Yoshihiko Ueta

Differences in the electrophysiological response to I− and the inhibitory anions SCN∮- and C1O4−, studied in FRTL-5 cells

The electrophysiological properties of the Na+/I- symporter (NIS) were examined in a cloned rat thyroid cell line (FRTL-5) using the whole-cell patch-clamp technique. When the holding potential was between -40 mV and -80 mV, 1 mM NaI and NaSCN induced an immediate inward current which was greater with SCN- than with I-. The reversal potential for I- and SCN- induced membrane currents was +50 mV. This is close to the value of +55 mV calculated by the Nernst equation for Na+. These results are consistent with I- and SCN- translocation via the NIS that is energized by the electrochemical gradient of Na+ and coupled to the transport of two or more Na+. There was no change in the membrane current recording with ClO-4 indicating that ClO-4 was either not transported into the cell, or the translocation was electroneutral. ClO-4 addition, however, did reverse the inward currents induced by I- or SCN-. These effects of I-, SCN- and ClO-4 on membrane currents reflect endogenous NIS activity since the responses duplicated those seen in CHO cells transfected with NIS. There were additional currents elicited by SCN- in FRTL-5 cells under certain conditions. For example at holding potentials of 0 and +30 mV, 1 mM SCN- produced an increasingly greater outward current. This outward current was transient. In addition, when SCN- was washed off the cells a transient inward current was detected. Unlike SCN-, 1-10 mM I- had no observable effect on the membrane current at holding potentials of 0 and +30 mV. The results indicate FRTL-5 cells may have a specific SCN- translocation system in addition to the SCN- translocation by the I- porter. Differences demonstrated in current response may explain some of the complicated influx and efflux properties of I-, SCN- and ClO-4 in thyroid cells.

Evaluation of thyroid function in patients with isolated adrenocorticotropin deficiency

Thyroid hormone and thyrotropin (TSH) levels were evaluated before and after adrenal replacement in eight patients (six men and two women, 35-62 years old) with isolated adrenocorticotropin (ACTH) deficiency. Six patients (cases 1-6) showed TSH excess before treatment. Four patients (cases 1-4), who initially had subnormal thyroid hormone levels, showed resolution of biochemical features of primary hypothyroidism after treatment, although TSH excess has persisted in two patients (cases 1 and 2). Case 1 had an extremely high titer of antimicrosomal antibody (MCHA), and cases 2 and 3 showed histologically and cytologically chronic thyroiditis, despite negative results for MCHA and antithyroglobulin antibody, respectively. Two patients (cases 5 and 6), who had had normal thyroid hormone levels and did not show the significant rise in serum T3 in TSH releasing hormone testing, showed TSH normalization without changes in serum thyroid hormone levels after treatment. The other two patients (cases 7 and 8), who initially had normal TSH and thyroid hormone levels, did not show the significant changes in serum TSH and thyroid hormone levels after treatment. The prevalence of chronic thyroiditis coexistence in isolated ACTH deficiency may be higher than predicted. Therefore, TSH excess before adrenal replacement may be attributed to not only direct enhancement of TSH release due to chronic cortisol deficiency but also to thyroid dysfunction due to chronic thyroiditis. It is possible that hypothyroidism due to chronic thyroiditis can be improved only by adrenal supplementation.

A novel mutation causing complete deficiency of thyroxine binding globulin

Thyroxine binding globulin (TBG) is a serum protein that transports thyroxine. Three naturally occurring mutations have been reported to produce complete deficiency of TBG (TBG‐CD). The first to be reported was TBG‐CD5 in caucasian families of French‐Canadian origin and consists of substitutions in exons 2 and 3. TBG‐CD of English ethnic origin (TBG‐CD6) is characterized by a thymine deletion in codon 165 (exon 1). In Japanese families with TBG‐CD (TBG‐CDJ), a variant has been characterized with a deletion of the first base of the codon for amino acid 352 (exon 4) in the common type TBG. In this communication we report a new type of TBG‐CD in a family of japanese ethnic origin that is characterized by a single nucleotide substitution in place of two nucleotides in exon 1. This is an uncommon mutation which we have been unable to find in other genes.

