The effect of recombinant human thyrotropin (rhTSH) on thyroid function in mice and rats

Endocrine Diagnostics for Exotic Animals

Endocrine disease in exotic species is less common than in small animals. Nevertheless, the diagnostic principles used in small animals can be adapted to evaluate endocrine disease in many of the exotic species although species-specific aspects need to be considered. This article covers important diseases such as thyroid dysfunction in reptiles and birds, hyperthyroidism in guinea pigs, and hyperadrenocorticism in ferrets. Glucose metabolism in neoplasms affecting normal physiology, such as insulinoma in ferrets and gastric neuroendocrine carcinoma in bearded dragons, is discussed. Calcium abnormalities, including metabolic bone disease in reptiles and hypocalcemia in birds, are also covered.

Proteomic Analysis of Iodinated Contrast Agent-Induced Perturbation of Thyroid Iodide Uptake

(1) Background: We recently showed that iodinated contrast media (ICM) reduced thyroid uptake of iodide independently of free iodide through a mechanism different from that of NaI and involving a dramatic and long-lasting decrease in Na/I symporter expression. The present study aimed at comparing the response of the thyroid to ICM and NaI using a quantitative proteomic approach. (2) Methods: Scintiscans were performed on ICM-treated patients. Micro Single-Photon Emission Computed Tomography (microSPECT/CT) imaging was used to assess thyroid uptakes in ICM- or NaI-treated mice and their response to recombinant human thyroid-stimulating hormone. Total thyroid iodide content and proteome was determined in control, NaI-, or ICM-treated animals. (3) Results: The inhibitory effect of ICM in patients was selectively observed on thyroids but not on salivary glands for up to two months after a systemic administration. An elevated level of iodide was observed in thyroids from NaI-treated mice but not in those from ICM animals. Exposure of the thyroid to NaI modulates 15 cellular pathways, most of which are also affected by ICM treatment (including the elF4 and P706SK cell signaling pathway and INSR identified as an upstream activator in both treatments). In addition, ICM modulates 16 distinct pathways and failed to affect thyroid iodide content. Finally, administration of ICM reduces thyroid-stimulating hormone (TSH) receptor expression which results in a loss of TSH-induced iodide uptake by the thyroid. (4) Conclusions: Common intracellular mechanisms are involved in the ICM- and NaI-induced reduction of iodide uptake. However, ICM fails to affect thyroid iodide content which suggests that the modulation of these common pathways is triggered by separate effectors. ICM also modulates numerous distinct pathways which may account for its long-lasting effect on thyroid uptake. These observations may have implications in the management of patients affected by differentiated thyroid carcinomas who have been exposed to ICM. They also provide the basis for the utilization of ICM-based compounds in radioprotection of the thyroid.

Quantitative Measurement of the Thyroid Uptake Function of Mouse by Cerenkov Luminescence Imaging

Cerenkov luminescence imaging (CLI) has been an evolutional and alternative approach of nuclear imaging in basic research. This study aimed to measure the ¹³¹I thyroid uptake of mouse using CLI for assessment of thyroid function. Quantification of ¹³¹I thyroid uptake of mice in euthyroid, hypothyroid and hyperthyroid status was performed by CLI and γ-scintigraphy at 24 hours after injection of ¹³¹I. The ¹³¹I thyroid uptake was calculated using the equation: (thyroid counts − background counts)/(counts of injected dose of ¹³¹I) × 100%. Serum T4 concentration was determined to evaluate the thyroid function. The radioactivity of ¹³¹I was linearly correlated with the CL signals in both in vitro and in vivo measurements. CLI showed a significant decrease and increase of ¹³¹I thyroid uptake in the mice in hypo- and hyperfunctioning status, respectively, and highly correlated with that measured by γ-scintigraphy. However, the percent thyroid uptake measured by CLI were one-fifth of those measured by γ-scintigraphy due to insufficient tissue penetration of CL. These results indicate that CLI, in addition to nuclear imaging, is able to image and evaluate the ¹³¹I thyroid uptake function in mice in preclinical and research settings.

