Effects of various modes of androgen substitution therapy on erythropoiesis

In order to investigate differential effects of androgens on erythropoiesis, 55 men with clincally and biochemical confirmed hypogonadism were randomly assigned to 4 groups receiving different forms of androgen substitution: Mesterolone (MES) 100 mg/d, testosterone undecanoate (TU) 160 mg/d, testosterone enanthate (TE) 250 mg i.m./21 days or 1200 mg crystalline testosterone (TPEL) subcutaneously implanted at study begin. Previous testosterone medication had been suspended at least 3 months prior to study begin. Testosterone (T), dihydrotestosterone (DHT), hemoglobin (HB) and hematocrit (HC) were assessed before, during and after substitution of androgens. MES did not increase serum T and TU raised average T levels during substitution to 5.7 +/- 0.3 nmol/l, thereby doubling baseline concentrations. TE resulted in a 6fold increase of baseline T yielding 13.5 +/- 0.7 nmol/l and TPEL increased serum T 8.5fold to 23.2 +/- 1.1 nmol/l. Average DHT levels during substitution were 4.3 +/- 0.2 (MES), 3.3 +/- 0.2 (TU), 4.0 +/- 0.4 (TE) and 5.5 +/- 0.4 (TPEL) nmol/l. The groups receiving TPEL, TU or TE showed a significant rise of HB and HC compared to baseline, whereas in the MES group these parameters did not change significantly. MES increased HB by 5.6 +/- 1.8 g/l, TU by 12.7 +/- 2.8 g/l, TE by 21.1 +/- 2.6 g/l and TPEL by 21.7 +/- 4.0 g/l. HC was raised by 1.8 +/- 0. 4% in the MES group, 3.9 +/- 1.1% in the TU group and 6.4 +/- 0.9% and 6.5 +/- 1.6% in the TE and TPEL groups, respectively. Except for 1 subject in the TPEL group, the HB and HC stayed within the normal limits. We conclude that, T, but not DHT, stimulates erythropoiesis in a dose dependent manner. T levels within the low normal range for men are required for maximal stimulation of erythropoiesis.

Significant changes in thyroid hormone parameters after a four week recreation period at the North Sea without alterations of iodine intake

Many studies have been carried out evaluating thyroid hormone parameters in patients suffering from various illnessess. However data on thyroid function after a recreation period are missing. Therefore we evaluated thyroid hormone parameters in 178 patients (mostly suffering from chronic obstructive lung disease) undergoing a four week recreation period in a health spa on the island Borkum at the North Sea. We observed a subtle, but significant increase in basal TSH concentrations from 1.20 mU/l (median) to 1.50 mU/l; (p<0. 001) and a fall in T4 values from 97.5 +/- 17.7 nmol/l (mean +/- SD) to 90.3 +/- 17.0 (p<0.001) and T3 from 2.21 +/- 0.33 nmol/l to 2.09 +/- 0.33 (p<0.001). However no increase in iodine intake occurred during the four weeks: median iodine excretion 61 microg iodine/g creatinine at the beginning vs 65 microg iodine/g creatinine at the end.

IN CONCLUSION

a recreation period at the North Sea is associated with subtle but significant changes in thyroid hormone parameters. However no increase in iodine intake occurs during the four week observation period.

Triiodothyronine (T3) reflects renal graft function after renal transplantation

OBJECTIVE

Abnormalities in thyroid function are observed in patients with end stage renal disease. However, there are no data available evaluating sequential changes of thyroid function after renal transplantation. Therefore, we have studied thyroid hormone function in the immediate post-operative period after renal transplantation in order to determine the relationship between improving renal function and changes in thyroid hormone economy.

DESIGN AND PATIENTS

Thyroid function was evaluated in 22 patients before and on days 1, 3, 7 and 15 after renal transplantation. All patients received prednisone and cyclosporin as immunosuppressive therapy. Twelve patients with normal renal function undergoing comparable surgical procedures served as a control group.

