Effects of caffeine and ethanol on the blood-brain barrier in rats.

In rats, pretreatment with caffeine or ethanol shortens the duration of the harmine tremor and decreases the brain concentrations of this alkaloid. Caffeine and ethanol do not influence the plasma concentration of harmine, its plasma protein binding and its cerebral concentration at the termination of the tremor. The findings are regarded as indicative of a reduction by caffeine and ethanol of the blood-brain barrier permeability to harmine.