Single-Photon Emission Computed Tomography for Preclinical Assessment of Thyroid Radioiodide Uptake Following Various Combinations of Preparative Measures

BACKGROUND

MicroSPECT/CT imaging was used to quantitatively evaluate how iodide uptake in the mouse thyroid is influenced by (i) route of iodine administration; (ii) injection of recombinant human thyrotropin (rhTSH); and (iii) low iodide diet (LID) in euthyroid and triiodothyronine (T3)-treated mice.

METHODS

Pertechnetate (^99mTcO₄^-) and ¹²³I thyroid uptake in euthyroid and T3-treated animals fed either a normal-iodine diet (NID) or an LID, treated or not with rhTSH, and radiotracer administered intravenously, subcutaneously, intraperitoneally or by gavage, were assessed using microSPECT/CT imaging. Western blotting was performed to measure sodium/iodide symporter expression levels in the thyroid.

RESULTS

Systemic administration of radioiodide resulted in a higher (2.35-fold in NID mice) accumulation of iodide in the thyroid than oral administration. Mice fed LID with systemic radioiodide administration showed a further two-fold increase in thyroid iodide uptake to yield a ∼5-fold increase in uptake compared to the standard NID/oral route. Although rhTSH injections stimulated thyroid activity in both euthyroid and T3-treated mice fed the NID, uptake levels for T3-treated mice remained low compared with those for the euthyroid mice. Combining LID and rhTSH in T3-treated mice resulted in a 2.8-fold higher uptake compared with NID/T3/rhTSH mice and helped restore thyroid activity to levels equivalent to those of euthyroid animals.

CONCLUSIONS

Systemic radioiodide administration results in higher thyroidal iodide levels than oral administration, particularly in LID-fed mice. These data highlight the importance of LID, both in euthyroid and T3-treated, rhTSH-injected mice. Extrapolated to human patients, and in the context of clinical guidelines for the preparation of differentiated thyroid cancer patients, our data indicate that LID can potentiate the efficacy of rhTSH treatment in T3-treated patients.

American Thyroid Association Guide to investigating thyroid hormone economy and action in rodent and cell models

BACKGROUND

An in-depth understanding of the fundamental principles that regulate thyroid hormone homeostasis is critical for the development of new diagnostic and treatment approaches for patients with thyroid disease.

SUMMARY

Important clinical practices in use today for the treatment of patients with hypothyroidism, hyperthyroidism, or thyroid cancer are the result of laboratory discoveries made by scientists investigating the most basic aspects of thyroid structure and molecular biology. In this document, a panel of experts commissioned by the American Thyroid Association makes a series of recommendations related to the study of thyroid hormone economy and action. These recommendations are intended to promote standardization of study design, which should in turn increase the comparability and reproducibility of experimental findings.

CONCLUSIONS

It is expected that adherence to these recommendations by investigators in the field will facilitate progress towards a better understanding of the thyroid gland and thyroid hormone dependent processes.

Use of recombinant human thyroid-stimulating hormone for thyrotropin stimulation testing in euthyroid ferrets

OBJECTIVE

To evaluate the effects of IM administration of recombinant human thyroid-stimulating hormone (rhTSH) on plasma total thyroxine (T4) concentrations in euthyroid ferrets.

DESIGN

Evaluation study.

ANIMALS

25 healthy neutered ferrets (14 female and 11 male) of various ages from 2 populations (laboratory ferrets from Georgia and pet ferrets from Pennsylvania).

PROCEDURES

Each ferret underwent a physical examination and standard hematologic testing to ensure it was healthy and had clinically normal thyroid function. Once determined to be euthyroid, ferrets received a single IM injection of 100 μg of rhTSH. Blood samples were collected into plasma-separator tubes immediately before the rhTSH injection (time 0) and 4 hours after injection to measure T4 concentrations.

