Increase in the penetration of tracer compounds into the rat brain during 2-methyl-4-chlorophenoxyacetic acid (MCPA) intoxication.

The penetration of different intravenous tracer molecules such as 14C-labelled 2-methyl-4-chlorophenoxyacetic acid (14C-MCPA), 14C-p-aminobenzoic acid (14C-PABA), 14C-sucrose, 14C-antipyrine and iodinated (125I) human albumin (125I-HA) into the brain and cerebrospinal fluid (CSF) was studied in MCPA-intoxicated and control rats. Toxic subcutaneous doses of sodium salt of MCPA (200-500 mg/kg) increased highly the brain/plasma and CSF/plasma ratios of 14C-MCPA and 14C-PABA, as compared to the muscle/plasma ratio. Probenecid (200 mg/kg) did not affect the cerebral MCPA concentration in the intoxicated animals. The tissue/plasma ratios of 14C-sucrose, 14C-antipyrine and 125I-HA were also increased in the brain and CSF of intoxicated animals, but the increases were less pronounced than those of 14C-MCPA or 14C-PABA. The results indicate that MCPA intoxication caused a selective damage of the blood-brain barrier in the brain areas studied.