Cells derived from a retinoblastoma from a 3-year-old boy have been cultured for two years; these cells have no glutamine synthetase activity. Evidence is presented that a normal human retina of this age should have appreciable amounts of this enzyme activity. The tumor derived cells can be induced for the enzyme by 14 or more days treatment with 0.5μg to 1.0μg/ml of cortisol.
Reif-Lehrer L. Glutamine Synthetase Activity in Human Retinal TissueEnzyme Activity in the Normal Retina and Cortisol Induction in Cultured Cells Derived From Retinoblastoma. Arch Ophthalmol. 1971;86(1):72-76. doi:10.1001/archopht.1971.01000010074014