Correlation between brain tissue and cerebrospinal fluid concentrations of selected compounds in rats with intact and injured blood-brain barrier

Local Blood-Brain Barrier Penetration following Systemic Contrast Medium Administration

The present study was initiated by a severe complication in a patient with renal dysfunction who developed cortical blindness and weakness of her left extremities 30 hours following renal and abdominal angiography. To evaluate the impact of prolonged high serum concentrations of contrast medium (CM) this clinical situation was simulated in a laboratory model using sheep with elevated serum levels of contrast medium maintained for 48 hours. The experimental data did not support the theory that the prolonged exposure to high circulating levels of contrast medium (4 ml/kg body weight of meglumine diatrizoate 60%) is sufficient alone to cause penetration of the blood-brain barrier.

Modeling the enhanced uptake of zidovudine (AZT) into cerebrospinal fluid. 1. Effect of probenecid

The kinetics of zidovudine (AZT) distribution into rabbit cerebrospinal fluid (CSF) were studied during continuous infusion of AZT and after iv bolus administration. The CSF/plasma steady-state AZT concentration ratio was 0.192 +/- 0.003. That this ratio is less than unity, and the clearance from the CSF due to bulk flow is much smaller than the total CSF-to-plasma clearance, suggests active CSF-to-plasma transport of AZT. Probenecid coadministration significantly enhances AZT distribution into CSF when plasma and CSF concentrations of AZT are at steady state during continuous infusion of AZT or at a transient steady state after a single iv bolus dose administration. A linear pharmacokinetic model which describes the distribution of AZT into CSF and relates intercompartmental clearances between CSF and plasma was developed and was used to analyze the results. This analysis showed that probenecid enhances the distribution of AZT into the CSF by its effect on clearances between plasma and CSF. The CSF exit-rate constant for AZT estimated during probenecid coadministration was significantly different from controls. Probenecid coadministration resulted in a 36% reduction in the CSF-to-plasma transfer-rate constant. Reduction in the CSF to plasma clearance of AZT is probably due to the effect of probenecid on the active CSF-to-plasma transport of AZT. The model analysis also indicates that probenecid may have increased the plasma to CSF clearance of AZT. There was an increasing trend in the steady-state CSF/plasma AZT concentration ratio with increasing plasma probenecid concentrations. These results are consistent with probenecid competitively inhibiting the CSF-to-plasma transport of AZT.

Penetration of some compounds through blood-brain and blood-testis barriers in chronically hypertensive rats

Acute hypertension impairs the function of biological barriers, e.g. that of blood-brain barrier. We tested the hypothesis that chronic hypertension might influence the penetration of compounds through blood-brain and blood-testis barriers. With this in mind, the penetration of relatively small radioactive compounds (14C-2-methyl-4-chlorophenoxyacetic acid = 14C-MPA, 14C-sucrose and 14C-antipyrine, 5 microCi/kg intravenously) into the brain, liquor space and testis was compared in male normotensive (Wistar and chronically hypertensive SH rats (11-22 months old). In chronic hypertension after 14C-MCPA and 14C-sucrose administration the penetration of radioactivity into the brain, cerebrospinal fluid and testis had significantly decreased or showed evidence of decrease, while after 14C-antipyrine administration the penetration remained unchanged. Penetration of Evans blue-albumin complex into the brain was studied by giving intravenous injection of Evans blue (5% solution) which is firmly bound to serum albumin. Extravasation of dye-protein complex into the brain showed no difference between Wistar and SH rats. The results suggest that chronic hypertension does not increase the penetration of compounds into the brain and testis but rather, reduces it.