Uptake of triiodothyroacetic acid and its effect on thyrotropin secretion in cultured anterior pituitary cells.

Abstract

The uptake of ['251]triiodothyroacetic acid ([lzSI]Triac) in anterior pituitary cells was investigated and compared with that of ['251]T3. Furthermore, the effects of Triac, T,, and Tq on TSH release were compared. Cells isolated from adult male Wistar rats were cultured for 3 days in medium with 10% fetal calf serum. Uptake was measured at 37 C with ['251]Triac (100,000 cpm; 120 PM) or ["?]T3 (50,000 cpm; 50 PM) in medium with 0.5% BSA. In this medium, the ratio of the free fractions of Triac, TB, and T1 was 1:8:1. Exposure of cells to 100 nM TRH for 2 h stimulated TSH release by 80-110% (P < 0.001). Comparing total hormone levels (1 nM to 1 jtM), Triac and TS were equally effective in reducing this response, and both were lo-fold more effective than T,. The time-course (15 min to 4 h) of ["'I]Triac uptake was similar to that of [?)Ta, showing equilibrium after 1 h. Unlabeled Triac (1 pM) reduced the uptake of ['Z51]Triac and [lz51]T, at all time intervals. Expressed per pM free hormone, the cellular and nuclear uptake of ["'I]Triac were twice those of ['251]T3. The 15-min uptake of

Uptake of triiodothyronine and triiodothyroacetic acid in neonatal rat cardiomyocytes: effects of metabolites and analogs

“…As shown previously (Everts et al 1994), the free fractions of T 3 and Triac in medium with 0·5% BSA were 3·45 0·19% (n=8) and 0·41 0·03% (n=5) respectively -a ninefold difference. In the present study, the free T 3 fraction was not changed by the addition of 10 µM unlabeled T 3 , 3,3 -T 2 , 3,5-T 2 , Triac or Tetrac, and only slightly by 10 µM T 4 (4·21%; n=2).…”

“…When the 2-h cellular uptakes of T 3 and Triac were measured and expressed as percentages of the doses, a fivefold greater value for T 3 was observed, whereas the relative inhibition by 10 µM of the respective unlabeled hormone was roughly the same. Together, these findings indicate that Triac is taken up by cardiomyocytes and bound to their nuclear receptors, as in pituitary cells (Everts et al 1994). In contrast to pituitary cells, in which T 3 uptake was inhibited by Triac and vice versa (Everts et al 1994), the 15-min T 3 uptake in cardiomyocytes was not significantly inhibited by increasing concentrations of Triac.…”

“…Comparison of the time-courses of T 3 and Triac uptake in neonatal rat cardiomyocytes showed that, when expressed as fmol/pM free hormone, Triac uptake was about 30% greater than that of T 3 , but the difference was not as large as in cultured pituitary cells, in which an almost twofold difference was found (Everts et al 1994). When the 2-h cellular uptakes of T 3 and Triac were measured and expressed as percentages of the doses, a fivefold greater value for T 3 was observed, whereas the relative inhibition by 10 µM of the respective unlabeled hormone was roughly the same.…”

“…Although culturing cardiomyocytes in the presence of serum may result in proliferation of contaminating fibroblasts that also show thyroid hormone transport (Docter et al 1987), we have previously shown that uptake of thyroid hormones is comparable in cardiomyocytes cultured for 5 days in absence or presence of serum (Everts et al 1996b, Verhoeven et al 2001 (Everts et al 1994(Everts et al , 1996b. Cells were preincubated (0·5 ml) for 30 min and incubated (0·25 ml) for from 15 min to 24 h at 37 C without or with 10 µM unlabeled T 3 , Triac, Tetrac, 3,3 -T 2 , 3,5-T 2 , or 1 nM-10 µM DITPA, T 3 , T 4 or Triac, and in all cases After incubation, the medium was removed and the cells were washed with 1 ml ice-cold saline to remove tracer not bound to the cells.…”

“…With the purpose of suppressing thyrotropin (TSH) secretion in patients with thyroid cancer (Pujol et al 2000), triiodothyroacetic acid (Triac) has been tested for specificity at the pituitary and the peripheral level (Beck-Peccoz et al 1988, Sherman & Ladenson 1992, Everts et al 1994, Sherman et al 1997. In addition, tetraiodothyroacetic acid (Tetrac) was more potent than T 4 in reducing TSH release in isolated pituitary cells (Everts et al 1995) and in hypothyroid rats (Lameloise et al 2001), but it was less efficient in inducing cardiac hypertrophy (Lameloise et al 2001).…”