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At least 487 records · Page 27Linked to original sources
PubMed1994

Contribution of probenecid-sensitive anion transport processes at the brain capillary endothelium and choroid plexus to the efficient efflux of valproic acid from the central nervous system.

The steady-state brain-to-free plasma concentration ratio of valproic acid (VPA) is well below unity, which suggests that it is efficiently removed from the central nervous system (CNS) by specialized transport processes. The purpose of this study was to determine whether probenecid (PBD)-sensitive anion transporters at the choroidal epithelium and brain capillary endothelium are involved in the clearance of VPA from the CNS of the rabbit. Unlabeled VPA was infused i.v. to achieve a steady-state plasma concentration while a tracer concentration of 3H-VPA was introduced into the ventricles by ventriculocisternal (VC) perfusion. In two treatment groups, PBD was administered by direct placement into the VC perfusate or by a combination of an i.v. priming dose and continuous infusion. In the control group, no other treatments were given. PBD administered by either route had no effect on the steady-state VC extraction of 3H-VPA (approximately 57%). Coadministration of PBD through the VC perfusate had no apparent effect on the blood-brain distribution of unlabeled VPA. In the i.v. PBD group, the concentration in the brain of systemically administered VPA increased 1.5- to 2-fold in all regions compared with that in control animals. Because neither the total nor the free plasma concentration of VPA was affected by PBD, the increase in brain VPA concentration reflected a blockade of VPA efflux across the brain capillary endothelium. These results suggest that PBD-sensitive transport at the brain capillary endothelium is the main route of VPA efflux from the CNS.

Animals↗
PubMed1993

Distributional transport kinetics of zidovudine between plasma and brain extracellular fluid/cerebrospinal fluid in the rabbit: investigation of the inhibitory effect of probenecid utilizing microdialysis.

The effect of probenecid (PBD) on the distributional transport of zidovudine (AZT) between plasma, cerebrospinal fluid (CSF) and brain extracellular fluid (ECF) was investigated by using microdialysis. New Zealand White rabbits received AZT, in a crossover design, during control and treatment periods. PBD was coadministered at one of two rates. One additional study involved a repeated control to investigate the possible existence of a period effect. In the low- and high-dose treatment groups, PBD decreased the total body clearance of AZT by 47.7 +/- 8.9 and 51.7 +/- 9.7%, respectively. PBD also decreased the clearance of AZT from CSF and thalamus ECF, prolonging the half-lives of AZT disappearance from the brain. Additionally, PBD elevated the AZT area under the concentration-time curve in the ventricular CSF 3- to 5-fold and the area under the thalamic ECF concentration-time curve by 5- to 6-fold, whereas the area under the plasma concentration-time curve increased only 2-fold. During PBD treatment the ratio area under the thalamic ECF concentration-time curve/area under the ventricular CSF concentration-time curve approached unity. These results provide evidence that AZT is actively transported outwardly across the CSF- and brain ECF-blood barriers, and this transport system is sensitive to PBD. A pharmacokinetic model that considers the effect of PBD on the AZT clearance from brain to plasma suggests that 73% of this pathway is subject to competitive inhibition by PBD.

Animals↗
PubMed1997

In vitro mechanisms of probenecid-associated alterations in acetaminophen glucuronide hepatic disposition.

The effect of probenecid (PRB) on factors regulating the hepatic disposition of acetaminophen glucuronide (AG) was investigated in vitro. Potential interactions in metabolism or binding to cytosolic proteins were examined. In the absence of PRB, AG formation in rat hepatic S9 fractions was saturable (V(max) = 2.77 +/- 0.36 nmol/ min/mg protein; K(M) = 18.0 +/- 0.92 mM). PRB significantly decreased V(max), but not K(M), for AG formation, consistent with noncompetitive inhibition. Various models were fit to the AG formation rate vs. acetaminophen (APAP) and PRB concentration data to elucidate the mechanism of inhibition by PRB. A partial noncompetitive inhibition model (K(i) = 1.10 +/- 0.01 mM) described the data best based on model selection criteria. AG did not bind to the cytosolic protein ligandin (glutathione S-transferase A1). These data indicate that PRB is a potent partial noncompetitive inhibitor of acetaminophen glucuronidation in vitro. PRB-associated alterations in AG hepatic disposition in vivo are not due to altered binding of AG to GSTA1 but may be attributed in part to impaired AG formation.

