In VitroStimulation of Thyroid Ornithine Decarboxylase Activity and Polyamines by Thyrotropin*

Abstract

Thyrotropin (TSH) stimulation of ornithine decarboxylase (ODC) activity and polyamine levels was studied in vitro in rat thyroids. The elevation in ODC activity was related to the concentration of TSH in the incubation medium with peak activity at a concentration of 25 mU[milliunits]/ml. ODC activity with 50 mU/ml of TSH was 3-5-fold higher than control activity at 5 h of incubation; this stimulation was enhanced by the addition of 0.5 mM 3-isobutyl-l-methyl xanthine (MIX), a phosphodiesterase inhibitor. Dibutyryl cyclic AMP (DbcAMP) also stimulated ODC activity with a dose response up to 2.0 mM. The increase in ODC activity with TSH and MIX was prevented by incubation with actinomycin D (10 .mu.g/ml) or puromycin (0.2 mM). Putrescine concentrations in rat thyroids rose to 3 times basal levels after 6 h of incubation with TSH and MIX; no significant elevation in spermidine or spermine was observed after up to 7 h incubation. The increase in tissue putrescine preceded a rise in [3H]uridine incorporation into acid-soluble material that occurred at 7 h. Stimulation of thyroid ODC activity by TSH is mediated by cyclic AMP; the data further are consistent with a role for polyamines in the control of RNA synthesis in the thyroid.