MEASUREMENTS

Serum creatinine and thyroid hormone parameters (total T4, total T3, free T4, free T3, thyroxin binding globulin (TBG), reverse T3, T3 sulphate and TSH) were measured.

RESULTS

According to post-operative kidney function after renal transplantation, patients could be subdivided into three groups: five patients had primary graft function (group I); seven patients had delayed graft function because of acute renal failure (group II); 10 patients had delayed graft function requiring high doses of prednisone and some also of OKT3 because of acute rejection (group III). There was a significant fall in T3 and T4 concentrations with a concomitant rise in reverse T3 in all patients up to 3 days after renal transplantation. However, only patients in group I reached pre-operative values on day 15 after renal transplantation (serum creatinine 167 +/- 52 microM), whereas patients in group II (creatinine 609 +/- 118 microM) and group III (creatinine 839 +/- 71 microM) continued to have T3 concentrations well in the hypothyroid range (group I, 1.68 +/- 0.28 nM) vs 0.87 +/- 0.09 nM in group II and 0.76 +/- 0.10 nM in group III; P < 0.01). Serum T4 concentrations were also low in group III (47.7 nM vs 100.2 nM in group I; P < 0.05) 15 days after renal transplantation. These changes were accompanied by a concomitant fall in T3/TBG ratio and in free T3. Elevated reverse T3 returned to normal values in all groups on the 15th day after renal transplantation. TSH fell significantly on the first post-operative day, but did not return to pre-operative values in renal transplantation patients. In the control group, TSH did not change during the study period. T3 sulphate, known to be elevated in chronic renal failure, remained above normal in all patients irrespective of graft function during this study period.

CONCLUSIONS

T3 concentrations reflect renal graft function after renal transplantation. T3 is below normal in patients with delayed graft function (acute renal failure or acute rejection). The post-operative period (up to 3 days after renal transplantation) is associated with a low T3 syndrome. TSH does not return to pre-operative values even in patients with primary graft function. This might be due to the administration of prednisone. T3-sulphate is elevated before and after renal transplantation irrespective of graft function.

Beta-human choriogonadotropin therapy and HIV-related Kaposi's sarcoma

Recently, two clinical trials demonstrated an antitumour effect of systemic high-dose beta-hCG therapy and of different regimens of local beta-hCG injections in AIDS-related Kaposi's sarcoma. We report the efficacy and safety of subcutaneous beta-hCG treatment (low-dose (2500-25000 IU/day) or high dose (25000-100000 IU/day)) in eight patients with advanced HIV disease in whom systemic chemotherapy and radiation were contraindicated or had failed. During therapy, serum hCG-concentrations as well as LH and FSH were measured. In the low-dose regimen one partial response was achieved. In the high-dose regimen, one patient maintained his response without further improvement. Three patients had stable disease and four patients disease progression. Serious side effects related to beta-hCG therapy were not observed. In conclusion, systemic beta-hCG-therapy for Kaposi's sarcoma is safe but associated with regression only in a minority of patients with advanced HIV-disease.

Influence of coronary artery bypass surgery on thyroid hormone parameters

The postoperative period after cardiac surgery with cardiopulmonary bypass (CPB) is associated with a low T3 syndrome, i.e. low T3 and fT3 concentrations in the presence of normal T4 and TSH concentrations. So far, results from studies evaluating thyroid function during and after CPB are rather conflicting. We therefore evaluated prospectively thyroid function in 28 patients before, during and up to 3 days after coronary artery bypass surgery. We could demonstrate the most significant changes in thyroid hormone concentrations on day 1 after CPB (low T3 and fT3 concentrations, elevated rT3 concentrations in the presence of a significant fall of TSH). T3 fell from 1.93 to 0.6 nmol/1 and fT3 from 5.5 to 1.42 pmol/1. Those patients with low cardiac output syndrome after surgery had significantly lower T3 concentrations than patients without this complication. Moreover, those patients, who already had significant lower T3 values prior to CPB, also demonstrated low T3 concentrations on day 1 after CPB. Cortisol usually has a suppressive effect on TSH secretion. However, the effect of cortisol on TSH in patients undergoing CPB seems to be not that important: those patients with high endogenous cortisol concentrations on day 1 after CPB had similar TSH values to those patients with only slightly elevated cortisol concentrations. Also, the application of high doses of catecholamines seems to have only minor effects on TSH secretion, because those patients requiring high doses of dopamine over a prolonged time period had essentially the same TSH values after CPB. Patients who had been exposed preoperatively to high doses of iodine did not demonstrate significantly different thyroid hormone concentrations.

