Neutral and acid sphingomyelinases: somatotopographical distribution in human brain and distribution in rat organs. A possible relationship with the dopamine system.

Acid and neutral sphingomyelinase activities have been measured in 22 regions of human brain, and in several rat organs. In general, acid sphingomyelinase activity was similar in most brain regions examined. By contrast neutral sphingomyelinase activity decreased 30-fold between the globus pallidus and white matter. In grey matter structures activity decreased in the order globus pallidus greater than substantia nigra greater than or equal to putamen greater than head of caudate greater than thalamus greater than cortical structures. Under the conditions of assay and in the presence of several possible donors or acceptors, there was no evidence of transfer of phosphoryl-choline to other lipid acceptors. Acid sphingomyelinase was ubiquitously distributed in all rat tissues examined, highest in liver and lowest in adipose tissue. Neutral sphingomyelinase activity was highest in brain; activity from 25 to 10% of that in brain was observed in testis, adrenal gland and aorta. Activity in the other organs examined was less than 10% of that in brain. We suggest that the neutral enzyme serves a special function in brain, perhaps related to the dopaminergic systems.