Establishment of Clonal Strains of Rat Pituitary Tumor Cells That Secrete Growth Hormone1,2

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Abstract
Three clonal strains of epithelial cells were established from a transplantable rat pituitary tumor. These strains were serially propagated for 14-25 months. They were subcultured every 2-3 weeks. Cells of the original strain increased by a factor of more than 10[degree]. The generation times of the 3 lines were were similar and ranged between 30 and 40 hr. Cells of all 3 strains synthesize growth hormone and secrete it into the culture medium. Growth hormone synthesized in vitro is indistinguishable from normal rat pituitary growth hormone as measured by micro-complement fixation and radioimmunoassay. The specific activity of growth hormone production was estimated to be 20-40 [mu]g/mg cell N/24 hr. for the most vigorous strain. There was no decrease in the rate of cell division nor decline in growth hormone secretion since the cells were established in culture.