Acetaminophen↗
PubMed1997

Effects of probenecid on brain-cerebrospinal fluid-blood distribution kinetics of E-Delta 2-valproic acid in rabbits.

E-Delta 2-valproic acid (E-Delta 2-VPA), a major active metabolite of VPA, has been proposed as an alternative to VPA because it is less hepatotoxic and is nonteratogenic. In rodents, VPA and E-Delta 2-VPA have a brain tissue/free plasma concentration ratio less than unity, which suggests rapid removal of the alkanoate anticonvulsants from the central nervous system. This study in rabbits employed a simultaneous iv infusion-ventriculocisternal (VC) perfusion technique to investigate the steady-state kinetics of E-Delta 2-VPA transport at the blood-brain barrier, the blood-cerebrospinal fluid (CSF) barrier, and the neural cell membrane. Probenecid (PBD) was coadministered to probe the mediation of transport by organic anion transporter(s). Rabbits in the control group (N = 6) received an iv infusion of E-Delta 2-VPA to achieve a steady-state plasma concentration of 50 to 60 microg/ml. Blood and cisternal outflow of mock CSF perfusate were continuously sampled. Midway through the experiment, the VC perfusate was switched to one containing [3H]E-Delta 2-VPA. At 225 min, the rabbits were sacrificed, and each brain was removed and dissected into ten regions. Rabbits in the PBD group (N = 9) received an iv infusion and VC perfusion as in the control group as well as concomitant iv infusion of the inhibitor. The mean steady-state VC extraction ratio for [3H]E-Delta 2-VPA did not differ between the control and PBD groups (63.7 +/- 8.3% vs. 60. 6 +/- 9.6%), indicating the lack of a significant PBD-sensitive transport at the choroidal epithelium. Coadministration of PBD elevated brain concentration of cold E-Delta 2-VPA in the absence of a significant change in total or free steady-state plasma concentration. Mean E-Delta 2-VPA brain tissue/free plasma concentration ratios in the various brain regions were 3.5- to 5.2-fold higher in PBD-treated animals than in the controls. Significant increases (3.0- to 4.5-fold) in the mean brain tissue/cisternal perfusate concentration ratios were also observed. Compartmental modeling of the steady-state distribution data suggested that clearance of E-Delta 2-VPA from the brain parenchyma is governed jointly by efflux transporters at the neural cell membrane and brain capillary endothelium. Moreover, PBD-induced elevation of E-Delta 2-VPA tissue concentrations is attributed primarily to inhibition of E-Delta 2-VPA efflux transport at the neural cell membrane, resulting in both intracellular trapping and greater tissue retention of E-Delta 2-VPA.

Animals↗
PubMed1998

Restoration of the uricosuric effect of probenecid after triglycylvasopressine administration in a gouty patient.

A 35-year-old patient with severe gout and mild renal insufficiency presented very low urinary urate excretion. Volume expansion induced by fludrocortisone combined or not with a uricosuric drug (Benzbromarone) was unable to significantly increase his urate excretion. A combined Probenecid (PB) and Pyrazinamide (PZA) test was performed. These drugs being considered to affect renal tubular reabsorption or secretion. No significant modification of uric acid fractional excretion (FE.uric acid) was observed after PB and PZA. When the same test was performed after the administration of Triglycyl-lysine vasopressine (TGLV), a potent V1 receptor stimulator, we observed a three fold increase in FE.uric acid after PB intake (from 6 to 18%) followed by a decrease after PZA (from 18 to 5.6%). When TGLV was administered alone their was no significant modification of uric acid fractional excretion. We propose that TGLV decrease proximal tubular urate reabsorption that could only be detected when postsecretory reabsorption is blocked by an uricosuric drug.

Absorption↗