Cultured Thyroid Cell Adenosine 3′,5′-Cyclic Monophosphate Response To Thyrotropin: Loss and Restoration of Sensitivity to Iodide Inhibition

Abstract

Unlike in all other thyroid preparations, exposure of dog thyroid cells in long-term monolayer culture to iodide (10(-7) to 10(-3) M for up to 19 h did not blunt the subsequent adenosine 3', 5'-cyclic monophosphate (cAMP) response to thyrotropin (TSH) stimulation. This lack of effect of iodide was observed even when confluent thyroid cells were "follicularized" by the action of TSH in the culture medium. Preincubation of these cells in thyroxine (T4) and triiodothyronine (T3) was similarly without effect on the subsequent cAMP response to TSH. Study of thyroid cells during the early phase of primary culture demonstrated that inhibition by iodide (10(-4) M) of the cAMP response to TSH occurred after 7 h but was lost after 48 h of cell culture. This inhibitory effect of iodide was prevented by the inclusion of methimazole in the preincubation medium. As with iodide-insensitive cells, T4 and T3 were without effect on the cAMP response to TSH in iodide-sensitive thyroid cells. Exposure of iodide-insensitive thyroid cells to iodide-containing medium obtained after 2 h of incubation with dog thyroid slices, as well as to medium enriched with the 100,000 g supernatant fraction of homogenates prepared from these thyroid slices, did not restore the inhibitory action of iodide. However, iodide-sensitivity of the cAMP response to TSH was restored by preincubation of iodide-insensitive cells in 10(-4) M iodide plus an H2O2-generating system (glucose-glucose oxidase). These data suggest that T4 and T3 are not organic iodine inhibitors of the thyroid cAMP response to TSH. In addition, they provide evidence against the existence of a soluble, freely diffusible, organic iodine inhibitor of thyroid adenylate cyclase. The loss of sensitivity to iodide inhibition of adenylate cyclase that occurs in thyroid cells shortly after initiation of primary culture appears to be related to a defect in the cellular organification mechanism, possibly the H2O2-generating system.

Iodine Suppression of Iodide Uptake in FRTL-5 Thyroid Cells

“…The last result contrasts with studies using primary cell cultures, slice, or follicle preparations from dog thyroid, where I~ pretreatment decreases the ability of TSH to raise cAMP levels (22)(23)(24)(25). In these studies (22)(23)(24)(25), however, the inhibitory effect of I~ on thyroid cell adenylate cyclase activation was lost after 1 day of primary culture and involved preincubation of cultures with medium without TSH for 4-16 h of this period.…”

“…In these studies (22)(23)(24)(25), however, the inhibitory effect of I~ on thyroid cell adenylate cyclase activation was lost after 1 day of primary culture and involved preincubation of cultures with medium without TSH for 4-16 h of this period. To see whether these conditions are important for I~ to effect FRTL-5 cells, grown and maintained in TSH (1 x 10" 10 M), were switched to medium without TSH and incubated for 16 h. At that time intracellular cAMP levels were determined under standard conditions (16) in the absence (basal) or presence of the noted concentrations of TSH as well as the agents in the preincubation.…”

Thyroid Autoregulation: Effect of Iodine on Glucose Transport in Cultured Thyroid Cells*

“…In these series of experiments porcine thyroid cells were used on the first day of primary culture because subsequently cells lose the ability to organify iodine (24). In preliminary studies, the influx of 2-DG at a concentration of 0.1 mM was linear for up to 30 min (data not shown).…”

Presence of a soluble inhibitor of thyroid iodination in primary cultures of thyroid cells

“…During the last decades thyroid cell cultures have been utilized as a model for the analysis of gland function and its regulation. However, it was noticed that monolayer primary cell cultures of pig (1)(2)(3) and dog (4,5) thyroid show a time-course decline of iodide organification and TPO activity. To date, unequivocal data on this issue are not available.…”