REACTIONS OF ASTROCYTES AND MICROGLIAL CELLS AROUND HEMATOGENOUS METASTASES OF THE HUMAN BRAIN - EXPRESSION OF ENDOTHELIN-LIKE IMMUNOREACTIVITY IN REACTIVE ASTROCYTES AND ACTIVATION OF MICROGLIAL CELLS

An immunohistochemical study was made on the peritumoral gliosis which is produced around hematogenous metastases of the human brain. The material was derived from 73 autopsy cases with different primary malignancies and six control cases without evidence of brain disease. Reactive astrocytes of hypertrophic and gemistocytic types were present around and within all the metastases. Eighty-five percent of the cases with metastases showed expression of endothelin-like immunoreactivity in the peritumoral astrocytes. Such immunoreactive astrocytes were not present in the normal controls but have previously been found in reactive astrocytes around infarcts, lacunas, inflammatory and degenerative brain diseases. The endothelin-like immunoreactivity probably reflects an increased intracellular content of endothelin. If this peptide is released from the reactive astrocytes it may act as a mitogen and influence microcirculation by inducing vasoconstriction. Activation of microglial cells, detected by ferritin immunohistochemistry, was another frequent and widespread glial cell alteration around the metastases. In conclusion, the reactive gliosis, which is formed around metastases involves activated astrocytes as well as activated microglial cells. Both cell types can release numerous biologically active compounds which may influence the structure and function of the brain tissue around the metastases.