Age-Dependent Changes in the Regulation of Glycerolphosphate Dehydrogenase in the Rat Brain and in a Glial Cell Line

Abstract

This chapter pertains to some investigations on the role of four factors—namely, (1) concentration of glucocorticoids, (2) receptor activity and nuclear binding of the hormone, (3) RNA synthesis, and (4) protein synthesis in age-dependent changes of glycerolphosphate dehydrogenase (GPDH) concentration and inducibility in vivo and in glial cell cultures. Enzyme activity does represent enzyme concentration because, as McGinnis and de Vellis showed by immunochemical methods, GPDH in induced and basal states are identical enzymes. GPDH induction resides probably in glial cells for the following reasons. Firstly, it occurs in all brain regions, a characteristic somewhat inconsistent with the extreme diversity of types of neurons, and, therefore, more consistent with the probable uniformity of astrocytes. Similarly, S-100 protein, a brain-specific protein and a putative glial marker, is found only in tumors of glial cells. Thirdly, the developmental pattern of GPDH resembles that of two glial markers, S-100 protein and carbonic anhydrase. Finally, GPDH induction has only been observed in astrocytoma cell lines.