IN CONCLUSION

We could demonstrate that CPB induces a low T3 syndrome up to 3 days after surgery. Those patients with low T3 concentrations prior to surgery demonstrate postoperatively a more severe degree of nonthyroidal illness (NTI). Catecholamines and cortisol seem to have only minor effects on the TSH secretion after CPB. The influence of a previous iodine contamination is negligible.

Skeletal immaturity, IGF-I and IGFBP-3 serum concentrations in Legg-Calvé-Perthes disease (skeletal immaturity, IGF-I and IGFBP-3 in LCPD)

BACKGROUND

Skeletal immaturity is a major feature in Legg-Calvé-Perthes disease (LCPD). Evaluation of growth hormone concentration, somatomedin activity, or insulin-like growth factor I (IGF-I) concentration revealed inconsistent results. Recently, IGF-binding protein 3 (IGFBP-3) was found normal in relation to chronological age in LCPD patients.

PATIENTS

In this study IGF-I and IGFBP-3 were measured in the serum of 23 children with unilateral LCPD and in 23 sex and age matched controls.

METHODS

IGF-I and IGFBP-3 were measured with radioimmunoassays, using an IGF binding site-blocked assay for IGF-I. The results were related to the chronological age in all and to the bone age in 19 of the patients.

RESULTS

Bone age was retarded in 16 of 19 patients with a delay of one year or more in twelve children (mean 14.75, range 2-35 months). Chronological age and bone age related IGF-I and IGFBP-3 serum concentrations were predominantly within the normal ranges and did not differ significantly from the matched controls. IGF-I and IGFBP-3 serum levels showed a high correlation, which was similar in LCPD (r = 0.7; p < 0.0001) and in the control group (r = 0.8; p < 0.0001).

CONCLUSIONS

Our data confirm that most children with LCPD are skeletally immature. However, IGF-I measured with IGF-II-blocked IGFBP binding sites, and IGFBP-3 serum concentrations analysed with respect to bone age show no evidence for a disturbance of the hypothalamo-pituitary-somatomedin axis in these children.

Pharmacokinetics and pharmacodynamics of subcutaneous testosterone implants in hypogonadal men

OBJECTIVE

There are advantages and disadvantages with all of the presently available types of testosterone replacement for hypogonadal men. We performed this investigation to establish detailed data about the pharmacokinetics, pharmacodynamics, feasibility and side-effects of subcutaneously implanted testosterone (T) pellets.

DESIGN AND MEASUREMENT

In a single-dose, open-label, non-randomized study, 6 T-pellets, each containing 200 mg of fused crystalline T, were implanted in the subdermal fat tissue of the lower abdominal wall of 14 hypogonadal men. Blood samples for determination of T, LH, FSH, 5 alpha-dihydrotestosterone (DHT), sex hormone binding globulin (SHBG) and oestradiol (E2) were obtained at 0, 0.5, 1, 2, 4, 8, 12, 24, 36, 48 hours and on day 21 after implantation and then every 3 weeks until day 189, and on days 246 and 300 during follow-up. In another 36 hypogonadal men the feasibility and side-effects of T-pellets were evaluated.

PATIENTS

Fourteen patients participated in the detailed pharmacokinetic study and another 36 patients in the assessment of feasibility and side-effects. All patients (age range 18-61 years) suffered from primary or secondary hypogonadism (T < 3.6 nmol/l).

