To investigate the uptake of triiodothyronine sulfate (T3S) and its effect on thyrotropin-releasing hormone (TRH)-induced thyrotropin (TSH) secretion, anterior pituitary cells were isolated from euthyroid rats and cultured for 3 days in medium containing 10% fetal calf serum. Incubation was performed at 37°C in medium containing 0.5% bovine serum albumin (BSA). Exposure of the pituitary cells to TRH (0.1 μmol/L) for 2 hours stimulated TSH secretion by 176%. This effect was reduced by approximately 45% after a 2-hour preincubation with T3 (0.001 to 1 μmol/L). A significant inhibitory effect of T3S on TRH-induced TSH release was only observed at a concentration of 1 μmol/L. The uptake of [125I]T3 after 1 hour of incubation was reduced by 40% ± 4% (P < .001) by simultaneous addition of 10 nmol/L unlabeled T3, whereas 1 μmol/L T3S was required to obtain a reduction of the [125I]T3 uptake by 34% ± 2% (P < .001). The amount of T3 present in the unlabeled T3S preparation was 0.25% as determined by radioimmunoassay. When pituitary cells were incubated for 1 hour with [125I]T3S or [125I]T3 both 50,000 cpm/0.25 mL), the uptake of [125I]T3zS expressed as a percentage of the dose was 0.04% ± 0.02% (mean ± SE, n = 4), whereas that of [125I]T3 amounted to 3.0% ± 0.4% (n = 4). In contrast, when hepatocytes were incubated for 1 hour with [125I]T3S, the uptake amounted to 5.1% ± 0.8% (n = 9), whereas that of [125I]T3 was 22.1% ± 1.7% (n = 9). Furthermore, [125I]T3S was as rapidly deiodinated (iodide production, 14.9% ± 2.6%; n = 9) as [125I]T3 (12.1% ± 0.8%, n = 9) by hepatocytes. It is concluded that (1) T3S is poorly taken up by pituitary cells, and (2) the suppressive effect of high concentrations of T3S on TRH-induced TSH secretion and on [125I]T3 uptake can be explained by slight contamination with T3. Thus, it appears that T3S has only a minor biological effect, if any, on the pituitary.,
Metabolism: clinical and experimental
Department of Nuclear Medicine

Everts, M., Visser, T., van Buuren, J. C. J., Docter, R., de Jong, M., Krenning, E., & Hennemann, G. (1994). Uptake of triiodothyronine sulfate and suppression of thyrotropin secretion in cultured anterior pituitary cells. Metabolism: clinical and experimental, 43(10), 1282–1286. doi:10.1016/0026-0495(94)90223-2