title: Ionic mechanisms regulating thyroidal secretion: effects of ouabain and medium sodium concentration on radioiodine release from cultured porcine thyroid cells.
abstract: Thyrotrophin stimulated release of radioiodine from the organic iodine pool of cultured porcine thyroid cells. The response was well developed within 2-4 h of incubation. Inhibition of the Na+/K+ pump with ouabain or incubation in sodium-free medium inhibited the response to TSH. The magnesium content of cultures was reduced by ouabain, and increasing the magnesium concentration of the medium to 10 mmol/l reversed the inhibition of the TSH response by ouabain. After prolonged incubation (4-6 h), ouabain in magnesium-enriched medium stimulated release of radioiodine. Its effects were not additive with those of TSH. Incubation for 4-6 h in media of reduced sodium concentration (34 mmol/l) also stimulated release. Sodium-free medium alone did not alter basal release rates, but magnesium enrichment of sodium-free medium promoted release after 4 h of incubation. It was concluded that the previously reported inhibition of the TSH response in thyroid tissue by ouabain or sodium-free medium was due to secondary derangements of cellular function rather than to a specific blockade of the secretomotor signal. The data are consistent with the hypothesis that a reduction in the sodium ion electrochemical gradient across the cell membrane mediates the secretomotor effect of TSH.
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D007455:Iodine / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology*; D013552:Swine; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism*; D013972:Thyrotropin / Q000037:antagonists & inhibitors* / Q000494:pharmacology
chemical_list: D010042:Ouabain; D013972:Thyrotropin; D007455:Iodine; D012964:Sodium; D008274:Magnesium