RESULTS

The pharmacokinetic study in 14 hypogonadal men revealed an initial short-lived burst release of T with a peak concentration of 49.0 +/- 3.7 nmol/l at 0.5 +/- 0.13 days which was followed by a stable plateau lasting until day 63 (day 2, 35.2 +/- 2.3; day 63, 34.8 +/- 2.6 nmol/l). Thereafter serum T gradually declined and was close to baseline concentrations on day 300. Apparent terminal elimination half-life (t1/2) was 70.8 +/- 10.7 days and apparent mean residence time 87.0 +/- 4.5 days. On average, serum T was below 10 nmol/l after 180 days. Absorption of T followed a zero-order release kinetic with an absorption half-time of 74.7 days (95% confidence interval: 71.1-78.5) and was almost complete by day 189 (95.9 +/- 0.84%). Serum DHT and E2 were significantly elevated from day 21 to day 105 and correlated significantly with T (DHT, r = 0.65, P < 0.0001, E2, r = 0.67, P < 0.0001). SHBG was significantly decreased from day 21 to day 168. In 6 men with primary hypogonadism T suppressed LH and FSH to the eugonadal range from day 21 to 126 and 42 to 105, respectively, with nadirs occurring at day 84 (LH) and day 63 (FSH). LH and FSH were highly inversely correlated with T (r = -0.47 and -0.57). The only side-effect observed during 112 implantations in the total group of 50 men were 6 local infections (5.4%) leading to extrusion of 5 pellets in 3 men. When given the choice, all patients except one preferred T-pellets to their previous T medication for permanent substitution therapy.

CONCLUSION

T-pellets are the androgen formulation with the longest biological action and strongest pharmacodynamic efficacy in terms of gonadotrophin suppression. The pharmacokinetic features are advantageous compared to other T preparations and the patient acceptance is high.

[Influence of non-diabetic pregnancy on fructosamine and HbA1c concentration]

HbAIc and fructosamine concentrations were measured in the course of 177 nondiabetic pregnancies and compared with the corresponding values of 24 nondiabetic nonpregnant women. In all three trimesters HbAIc and fructosamine were significantly lower than the corresponding values in the nonpregnant women; HbAIc: 1st trimester 4.77 +/- 0.62%, 2nd trimester 4.38 +/- 0.59%, 3rd trimester 4.33 +/- 0.49%, p < 0.01; fructosamine 1st trimester 2.13 +/- 0.17 mmol/l, 2nd trimester 2.02 +/- 0.15 mmol/l, 3rd trimester 1.90 +/- 0.15 mmol/l, p < 0.01; nonpregnant women: HbAIc 5.13 +/- 0.41%, fructosamine 2.53 +/- 0.17 mmol/l. However, if the fructosamine is correlated to the respective total protein concentration a constant value results for the course of pregnancy. The changes in the HbAIc and fructosamine concentrations in pregnancy should be taken into account when treating pregnant diabetics.

Effect of small doses of iodine on thyroid function during caloric restriction in normal subjects

It is well recognized that starvation and malnutrition are associated with a low-T3 syndrome in man. A similar condition has been observed after intake of a low carbohydrate hypocaloric diet. However, little is known about the influence of iodine on these conditions. Therefore, we evaluated the effect of iodine supplementation on thyroid function before and after a short-term intake of a low carbohydrate diet in normal subjects residing in an iodine-deficient area. The study was performed in 16 young euthyroid, nonobese volunteers (11 males, 5 females). The subjects were placed on a low carbohydrate (800 kcal) diet for 4 days. Eight subjects received 500 micrograms iodine (oral) daily beginning 4 weeks before diet. The control group (n = 8) received no iodine. After iodine supplementation, iodine excretion increased from 52 to 405 micrograms iodine/g of creatinine. Total T4 showed a slight but significant increase (104.2 nmol/l vs. 115.8 micrograms/dl; p < 0.001); fT4 was unchanged. The intake of the hypocaloric low carbohydrate diet resulted in a striking decrease in both total and free T3 and an increase of rT3 irrespective of iodine supplementation. T4 and fT4 were not affected in either group. During diet, iodine administration resulted in a decrease of basal TSH from 2.3 to 1.2 mU/l (p < 0.05), delta TSH from 10.3 to 4.5 mU/l (p < 0.01) and delta T3 (T3 180 min after TRH) from 0.7 to 0.3 nmol/l (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Conservative and surgical management of incidentally discovered adrenal tumors (incidentalomas)

