321:Anion Transport Proteins; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D001812:Blood-Brain Barrier / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000378:metabolism*; D002199:Capillary Permeability / Q000187:drug effects / Q000502:physiology*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors; D018592:Cross-Over Studies; D003986:Dibenzocycloheptenes / Q000494:pharmacology; D005452:Fluoresceins / Q000032:analysis / Q000493:pharmacokinetics; D005456:Fluorescent Dyes / Q000032:analysis / Q000493:pharmacokinetics*; D005625:Frontal Lobe / Q000378:metabolism; D008297:Male; D017551:Microdialysis / Q000379:methods*; D008954:Models, Biological; D011339:Probenecid / Q000494:pharmacology; D011802:Quinidine / Q000032:analysis / Q000493:pharmacokinetics; D011804:Quinolines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D027321:Anion Transport Proteins; D002352:Carrier Proteins; D003986:Dibenzocycloheptenes; D005452:Fluoresceins; D005456:Fluorescent Dyes; D011804:Quinolines; C095179:zosuquidar trihydrochloride; D011802:Quinidine; D011339:Probenecid