RESULTS

Males did not differ from females in regard to prestimulation or poststimulation plasma T4 concentrations; however, prestimulation and poststimulation T4 concentrations were significantly different between the 2 groups of ferrets. A significant difference was also identified between prestimulation T4 concentration (mean ± SD, 21.3 ± 6.1 nmol/L) and poststimulation T4 concentration (29.9 ± 8.2 nmol/L). All 25 ferrets had high poststimulation T4 concentrations (median difference, 7. 5 nmol/L; 10% to 90% interval, 3.26 to 17.70 nmol/L [0.25 to 1.38 μg/dL]; range, 2.50 to 20.70 nmol/L [0.19 to 1.61 μg/dL]); this represented a median increase in T4 concentration of 35% (10% to 90% interval, 18% to 81%; range, 8% to 126%).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that rhTSH can be used for thyrotropin stimulation testing in ferrets when administered IM. According to the findings, a euthyroid ferret should have an increase of approximately 30% in plasma T4 concentration 4 hours after rhTSH injection.

Genetic linkages for thyroxine released in response to thyrotropin stimulation in three sets of recombinant inbred mice provide evidence for shared and novel genes controlling thyroid function

BACKGROUND

Graves' hyperthyroidism is induced by immunizing mice with adenovirus expressing the human thyrotropin (TSH)-receptor. Using families of recombinant-inbred mice, we previously discovered that genetic susceptibility to induced thyroid-stimulating antibodies and hyperthyroidism are linked to loci on different chromosomes, indicating a fundamental genetic difference in thyroid sensitivity to ligand stimulation. An approach to assess thyroid sensitivity involves challenging genetically diverse lines of mice with TSH and measuring the genotype/strain-specific increase in serum thyroxine (T4).

METHODS

We investigated genetic susceptibility and genetic control of T4 stimulation by 10 mU bovine TSH in female mice of the CXB, BXH, and AXB/BXA strain families, all previously studied for induced Graves' hyperthyroidism.

RESULTS

Before TSH injection, T4 levels must be suppressed by inhibiting endogenous TSH secretion. Three daily intraperitoneal L-triiodothyronine injections efficiently suppressed serum T4 in females of 50 of 51 recombinant inbred strains. T4 stimulation by TSH was more strongly linked in CXB and BXH sets, derived from parental strains with divergent T4 stimulation, than in AXB/BXA strains generated from parents with similar TSH-induced responses. Genetic loci linked to the acute TSH-induced T4 response (hours) were not the same as those linked to induced hyperthyroidism (which develops over months).

CONCLUSIONS

Genetic susceptibility for thyroid sensitivity to TSH stimulation was distinct for three families of inbred mouse lines. These observations parallel the human situation with multiple genetic loci contributing to the same trait and different loci associated with the same trait in different ethnic groups. Of the genetic loci highlighted in mice, three overlap with, or are located up or downstream, of human TSH-controlling genes. Other studies show that human disease genes can be identified through cross-species gene mapping of evolutionary conserved processes. Consequently, our findings suggest that novel thyroid function genes may yet be revealed in humans.

Recombinant human thyrotropin in veterinary medicine: current use and future perspectives

Recombinant human thyrotropin (rhTSH) was developed after bovine thyrotropin (bTSH) was no longer commercially available. It was approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) as an aid to diagnostic follow-up of differentiated thyroid carcinoma in humans and for thyroid remnant ablation with radioiodine. In addition, rhTSH is used in human medicine to evaluate thyroid reserve capacity and to enhance radioiodine uptake in patients with metastatic thyroid cancer and multinodular goiter. Likewise, rhTSH has been used in veterinary medicine over the last decade. The most important veterinary use of rhTSH is thyroidal functional reserve testing for the diagnosis of canine hypothyroidism. Recent pilot studies performed at Ghent University in Belgium have investigated the use of rhTSH to optimize radioiodine treatment of canine thyroid carcinoma and feline hyperthyroidism. Radioiodine treatment optimization may allow a decreased therapeutic dosage of radioiodine and thus may improve radioprotection. This review outlines the current uses of rhTSH in human and veterinary medicine, emphasizing research performed in dogs and cats, as well as potential future applications.

