Distribution of physostigmine and metabolites in brain subcellular fractions of the rat

The distribution of 3H-physostigmine (Phy) has been studied in the rat brain subcellular fractions at various time intervals following i.v. injection.3H-Phy or its metabolites rapidly accumulate into the cytoplasm of cells and penetrates the intracellular compartments. Kinetic studies of the subcellular distribution of radioactivity (RA) per gm of rat brain following i.v. injection of 3H-Phy show peak concentrations at 30 min in all subcellular fractions with the exception of mitochondria. In the mitochondrial fraction the RA levels continue to rise from 4682 ± 875 DPM/gm at 5 min to 27474 ± 2825 DPM/gm at 60 min (P<.05). The cytosol contains the highest RA: 223341 ± 21044 DPM/gm at 30 min which declined to 53475 ± 3756 DPM/gm at 60 min. RA in synaptosome, microsomes and myelin increases from 5 to 30 min, and declines at 60 min. In vitro studies did not show a greater uptake of RA by the mitochondrial or synaptosomal fractions.The finding of relatively high concentrations of RA in the mitochondrial fraction at 60 min increases the likelihood that Phy or its metabolites could interfere with the physiological function of this organelle.