Plasma and cerebrospinal fluid probenecid concentrations as related to accumulation of acidic biogenic amine metabolites in man

The oral administration of probenecid (100 mg/kg/18 h) to depressed patients results in marked increases in the acidic metabolites of biogenic amines in the cerebrospinal fluid (CSF). In contrast to previous reports (where lower dose rates of probenecid were employed) the increases in 5-hydroxyindoleacetic acid and homovanillic acid were independent of plasma or CSF probenecid concentrations. Higher plasma and CSF probenecid concentrations were found in this study. The binding of probenecid to plasma proteins for each patient was also determined to examine the pharmacodynamics of probenecid distribution. The ratio of probenecid in CSF to the calculated free probenecid in plasma was higher (0.4) and more constant than previously noted. At these higher dose levels, probenecid successfully competes with the active transport process for biogenic amine acidic metabolites and also appears to block its own removal from CSF.A preliminary report of this work was presented (Fed. Proc. 32, 696 (1973).     

Cerebrospinal fluid 5-hydroxyindoleacetic acid (5HIAA) and homovanillic acid (HVA) following probenecid in unipolar depressives treated with amitriptyline

Lumbar cerebrospinal fluid 5-HIAA, HVA, and the ratio 5-HIAA/HVA were measured followed probenecid administration in eleven patints with unipolar depression before and during treatment with amitriptyline (AMI). Control values were obtained from a group of inmate volunteers. Prior to treatment CSF 5HIAA formation in the depressives was not different from controls. During treatment with AMI, CSF 5-HIAA formation decreased. One patient with psychotic symptoms prior to AMI and two patients who developed psychotic reactions on AMI showed relatively low CSF 5HIAA formation prior to antidepressant therapy. Compared to controls CSF HVA values were higher in the depressives prior to AMI therapy.     

Absence of effect of para-chlorophenylalanine on 5-hydroxyindoleacetic acid in cerebrospinal fluid in man

The effect of para-chlorophenylalanine (PCPA) on the 5-hydroxy-indoleacetic acid (5-HIAA) content in human cerebrospinal fluid (CSF) has been studied. There was no effect on the CSF-content of 5-HIAA 12, 24 or 48 h after a single dose of PCPA 1 g p.o. Neither was there any effect after 1 g/day during 4 days. The increase of 5-HIAA after administration of probenecid was reduced during treatment with PCPA 1 g/day. This reduction, however, is not due to a diminished production of 5-HIAA by PCPA but probably caused by a pharmacological interaction between probenecid and PCPA since the concentrations of probenecid in CSF were lower during administration of PCPA than without that drug.It is concluded that PCPA in the doses used in this study gives no effects on the CSF-concentrations of 5-HIAA.     

Determinations of 5-hydroxyindoleacetic acid and homovanillic acid in human CSF with monitoring of probenecid levels in CSF and plasma

The accumulation of 5-HIAA and HVA in cerebrospinal fluid (CSF) was studied in eight healthy volunteers after oral administration of probenecid. Simulation indicated that a dose of 4.5 g probenecid should be used to achieve probenecid plasma concentrations between 200 and 400 g/ml. Almost complete inhibition of the active transport of the acidic metabolites was assumed to be obtained at these concentrations. Probenecid 4.5 g was administered in two doses (2.5 g and 2 g), separated by 4 h. Plasma samples were drawn at varying intervals over a period of 46 h and lumbar puncture (LP) was performed at either 14 h or 20 h after the first administration of probenecid. The concentration of probenecid, 5-HIAA and HVA in CSF was estimated and the probenecid-induced accumulation of 5-HIAA and HVA was compared with their baseline values. There were no statistically significant differences (P>0.05) in the accumulation of the monoamine metabolites between the two LP (14 h and 20 h), neither were there any differences in CSF concentrations of probenecid at the time of LP. There were only small differences in probenecid plasma concentrations, although statistically significant. Due to maximum blockade of the active transport system no correlation was observed between the CSF concentration of probenecid and the induced accumulation of 5-HIAA and HVA, respectively. The range of probenecid-induced accumulation for 5-HIAA and HVA in these volunteers was 156–429% and 183–600%, respectively. The suggested monitoring of probenecid plasma levels is proposed as a suitable model to investigate central neuronal activity of dopamine and serotonin in the central nervous system.     

