As characterized by mean doubling time (Td) and plating efficiency, the growth of the T–l human kidney cell line has been shown previously to be affected by the introduction of T4 and T3 to the growth medium. Reducing the content of fetal bovine serum (FBS) from 10 to 2.5% of the medium prolongs Td (from 22.6 to 37.8 hr) and depresses PE (from 80.3 to 29.5%). Diminution of the serum concentration, also, augments profoundly the sensitivity to and specificity for these thyroidal hormones. Thus, the addition of 4.45 X 1 0- 7M of T3 to T–l cells incubated in 2.5% FBS medium reduced Td to 26.5 hr, a relative shortening of 42.4%. If a relative mean rise of 10% in PE is taken as the minimum discernible, T–l cells grown in 2.5% FBS respond to as little as 2.5 X 10-9M for T4 or 2.0 X 1 0-10M for T3. Similarly performed tests for specificity (by introducing 4.45 X 10-6M for each of the substances evaluated) indicated that DIT was very potent, MIT considerably less so, and tyrosine, leucine, and iodide had nearly no influence. In this manner, it was demonstrated also that L—T4 is more active than D–T4. The T–l cell system is evidently an interesting in vitro model for exploring the peripheral effects and metabolism of thyroidal hormones, related iodinated amino acids, and analogues. (Endocrinology91: 580,1972)
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Edward T. Siegel (1972) studied this question.