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Three clonal strains of epithelial cells were established from a transplantable rat pituitary tumor. These strains have been serially propagated for 14–25 months. They were subcultured every 2–3 weeks. Cells of the original strain have increased by a factor of more than 1040. The generation times of the 3 lines 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 figμng cell nitrogen/24 hr for the most vigorous strain. There has been no decrease in the rate of cell division nor decline in growth hormone secretion since the cells were established in culture. (Endocrinology82: 342, 1968)
Tashjian et al. (Thu,) studied this question.