Interindividual variation in the capacity-limited renal glucuronidation of probenecid by humans

A dose of 1,000 mg probenecid was administered orally to 14 human volunteers in order to quantify the maximal rate of formation and excretion of probenecid acyl glucuronide in the urine. Probenecid showed dose-dependent pharmacokinetics. Plasma protein binding of probenecid was high, being somewhat higher in males (90.7±1.4%) than in females (87.9±1.4%; p=0.0019). It was shown that probenecid is metabolized by cytochrome P-450 into at least two phase I metabolites. Each of the metabolites accounted for less than 12% of the dose administered; the main metabolite probenecid acyl glucuronide, representing 42.9±13.2% of the dose, was only present in urine and not in plasma. The renal excretion rate-time profile of probenecid acyl glucuronide showed a plateau value in the presence of an acidic urine pH. This plateau value was maintained for about 10 h at the dose of 1,000 mg. The height of the plateau value depended on the individual and varied between 250 and 800g/min (15–50 mg/h). It was inferred that probenecid acyl glucuronide is formed in the kidney during blood-to-lumen passage through the tubular cells. We conclude that the plateau value in the renal excretion rate of probenecid glucuronide reflects itsV _max of formation.     

5-Hydroxyindole acetic acid and homovanillic acid in cerebrospinal fluid in manic-depressive psychosis and the effect of probenecid treatment

Summary The increased concentrations of 5-hydroxyindole acetic acid and homovanillic acid produced in cerebrospinal fluid by probenecid has been investigated in 15 manic-depressive patients and 21 psychiatric control patients, and has been related to the concentrations of probenecid in the CSF. The pharmacokinetics of probenecid were the same in the manic-depressive patients and the controls, as judged by its concentrations in plasma (bound and free) and CSF after a standard oral dose p.o., and by measurements of half-life and volume of distribution after intravenous injection. — The manic-depressive patients had lower concentrations of 5-HIAA and HVA than controls at similar CSF concentrations of probenecid; this was concluded from results with pairs of patients matched with regard to probenecid in CSF, and from differences between the patients and controls in the slopes of the regression lines for probenecid in CSF against 5-HIAA/HVA. The differences in 5-HIAA/HVA between the diagnostic groups were greater with increasing concentrations of probenecid in CSF; and, with concentrations of probenecid in CSF>1.0 µg/ml, by using the 5HIAA concentrations it was possible to classify the patients correctly into their diagnostic groups in 92% of cases.     

5-Hydroxyindoleacetic acid (5 HIAA) and homovanillic acid (HVA) following probenecid in acute psychotic patients treated with phenothiazines

Lumbar CSF 5 HIAA and HVA were measured following probenecid administration in acute psychotic patients before and during treatment with phenothiazines. Patients with more classical schizophrenic symptoms had higher values for 5 HIAA/HVA than other psychotics, depressives, and inmate volunteers. Prior to treatment CSF 5 HIAA, but not HVA, correlated significantly with several clinical items related to psychotic disorganization. Phenothiazine treatment produced significant increases in CSF HVA which could not be correlated with the dose of antipsychotic or antiparkinson drugs.     

Direct measurement of probenecid and its glucuronide conjugate by means of high pressure liquid chromatography in plasma and urine of humans

Probenecid with its phase-I metabolites, and phase-II glucuronide conjugate can be analysed by a gradient high pressure liquid chromatographic method. Probenecid glucuronide in plasma with pH 7.4 is not stable and declines to 10% of the original value within 6 h (t_1/21 h). Probenecid glucuronide is stable in urine with pH 5.0, moderately unstable at pH 6.0 (t_1/210 h), and unstable at pH 8.0 (t_1/20.5 h). Probenecid glucuronide is stable in water and 0.01 mol/l phosphoric acid in the autosampler of the high pressure liquid chromatograph. The decrease in concentration in water is 5.5% during 9 h and 0% in diluted acid. Probenecid glucuronide and the phase-I metabolites were not detectable in plasma. The main compound in fresh urine is the phase-II conjugate probenecid glucuronide (62% of a 500 mg dose); the phase-I metabolites are present and only a trace of probenecid is present. The percentage of the dose of the phase-I metabolites varies between 5 and 10, while hardly any probenecid is excreted unchanged (0.33%).     

Effect of ECT and imipramine treatment on the concentration of 5-hydroxyindoleacetic acid (5HIAA) and homovanillic acid (HVA) in the cerebrospinal fluid of depressed patients

The influence of probenecid administration on 5HIAA and HVA concentrations in the CSF of depressed patients, was studied before and after treatment with imipramine or ECT.The average increase of the two metabolites in the CSF after probenecid was similar in the untreated depressed patients and in the same patients improved after both imipramine or ECT treatment.The treatment determined a significant increase in the CSF concentration of the acid metabolites also before the probenecid administration.     