Detection of Thyroid-Stimulating Antibody in Patients with Inflammatory Thyrotoxicosis

The detection of thyrotropin-binding inhibitory immunoglobulins (TBII) and/or thyroid-stimulating antibody (TSAb) has been reported in some patients with painless thyroiditis (PT) or subacute thyroiditis (SAT). However, its mechanism is unknown. TBII and TSAb measured using cultured FRTL-5 thyroid cells were evaluated in 18 patients with PT, 11 patients with SAT and a patient with SAT-like symptoms. In PT, we detected both TBII and TSAb activities in only 1 patient. This case had first come to our attention with subclinical hypothyroidism and had already had weakly positive TSAb activity (205.9%) 1 year before the present onset of PT. This patient had a transient thyrotoxicosis with a low uptake (24 h) of 123I (4.3%) and 821.0% TSAb activity, and subsequently developed a transient subclinical hypothyroidism. Even after 2 years, she still had positive TSAb activity (382.3%). In SAT, TBII and TSAb activities were not detected during the courses of any patients. A patient with transient thyrotoxicosis, who had a high uptake (30 min) of 99mTc (5.6%) and SAT-like symptoms (painful tenderness on right thyroid lobe and markedly accelerated erythrocyte sedimentation rate), showed positive activities of TBII (34.9%) and TSAb activity (1,366.9%). Histological findings by thyroid needle biopsy performed in the thyrotoxic phase showed coexistence of granulomatous inflammatory changes and hyperplasia with papillary folds of some residual follicular cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoimmune Thyroiditis with Transient Thyrotoxicosis: Comparison between Painful Thyroiditis and Painless Thyroiditis

Clinical and laboratory findings and long-term outcomes in 8 patients (7 women) with autoimmune thyroiditis (AT), aged 34-59 years, who had a painful tender goiter and a transient thyrotoxicosis with a low thyroid radioactive iodine uptake (RAIU), were compared with those in 15 patients (13 women) with painless thyroiditis (PT), aged 23-69 years. Six painful AT and 6 PT patients had a history of prior awareness of goiter. All patients with painful AT had a moderate or marked elevation of erythrocyte sedimentation rate and a positive result for C-reactive protein, while only 3 PT patients (group B) did. There were no significant differences between the mean age, duration of symptoms, white blood cell count, serum triiodothyronine (T3) and thyroxine (T4) concentrations, serum T3/T4 ratio and duration of thyrotoxicosis after the initial examination and prevalences of positive results for antithyroglobulin and -microsomal antibodies in the two diseases. Two of 8 painful AT patients showed a histologically chronic fibrous variant and 6 others showed chronic lymphocytic thyroiditis. All PT patients examined also showed lymphocytic thyroiditis. Two and 5 painful AT patients developed transient and persistent hypothyroidism, respectively, while 8 [7 in group A (normal ESR), 1 in group B] and 3 PT patients (1 in group A, 2 in group B) did, respectively. The mean serum thyroid-stimulating hormone level in the hypothyroid phase in painful AT patients was higher than that in PT patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequential changes in serum thyroglobulin, triiodothyronine, and thyroxine following partial thyroidectomy for nontoxic nodular goiter