Variable suppression of serum thyroxine in female mice of different inbred strains by triiodothyronine administered in drinking water

BACKGROUND

Recombinant-inbred mouse strains differ in their susceptibility to Graves'-like hyperthyroidism induced by immunization with adenovirus expressing the human thyrotropin (TSH) receptor. Because one genetic component contributing to this susceptibility is altered thyroid sensitivity to TSH receptor agonist stimulation, we wished to quantify thyroid responsiveness to TSH. For such studies, it is necessary to suppress endogenous TSH by administering L-3,5,3′-triiodothyronine (L-T3), with the subsequent decrease in serum thyroxine (T4) reflecting endogenous TSH suppression. Our two objectives were to assess in different inbred strains of mice (i) the extent of serum T4 suppression after L-T3 administration and (ii) the magnitude of serum T4 increase induced by TSH.

METHODS

Mice were tail-bled to establish baseline-serum T4 before L-T3 administration. We initially employed a protocol of L-T3-supplemented drinking water for 7 days. In subsequent experiments, we injected L-T3 intraperitoneally (i.p.) daily for 3 days. Mice were then injected i.p. with bovine TSH (10 mU) and euthanized 5 hours later. Serum T4 was assayed before L-T3 administration, and before and after TSH injection. In some experiments, serum T3 and estradiol were measured in pooled sera.

RESULTS

Oral L-T3 (3 or 5 µg/mL) suppressed serum T4 levels by 26%-64% in female BALB/c mice but >95% in males. T4 suppression in female B6 mice ranged from 0% to 90%. In C3H mice, L-T3 at 3 µg/mL was ineffective but 5 µg/mL achieved >80% serum T4 reduction. Unlike inbred mice, in outbred CF1 mice the same protocol was more effective: 83% in females and 100% suppression in males. The degree of T4 suppression was unrelated to baseline T4, T3, or estradiol, but was related to mouse weight and postmortem T3, with greater suppression in larger mice (outbred CF1 animals and inbred males). Among females with serum T4 suppression >80%, the increase in serum T4 after TSH injection was greater for BALB/c and C3H versus B6 mice. Moreover, the T4 increment was higher in female than in male BALB/c.

CONCLUSIONS

Our data provide important, practical information for future in vivo studies in inbred mice: we recommend that responses to TSH be performed in female animals injected with L-T3 i.p. to suppress baseline T4.

Human TSH receptor ligands as pharmacological probes with potential clinical application

The biologic role of thyroid-stimulating hormone (TSH; thyrotropin) as an activator (agonist) of the TSH receptor (TSHR) in the hypothalamic-pituitary-thyroid axis is well known and activation of TSHR by recombinant human TSH is used clinically in patients with thyroid cancer. TSHR ligands other than TSH could be used to probe TSHR biology in thyroidal and extrathyroidal tissues, and potentially be employed in patients. A number of different TSHR ligands have been reported, including TSH analogs, antibodies and small-molecule, drug-like compounds. In this review, we will provide an update on all these classes of TSHR agonists and antagonists but place emphasis on small-molecule ligands.

Diagnostic and therapeutic use of recombinant human TSH (rhTSH) in differentiated thyroid cancer

Traditionally, withdrawal of thyroid hormone to increase serum levels of thyroid-stimulating hormone (TSH) has been used in patients with differentiated thyroid carcinoma (DTC) to optimize radio-iodine uptake and serum thyroglobulin (Tg) stimulation during follow-up and in preparation for radio-iodine therapy. However, this procedure is associated with signs and symptoms of hypothyroidism which negatively affect the patient's quality of life. Recombinant human thyrotropin (rhTSH) has provided an effective alternative to thyroid hormone withdrawal. After favourable experimental trials in humans, rhTSH obtained regulatory approval in North America and in Europe as a diagnostic tool, and more recently as a preparation for radio-iodine thyroid remnant ablation. Since then, rhTSH has radically changed the diagnostic and therapeutic management of DTC patients. This review will focus on the clinical application of rhTSH in the management of DTC, highlighting current indications and future perspectives.