The effect of l-tryptophan administration on the concentration of probenecid in plasma and cerebrospinal fluid in patients

The administration of large doses of probenecid has been used to study the central nervous system metabolism of catecholamines and indoleamines in patients with affective disease. It has been reported that alterations of the binding of l-tryptophan to plasma albumin binding sites occur during probenecid administration. The present study sought to determine if the administration of large doses of l-tryptophan affected probenecid concentrations in cerebrospinal fluid and/or plasma. The data indicate that during l-tryptophan treatment, plasma probenecid concentrations are reduced but that no significant alterations in cerebrospinal fluid probenecid concentrations occur. This would suggest that the kinetics of the probenecid blockade of transport of acidic biogenic amine metabolites out of cerebrospinal fluid are not altered by l-tryptophan loading.     

Probenecid: Dosage,levels in plasma and cerebrospinal fluid (CSF) and influence upon CSF levels of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in the rabbit

Probenecid retards the efflux of acid monoamine metabolites from the brain tissue and CSF to the blood. The probenecid-induced accumulation of these metabolites is held to be indicative of the turnover rate of the corresponding amines. Although the penetration of probenecid into the CSF does not proceed at a constant rate, Korf et al. (1972) and Sjöstrom (1972) have shown a correlation between CSF levels of probenecid and that of HVA and 5-HIAA. In this study an attempt was made to establish the relationship between doses of probenecid and levels of this compound in plasma and CSF; between levels in plasma and CSF; and between CSF levels of probenecid and of HVA and 5-HIAA. This study was performed in a homogeneous group of laboratory rabbits.All correlations proved to be significant. The implications of these results for studies using the probenecid technique are discussed.     

Probenecid in CSF and plasma of rabbits and dogs measured by radioimmunoassay

Probenecid (P) in CSF of rabbits and dogs was investigated using a new radioimmunoassay technique. In rabbits, under steady-state conditions, CSF/free plasma concentration ratios of P were found to be similar to those reported in man. The ratios were concentration dependent and less than 0.5 suggesting an inhibition of transport of the drug in CNS. Under nonsteady-state conditions, no clear evidence of a transport system was found in dogs.     

反相HPLC法测定人血浆中5-氟尿嘧啶的浓度

目的：建立RP-HPLC法测定人血浆中5-氟尿嘧啶的浓度。方法采用Agilent Eclipse XDB-C18色谱柱,流动相为0.02mol· L -1的磷酸二氢钾缓冲溶液（pH＝3.0）,流速为1.0mL· min -1,检测波长为264nm,柱温为25℃。结果5-氟尿嘧啶在2.0～30.0μg· mL -1度范围内呈良好的线性关系,检测限为4.0ng。5-氟尿嘧啶浓度为2.0、10.0、20.0μg· mL -1的日内RSD分别为3.6％、2.2％、1.1％,日间 RSD分别为5.2％、3.4％、1.8％,平均回收率分别为105.3％、97.2％、98.6％。结论该方法简便、快速、准确、重现性好,适用于5-氟尿嘧啶的药代动力学研究及临床血药浓度检测。     

Dose-dependent pharmacokinetics of probenecid in the rat

The basic pharmacokinetics of probenecid was studied by administration of three different i.v. bolus doses (50, 75, and 100 mg kg-1) to rats. The protein binding of probenecid in pooled rat serum was estimated by equilibrium dialysis. The unbound fraction was found to increase non-linearly with increasing total concentration, yielding a maximum free fraction of 49 per cent. The plasma concentration data obtained were described by a two-compartment model with Michaelis-Menten elimination. The maximal rate of elimination (Vm) remained unchanged between different doses irrespective of whether it was calculated in total or free concentrations (mean 187.2 +/- 8.3 (SD) microgram min-1). The Michaelis-Menten constant (Km) decreased slightly with increasing dose, while the unbound Michaelis-Menten constant (Km,u) did not change between the doses (mean 37.1 +/- 1.3 (SD) microgram ml-1). The volume of distribution of the central compartment (Vc) did not alter when the dose was increased from 50 to 100 mg kg-1 (mean 56.5 +/- 4.3 (SD) ml), but the unbound volume of distribution of the central compartment (Vc,u) decreased from 186.5 +/- 15.6 (SD) to 89.8 +/- 6.9 (SD) ml, which is in accordance with the reduction to be expected for drugs that only distribute in the extracellular fluid.     