Of 50 patients with incidentalomas (INC), 18 were adrenalectomized and in 18 patients the INC was left in place. For 14 patients clinical data were insufficient for evaluation. Follow-up investigation of the 18 unoperated subjects 11-101 months (median 32.2) after the diagnosis had been made revealed unchanged size of the INC [initially 2.1 +/- 0.8 cm (mean +/- SD) at follow-up 2.0 +/- 1.0 cm]. Cushing's syndrome developed in one patient, which was not evident at the initial discovery of the INC 32 months before. "Pre-Cushing's Syndrome" was detected in 1 patient and confirmed in a second who had displayed a pathologically high dose dexamethasone suppression test 101 months before. In addition, 3 male patients with a hitherto unknown mild subclinical defect of 21-hydroxylase activity were identified. The remaining 12 patients had normal endocrine activity of their adrenals. Eighteen patients were adrenalectomized with an average tumor size of 3.96 +/- 1.88 cm. Histologically, 10 (52%) adenomas were observed, including 3 with signs of hypercortisolism. Adrenal hyperplasias were observed in 2 patients, metastasis in 1 patient. 31.5% of the INC which were removed were nonmalignant tumors of other than adrenal origin. We conclude that initially endocrinologically inactive adrenal tumors can eventually develop autonomous endocrine activity and therefore need to be reexamined at regular intervals. Conservative management with regular follow-up investigations is the preferable treatment for small incidentalomas when endocrine over-activity has been excluded and no indications of malignancy exist. Based on these observations and the literature a diagnostic and therapeutic strategy is presented.

Variable prevalence of lymphocytic thyroiditis among diabetes-prone sublines of BB/W or rats

The BB/Wor rat develops spontaneous autoimmune insulin-dependent diabetes mellitus (DM) and lymphocytic thyroiditis (LT). Six different inbred sublines of this rat model have been selected for studying the pathogenesis of DM and, thereby, the prevalence of DM has been carefully monitored and found to be relatively constant. In contrast, we have observed a striking difference in the prevalence and intensity of LT in these six sublines, varying from 100% in NB subline rats to 4.9% in BE subline rats at 105-110 days of age. Excess iodide administration frequently increases the prevalence of LT but did not do so in the two sublines (BB and BE) with the lowest frequency of spontaneous LT. In view of this variable prevalence of LT in the different BB/Wor sublines, it is imperative that investigators studying the pathogenesis and modulation of LT in this rat model select those sublines which express a desired frequency of spontaneous LT.

TSH secretion in Cushing's syndrome: relation to glucocorticoid excess, diabetes, goitre, and the 'sick euthyroid syndrome'

Thyrotrophin (TSH) secretion was studied in 63 patients with Cushing's syndrome (53 patients with pituitary dependent Cushing's disease, eight with adrenocortical tumours, and two with the ectopic ACTH syndrome). Prior to treatment, TSH response to 200 micrograms of TRH intravenously was significantly decreased compared to controls; TSH response was 'flat' (increment less than 2 mU/l) in 34 patients (54%). Patients with a flat response to TRH had significantly higher morning and midnight cortisol levels than patients with a TSH response of 2 mU/l and more; this was not due to differences in serum thyroid hormone levels. Basal TSH, TSH increment after TRH, and stimulated TSH value, but not serum triiodothyronine, were correlated with cortisol measurements (0800 h serum cortisol, midnight cortisol, and urinary free corticoid excretion). After exclusion of 40 patients with additional disease (severe systemic disease, diabetes mellitus, or goitre), cortisol-TSH correlations were even more pronounced (r = -0.73 for midnight cortisol and stimulated TSH levels), while in the patients with additional complications, these correlations were slight or absent. Successful treatment in 20 patients was associated with a rise in thyroid hormone levels and the TSH response to TRH. These results indicate that (1) the corticoid excess but not serum T3 is the principal factor regulating TSH secretion in Cushing's syndrome, (2) a totally flat response to TRH is rare, and (3) TSH suppression and lower than normal serum thyroid hormone levels are reversible after treatment. Since factors like severe systemic disease, diabetes mellitus and goitre also affect TSH secretion, they tend to obscure the statistically significant correlations between cortisol excess and TSH secretion.