Evaluation of the cytogenetic effects of (131)I preceded by recombinant human thyrotropin (rhTSH) in peripheral lymphocytes of Wistar rats

The present study was carried out to investigate the cytogenetic effects of therapeutic exposure to radioiodine preceded by rhTSH in an animal model. Three groups of Wistar rats (n = 6) were used: one group was treated only with (131)I (11.1 MBq/animal); the other two groups received rhTSH (1.2 mug/rat of either Thyrogen or rhTSH-IPEN, respectively) 24 h before administration of radioiodine. The percentage of lymphocytes with chromosome aberrations and the average number of aberrations and of dicentrics per cell were determined on blood samples collected 24 h, 7 and 30 days after administration of (131)I. The data show that the treatment with radioiodine alone or associated with rhTSH resulted in a greater quantity of chromosome alterations in relation to basal values after 24 h, with a gradual decline after 7 and 30 days of treatment. An increase in chromosome alterations was also seen after rhTSH treatment alone. Neither of the treatments, i.e., with (131)I alone or associated with hormone, resulted in an aneugenic effect or influenced the kinetics of cellular proliferation in rat blood lymphocytes. There was no significant difference between the cytogenetic effects of Thyrogen and rhTSH-IPEN treatment. These data suggest that the treatment with radioiodine, associated or not with rhTSH, affects to a limited extent a relatively small number of cells although the occurrence of late stochastic effects could not be discarded.

An outline concerning the potential use of recombinant human thyrotropin for improving radioiodine therapy of multinodular goiter

Radioiodine ((131)I) treatment for nontoxic and toxic multinodular goiter (MNG) is an alternative therapeutic procedure used especially for patients with contraindication for surgery. Several studies have been conducted in recent years assessing the use of recombinant human TSH (rhTSH) in increasing (131)I uptake in MNGs. This procedure also decreases the activity level of the administered (131)I, changes the distribution of (131)I in the thyroid, lowers the absorption dose, and dramatically reduces the volume of the goiter (50-75% of the baseline volume). A major disadvantage, however, is the induction of hypothyroidism in a relatively large number of patients. A transient increase in thyroid volume and tenderness was noted in the first week of treatment. Also a short period (2-4 weeks) of hyperthyroidism was observed in most patients with potential consequences particularly for the elderly. Still, there has been no evidence to date that the adverse effects outweigh the positive results of using rhTSH. The use of rhTSH in benign goiter disease has not yet been approved worldwide, but its positive activity in MNG is remarkable and promising.

Thyroid-stimulating hormone restores bone volume, microarchitecture, and strength in aged ovariectomized rats

We show the systemic administration of low levels of TSH increases bone volume and improves bone microarchitecture and strength in aged OVX rats. TSH's actions are mediated by its inhibitory effects on RANKL-induced osteoclast formation and bone resorption coupled with stimulatory effects on osteoblast differentiation and bone formation, suggesting TSH directly affects bone remodeling in vivo.

INTRODUCTION

Thyroid-stimulating hormone (TSH) receptor haploinsufficient mice with normal circulating thyroid hormone levels have reduced bone mass, suggesting that TSH directly affects bone remodeling. We examined whether systemic TSH administration restored bone volume in aged ovariectomized (OVX) rats and influenced osteoclast formation and osteoblast differentiation in vitro.

MATERIALS AND METHODS

Sprague-Dawley rats were OVX at 6 months, and TSH therapy was started immediately after surgery (prevention mode; n = 80) or 7 mo later (restoration mode; n = 152). Hind limbs and lumbar spine BMD was measured at 2- or 4-wk intervals in vivo and ex vivo on termination at 8-16 wk. Long bones were subjected to microCT, histomorphometric, and biomechanical analyses. The direct effect of TSH was examined in osteoclast and osteoblast progenitor cultures and established rat osteosarcoma-derived osteoblastic cells. Data were analyzed by ANOVA Dunnett test.

RESULTS

In the prevention mode, low doses (0.1 and 0.3 microg) of native rat TSH prevented the progressive bone loss, and importantly, did not increase serum triiodothyroxine (T3) and thyroxine (T4) levels in aged OVX rats. In restoration mode, animals receiving 0.1 and 0.3 microg TSH had increased BMD (10-11%), trabecular bone volume (100-130%), trabecular number (25-40%), trabecular thickness (45-60%), cortical thickness (5-16%), mineral apposition and bone formation rate (200-300%), and enhanced mechanical strength of the femur (51-60%) compared with control OVX rats. In vitro studies suggest that TSH's action is mediated by its inhibitory effects on RANKL-induced osteoclast formation, as shown in hematopoietic stem cells cultivated from TSH-treated OVX rats. TSH also stimulates osteoblast differentiation, as shown by effects on alkaline phosphatase activity, osteocalcin expression, and mineralization rate.