A pilot study of the predictive value of the probenecid test in application of 5-hydroxytryptophan as antidepressant

In depressions, varying therapeutic effects have been obtained with 5-HT precursors. This is possibly due to the fact that the group of the depressions is pathogenetically heterogeneous; that, specifically, some types do and other types do not entail disturbances in the central 5-HT metabolism; and that only the former types are precursor-sensitive. This hypothesis was tested in a preliminary pilot study, and confirmed. The central 5-HT consumption was assessed on the basis of the probenecid test. In this experiment, 5-HTP was for the first time given in large doses over a considerable period of time.This study was supported by grants from the Netherlands Organization for Pure Research (Z.W.O.), the Preventie Fonds and the Merck Sharp & Dohme Research Laboratories (U.S.A.).     

Influence of probenecid and paracetamol (acetaminophen) on zidovudine glucuronidation in human liver in vitro.

The effects of probenecid and paracetamol on zidovudine glucuronidation were investigated, in vitro, using human liver microsomal preparations. The presence of probenecid in the incubation medium significantly reduced the maximum reaction velocity for zidovudine glucuronide formation by more than 60 per cent, and the Km was reduced by 47 per cent, suggesting an uncompetitive inhibition of zidovudine glucuronidation. In contrast, paracetamol had no significant effect on zidovudine glucuronidation. The maximum reaction velocity for zidovudine glucuronide formation and the Km were unchanged when paracetamol (5 mM) was present in the incubation medium. The effects of probenecid and paracetamol on zidovudine metabolism in vitro correlates closely with those observed in vivo. The in vitro system of human liver microsomes may have a useful role in predicting the possible interaction of other drugs with zidovudine metabolism.     

Acute tryptophan depletion attenuates the prolactin response to d-fenfluramine challenge in healthy human subjects

Prolactin responses to d-fenfluramine (d-FEN) Challenge (0.5 mg/kg PO) were examined after pretreatment with and without acute tryptophan depletion (ATD) in six physically healthy male volunteers. Compared to pretreatment with SHAM-ATD, ATD pretreatment attenuated the PRL response to d-FEN Challenge in all subjects. These data suggest that PRL responses to d-FEN challenge reflect to a substantial degree the activity of newly synthesized 5-HT. Received: 12 June 1997 /Final version: 19 December 1997     

Assessment of cerebrospinal fluid levels of dopamine metabolites by gas chromatography

The acid metabolites of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were determined in lumbar cerebrospinal fluid (CSF) by a new procedure. After gas Chromatographic separation, the pentafluoropropionyl 2,2,3,3,3-pentafluoro-1-propionyl esters of DOPAC and HVA were analyzed by electron capture detection. Normal HVA levels were quantitated in as little as 0.1 ml CSF. No significant amounts of DOPAC (< 1 ng/ml) were found in any of the drug-free samples analyzed. Levels of DOPAC increased only marginally in the CSF of patients receiving acute or chronic doses of lDopa. Baseline HVA levels ranged from 4.5–50 ng/ml with a mean value of 23 ng/ml. These studies demonstrate that HVA is the major dopamine metabolite in human CSF.Supported by a grant from the NIMH No. MH 21638-03 and a Research career development award No. 1 K04 GM 40793-05 to S. W.     

复方氨苄西林分散片中二组分含量的HPLC测定

目的建立高效液相色谱法测定复方氨苄西林分散片中氨苄西林与丙磺舒含量的方法。方法采用十八烷基硅烷键合硅胶为色谱柱,流动相为磷酸盐缓冲液(含0.05 mol.L-1磷酸二氢钾,0.01 mol.L-1十二烷基硫酸钠,1%醋酸和0.4%三乙胺,以磷酸调pH值至3.0)-甲醇(50∶50),检测波长为235 nm。结果氨苄西林和丙磺舒分别在0.1～2.0 mg.mL-1(r=0.999 2)和0.028～0.56 mg.mL-1(r=0.999 9)浓度范围内线性关系良好,平均回收率分别为101.2%和99.1%。结论本法简便、准确,重复性好。     

Biochemical aspects of tryptophan depletion in primates

We studied the degree of plasma tryptophan depletion produced by giving normal human males different amounts of a tryptophan-free (T-) amino acid mixture. From the results of this and other studies we concluded that the maximum degree of tryptophan depletion can be produced by a 31.5 g mixture of seven essential amino acids. Administration of a T–amino acid mixture to vervet monkeys lowered tryptophan and 5-hydroxyindoleacetic acid in the cerebrospinal fluid. Levels of tyrosine and the catecholamine metabolites were unchanged. These data support the idea that the effects of T–mixture on mental function in humans which have been reported previously are due to a decrease in 5-hydroxytryptamine.