Thyroxine secretion by isolated hog thyroid cells: A cyclic AMP independent pathway

Rousset, Bernard; Munari, Y; Rostagnat, Anne; Mornex, R

doi:10.1016/0303-7207(77)90044-2

Cited by 5 publications

(1 citation statement)

References 13 publications

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“…The existence of an extracellular iodinating activity in thyroid cell suspension is in keeping with the fact that thyroid peroxidase is a firmly bound membrane component that could still be present after the trypsin-treatment procedure. Another cell membrane component, the hormone receptor, persisted after trypsin treatment, as evidenced by the cell responsiveness to thyrotropin (Rousset et al, 1977).…”

Section: Discussionmentioning

confidence: 99%

Intracellular and extracellular sites of iodination in dispersed hog thyroid cells

Rousset¹,

Poncet²,

Dumont³

et al. 1980

Biochemical Journal

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Iodination and hormone synthesis has been studied in isolated hog thyroid cells in suspension. We characterized three iodination processes by use of pharmacological agents. (1) Intracellular iodination dependent on active iodide transport, which was inhibited by NaClO4 or ouabain, but not by catalase. This iodination was linear for 6h with no apparent Km for iodide of 1.5 muM, was stimulated by thyrotropin or N6O2'-dibutyryladenosine 3':5'-cyclic monophosphate, yielded mostly iodinated thyroglobulin and was efficient for tetraiodothyronine synthesis. (2) Extracellular iodination, which was sensitive to catalase, but not to NaClO4 or ouabain. This iodination plateaued after 2h and the apparent Km was 16.5 muM. This process was insensitive to thyrotropin and dibutyryl cyclic AMP. The major products were iodoprotein other then thyroglobulin and iodolipid and the yield of tetraiodothyronine was low. (3) Intracellular iodination from passively diffused iodide, which was not sensitive to inhibitors. Other characteristics of passive intracellular iodination were intermediate between active intracellular iodination and extracellular iodination. The fact that the three processes are inhibited by similar concentrations of methimazole, and their apparent Km values, when corrected for the concentrating effect of iodide trapping, are all of the same order as the Km of purified thyroid peroxidases, suggest that although their locations are different, the enzymic systems involved are identical. These results show that, besides an extracellular site of iodination, dispersed thyroid cells process an intracellular site of iodination with biochemical characteristics of physiological relevance.

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Section: Discussionmentioning

confidence: 99%

Intracellular and extracellular sites of iodination in dispersed hog thyroid cells

Rousset¹,

Poncet²,

Dumont³

et al. 1980

Biochemical Journal

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Antithyroid effect of a food or drug preservative: 4-hydroxybenzoic acid methyl ester

Rousset

1981

Experientia

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Summary. 4-hydroxybenzoic acid methyl ester (methylparaben) inhibits organification of iodide by isolated hog thyroid cells. The concentration which produces a 50% inhibition was about 2.0 x 10-4M. A similar inhibition was observed in nonstimulated and TSH-or dibutyryl cyclic AMP-stimulated cells. Neither iodide uptake nor cyclic AMP generation were altered by methylparaben.Antithyroid drugs refer to a group of compounds that block the synthesis of thyroid hormones. These compounds fall into 2 main categories: a) compounds that inhibit accumulation of iodide by the thyroid gland, b) compounds that interfere with the utilization of iodide into the gland. The compounds of the 2nd group exert their inhibitory effect by blocking one or several of the following reactions: oxydation of iodide, formation of iodotyrosines, coupling of iodotyrosines to form thyroid hormones. Besides, thionamides which are the most potent antithyroid agents, phenol and benzoic acid derivatives (resorcinol, p-aminobenzoic acid ...) are known to be efficient inhibitors of iodine metabolism both in vivo and in vitro. During the course of our study on the metabolism of iodide in dispersed thyroid cells, we found that 4-hydroxybenzoic acid methyl ester, a compound used as a food or drug preservative, prevented thyroid hormone synthesis. In this communication we report that this compound inhibits the organification of iodide without altering the iodide trapping mechanism. Suspensions of dispersed hog thyroid cells were prepared as previously described I. Thyroid cells (1 5 • 107) were incubated in Earle's balanced salt solution, pH 7.4, in the presence of 0.05/~M iodide labelled with 1-5/~Ci 131I, for 2 h at 37 ~ with air as the gas phase and under constant shaking (60 cycles/rain). Iodide trapping, expressed in terms of 1311-C/M ratio: the ratio between intracellular and medium labelled iodide concentration, was determined in the presence of 2 mM methimazole according to Rodesch and Dumont:. Iodide organification was assessed by measurements of 13q-iodide incorporation into acid-insoluble material (mainly iodoproteins). Cell homogenates were supplemented with 0.1 ml 0.2 mM NaI and 0.1 ml 1% (w/v) bovine serum albumin and proteins were precipitated with 5~ (w/v) trichloracetic acid. The 1500• g pellet was washed with 5% trichloracetic acid and counted for radioactivity. Cyclic AMP was assayed as previously described 3. Thyrotropin (TSH),N6,O2'-dibutyryl-adenosine 3':5' monophosphate (db cAMP) and 4-hydroxybenzoic acid methyl ester were obtained from Armour (Kankakee, USA), Sigma (St. Louis, USA) and Organon (France), respectively.

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In vitro studies of the thyroglobulin degradation pathway: endocytosis and delivery of thyroglobulin to lysosomes, release of thyroglobulin cleavage products — iodotyrosines and iodothyronines

et al. 1989

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Thyroxine secretion by isolated hog thyroid cells: A cyclic AMP independent pathway

Cited by 5 publications

References 13 publications

Intracellular and extracellular sites of iodination in dispersed hog thyroid cells

Intracellular and extracellular sites of iodination in dispersed hog thyroid cells

Antithyroid effect of a food or drug preservative: 4-hydroxybenzoic acid methyl ester

In vitro studies of the thyroglobulin degradation pathway: endocytosis and delivery of thyroglobulin to lysosomes, release of thyroglobulin cleavage products — iodotyrosines and iodothyronines

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