The sequential changes in serum thyroglobulin (Tg), thyroxine (T4), free thyroxine (FT4), triiodothyronine (T3) and thyrotropin (TSH) were evaluated in ten patients on whom partial thyroidectomy for nontoxic nodular goiter had been performed. These changes were compared with those in ten patients who underwent upper abdominal surgery (cholecystectomy) under similar anesthesia, and whose calorie and fluid intake was similar until at least 48 hours after surgery. In agreement with previous reports, marked elevations in serum Tg that reached peak concentration (660 to 1350 ng/mL) at one or two hours after the thyroid incision (mean +/- SD; 787 +/- 304.0 ng/mL and 839 +/- 345.7 ng/mL, respectively) were observed. On the other hand, the significant but minimal increases in serum T4 and FT4 were observed at 24 hours (P less than .001 and P less than .001, respectively), 48 hours (P less than .01 and P less than .001, respectively), and 72 hours (P less than .01 and P less than .01, respectively) after the thyroid incision compared with the level just prior to the thyroid incision. Similarly, serum T3 also increased significantly at 6 to 168 hours after the thyroid incision (P less than .01, P less than .05, P less than .05, P less than .05, and P less than .05, respectively). These increases in serum T4, FT4 and T3 were not observed in the cholecystectomy patients. The mean serum TSH levels at 24 to 72 hours after thyroid incision and those at 6 to 48 hours after the abdominal incision were significantly decreased compared with those before thyroid and abdominal incision, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of diabetes mellitus on thyrotropin response to thyrotropin-releasing hormone in untreated acromegalic patients

Impairment of thyrotropin (TSH) response to thyrotropin-releasing hormone (TRH) has been documented in patients with uncontrolled diabetes mellitus (DM). In acromegalic patients, however, there have been no data regarding TSH secretion studied taking the existence of DM into consideration. Therefore, we investigated the TSH response to TRH [expressed as TSH increment (†TSH)] in 14 untreated acromegalic patients, who did not show the suprasellar extension of adenoma, divided into two groups on the basis of either presence or absence of uncontrolled DM, and in 28 normal subjects. The mean max †TSH was significantly reduced (p< 0.02) in acromegalic patients despite similar mean serum T4 and free T4 index (FT41) levels. Furthermore, the mean basal and max †TSH in 7 patients with DM (FBS, 120–300 mg/dl; HbA1, 8.8–15.2%) were significantly lower than those in 7 patients without DM (p<0.05 and p<0.02, respectively) despite similar the mean serum T3, T4, FT41, growth hormone (GH) and prolactin (PRL) levels and sellar volume. In 4 patients with DM the TSH response to TRH 6–8 weeks after insulin therapy, when their HbA1 levels were normal, increased compared to that before insulin therapy. The mean max †TSH after selective adenomectomy in 8 patients (3 in DM group and 5 in non-DM group), whose fasting basal GH fell to less than 5 ng/ml, was almost identical to that in normal subjects. In conclusion, the present study suggests that the abnormality in TSH secretion in acromegalic patients may be increased by the existence of uncontrolled DM.

Amitriptyline inhibits the G protein and K+ channel in the cloned thyroid cell line

We have reported that thyroid K+ channel is activated by extracellular application of the thyroid-stimulating hormone (TSH) using single channel recording method performed on cloned normal rat thyroid cell (FRTL-5) membrane. Treatment of dibutyryladenosine cyclic monophosphate (Bt2 cAMP) also activated the TSH-dependent K+ channel. These findings indicate that the thyroid K+ channel is activated through the TSH-adenosine cyclic monophosphate (cAMP)-protein kinase A system. We examined the effects of amitriptyline on TSH-guanosine triphosphate binding protein (G protein)-adenylate cyclase-cAMP-K+ channel system in the cloned normal rat thyroid cell line FRTL-5. Amitriptyline inhibited the cAMP production induced by TSH. Amitriptyline also inhibited the cAMP production induced by cholera toxin, indicating that amitriptyline inhibited the thyroid G protein. Amitriptyline had no effect on TSH-receptor binding and cAMP production by forskolin (adenylate cyclase stimulator). Amitriptyline inhibited the K+ channel activation by cAMP, indicating that the suppressing mechanism is not the inhibition of TSH receptor or G protein but the direct suppression of K+ channel. It was concluded that amitriptyline inhibited the thyroid G protein and K+ channel.