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 10 40 . 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 fig/ing 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. (Endocrinology 82: 342, 1968)
The single-cell plating technique was used to develop four clonal cell lines that perform organ-specific functions after being serially cultured for prolonged periods. These strains include steroid-secreting Leydig cells, melanomacells that form pigment, and two strains from a hormone-secreting rat pituitary tumor. One of the cell lines from the pituitary tumor secretes growt hormone, while another line derived from the same tumor secretes a substance similar to adrenocorticotropic hormone.
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