CONCLUSIONS

These results show for the first time that systemically administered TSH prevents bone loss and restores bone mass in aged OVX rats through both antiresorptive and anabolic effects on bone remodeling.

Recombinant human thyrotropin stimulates thyroid angiogenesis in vivo

BACKGROUND

Endogenous TSH and rhTSH stimulate thyroid growth by a direct effect on thyrocytes. Our hypothesis was that rhTSH may also stimulate thyroid angiogenesis.

STUDY DESIGN

A normal human thyroid tissue sample was grafted into the epigastric area of 14 nude mice. Mice were divided in two groups of 7. The first group (treated mice) received rhTSH stimulation (0.014 UI/mouse/day for 3 weeks), while the second group (control mice) had saline. Histological study with special focus on vascular characteristics was performed by image analysis at day 21 for each graft. VEGF immunostaining score, determined by immunohistochemistry, was defined as the percentage of labeled thyrocytes score, plus an intensity score.

RESULTS

Thyroid follicles showed signs of increased colloid re-uptake activity in rhTSH group within a larger surface area than controls (p <0.01). Thyrocytes were taller in the rhTSH group (p <0.01). The diameter of capillary vessels was larger and the microvessels expansion more important in the rhTSH group (p <0.02). Relative capillary area, defined as the ratio between capillary area and follicular area, was also higher in the rhTSH group (p <0.02). VEGF immunostaining score was increased in the rhTSH group (p <0.01).

CONCLUSION

rhTSH stimulates angiogenesis and local VEGF expression in normal human thyroid.

Uses for recombinant human TSH in patients with thyroid cancer and nodular goiter

Recombinant human TSH (rhTSH) has revolutionized the care of patients with differentiated thyroid cancer. Since its approval for clinical use in 2001 in Europe (1998 in the USA), rhTSH has greatly enhanced the surveillance of these patients by allowing the avoidance of hypothyroidism for TSH stimulation. Previously, a hypothyroid state was required for TSH stimulated diagnostic whole-body radio-iodine scans (DxWBS) and thyroglobulin (Tg) levels. Patients generally prefer rhTSH as a mechanism for TSH stimulation because symptoms of hypothyroidism can be completely avoided. Currently, rhTSH is only approved for diagnostic monitoring of differentiated thyroid cancer patients. There are many other potential uses for rhTSH, including facilitation of treatment of patients with thyroid cancer and nodular goiter. The diagnostic and therapeutic role of rhTSH in patients with differentiated thyroid cancer and nodular goiter will be discussed in this review.

Recombinant human thyroid-stimulating hormone: pharmacology, clinical applications and potential uses

The major functions of pituitary thyroid-stimulating hormone (TSH) are to maintain the biosynthesis and secretion of the thyroid hormones L-thyroxine (T4) and L-3,5,3'triidothyronine (T3). The TSH core contains two apoproteins, the alpha and beta subunits. The alpha subunit is identical to that of pituitary follitropin, pituitary lutropin and placental chorionic gonadotropin, whereas the beta subunit is unique. TSH is a glycoprotein; the glycoprotein components of the alpha and beta subunits account for more than 10% of their mass and are essential for normal thyrotropic action and intravascular kinetics. The hypothalamic tripeptide, TSH-releasing hormone (TRH) is required for optimum TSH biosynthesis, particularly as far as addition of the glycoprotein components is concerned. TRH deficiency is associated with secretion of TSH molecules that are appropriately measured in most assays but have reduced bioactivity. In previous years the TSH used in clinical practice was obtained and purified from bovine pituitaries. Bovine TSH was used to test thyroid function and to augment the uptake of radioiodine in patients with thyroid cancer. Bovine TSH has been largely abandoned as a clinical agent because of adverse immune reactions. A recombinant human TSH (rhTSH; Thyrogen), has been approved by the US FDA for diagnostic use in patients with thyroid cancer. The alpha and beta subunits of Thyrogen are identical to those of human pituitary TSH. Thyrogen has a specific activity of approximately 4 IU/mg and is a potent stimulator of T4, T3 and thyroglobulin (Tg) secretion in healthy volunteers. It also increases thyroid iodide uptake in patients with thyroid cancer or multinodular goitre and in volunteers, even those exposed to large amounts of stable iodide. Thyroid cancer patients who have been treated by thyroidectomy and radioiodine ablation but are at risk of harbouring residual thyroid cancer are candidates for Thyrogen administration to prepare them for whole body iodide scans and serum Tg measurements. In thyroidectomised thyroid cancer patients who are unable to secrete pituitary TSH upon thyroid hormone withdrawal, Thyrogen is the only acceptable method to prepare them for these procedures. Thyrogen has been used on a compassionate basis to prepare patients for radioiodine ablation. rhTSH, in addition to being useful in the management of patients with thyroid cancer, is potentially useful to test thyroid reserve and to aid in thyroid-related nuclear medicine procedures. In the future, TSH analogues that have superagonist or antagonist properties may become available as therapeutic agents.

Administration of a single low dose of recombinant human thyrotropin significantly enhances thyroid radioiodide uptake in nontoxic nodular goiter

Radioiodine (131I) is increasingly used as treatment for volume reduction of nontoxic, nodular goiter. A high dose of 131I is often needed because of low thyroid radioiodide uptake (RAIU). We investigated whether pretreatment with a single, low dose of recombinant human TSH (rhTSH; Thyrogen, Genzyme Transgenics Corp.) enhances RAIU in 15 patients with nontoxic, nodular goiter (14 women and 1 man; aged 61+/-11 yr). Four patients were studied twice, and 1 patient was studied 3 times. RAIU was measured both under basal conditions and after pretreatment (im) with rhTSH, given either 2 h (0.01 mg; n = 7) or 24 h [0.01 mg (n = 7) or 0.03 mg (n = 7)] before 131I administration (20-40 microCi). Serum levels of TSH, free T4 (FT4), and total T3 were measured at 2, 5, 8, 24, 48, 72, 96, and 192 h after rhTSH administration. After administration of 0.01 mg rhTSH, serum TSH rose from 0.7+/-0.5 to a peaklevel of 4.4+/-1.1 mU/L (P < 0.0001), FT4 rose from 16.0+/-2.6 to 18.5+/-3.7 pmol/L (P < 0.0001), and T3 rose from 2.10+/-0.41 to 2.63 - 0.66 nmol/L (P < 0.0001). After administration of 0.03 mg rhTSH, TSH rose from 0.6+/-0.4 to 15.8+/-2.3 mU/L (P < 0.0001), FT4 rose from 15.2+/-1.5 to 21.7+/-2.9 pmol/L (P < 0.0001), and T3 rose from 1.90+/-0.43 to 3.19+/-0.61 nmol/L (P < 0.0001). Peak TSH levels were reached at 5-8 h and peak FT4 and T3 levels at 8-96 h after rhTSH administration. Administration of 0.01 mg rhTSH 2 h before 131I increased 24-h RAIU from 30+/-11% to 42+/-10% (P < 0.02), 0.01 mg rhTSH administered 24 h before 131I increased 24-h RAIU from 29+/-10% to 51+/-10% (P < 0.0001), and 0.03 mg rhTSH administered 24 h before 131I increased 24-h RAIU from 33+/-11% to 63+/-9% (P < 0.0001). After administration of 0.01 mg rhTSH 2 h before 131I, 24-h RAIU did not increase in 1 patient, whereas the increase in 24-h RAIU was less than 10% in 2 other patients. In contrast, administration of rhTSH 24 h before 131I increased 24-h RAIU by more than 10% in all 14 patients (by >20% in 10 and by >30% in 6). In conclusion, pretreatment with a single, low dose of rhTSH in patients with nontoxic, nodular goiter increased RAIU considerably. Our observations hold promise that administration of rhTSH before 131I therapy for nontoxic, nodular goiter will allow treatment with lower doses of 131I in these patients.