Effect of thalidomide on the incidence of iodine-induced and spontaneous lymphocytic thyroiditis and spontaneous diabetes mellitus in the BB/Wor rat

Thalidomide, a derivative of glutamic acid, has immunosuppressive effects and suppresses graft-vs-host disease in the rat and following bone marrow transplantation in man. It is effectively used in the treatment of erythema nodosum leprosum and has a potential therapeutic effect in a variety of autoimmune diseases. In view of these observations, we evaluated the effect of thalidomide on the incidence of spontaneous and iodine-induced lymphocytic thyroiditis and spontaneous insulin dependent diabetes mellitus in the BB/Wor rat. Thalidomide did not suppress the incidence of lymphocytic thyroiditis and serum anti-thyroglobulin antibodies or affect the serum concentrations of T4, T3 and TSH in this rat model. Thalidomide also did not affect the incidence of insulin dependent diabetes mellitus. In contrast to preliminary studies in man and rat demonstrating efficacy in the therapy of autoimmune diseases, thalidomide did not prevent or suppress autoimmune lymphocytic thyroiditis or insulin-dependent diabetes mellitus in the BB/Wor rat.

The inhibitory effect of large doses of methimazole on iodine induced lymphocytic thyroiditis and serum anti-thyroglobulin antibody titers in BB/Wor rats

The BB/Wor rat spontaneously develops autoimmune insulin dependent diabetes mellitus and lymphocytic thyroiditis (LT). Excess iodine ingestion enhances and low iodine diet decreases the incidence of LT in this rat model but does not affect the incidence of diabetes mellitus. The administration of a low dose of methimazole (MMI; 870 ng/gm bw ip daily) from 30-90 days of age had no significant effect on thyroid function or on the incidence of iodine induced LT and serum anti-thyroglobulin (Tg) antibodies measured by an ELISA assay. A large dose of MMI (0.05% in the drinking water) induced goiter and hypothyroidism. In addition, the incidence of LT was markedly attenuated (76% vs 6%, p less than 0.001) and reduced titers of serum anti-Tg antibodies (0.59 +/- 0.1 OD vs 0.08 +/- 0.01, p less than 0.001) were observed. This inhibitory effect of MMI on the occurrence of iodine induced LT in the BB/Wor rat may be due to the lower antigenicity of the poorly iodinated Tg secondary to MMI therapy and/or to an immunosuppressant effect of MMI itself.

Effect of L-thyroxine administration on the incidence of iodine induced and spontaneous lymphocytic thyroiditis in the BB/Wor rat

Chronic L-thyroxine administration (6 micrograms/100g BW, ip, daily) for 2 or 3 months suppressed serum TSH concentrations and decreased both the incidence of spontaneous lymphocytic thyroiditis (LT) and the serum levels of anti-thyroglobulin (anti-Tg) antibodies in the diabetes prone BB/Wor rat. This suggests that TSH may play a role in the occurrence of LT in this rat model. In contrast to these observations, L-thyroxine administration did not affect the markedly increased incidence of LT or the elevated serum anti-Tg antibodies in iodine supplemented BB/Wor rats, suggesting that TSH stimulation is not necessary for the development of iodine induced LT in this rat model. Other factors, such as the increased antigenicity of highly iodinated Tg, may be more important.

Effect of mouth rinsing with two polyvinylpyrrolidone-iodine mixtures on iodine absorption and thyroid function

A prospective study was conducted to investigate the effect of long term therapy with two iodine-containing mouth rinses on thyroid function. Two groups of subjects were treated daily for 6 months with either a 5% polyvinylpyrrolidone (PVPI)-1.5% H2O2 mixture (Perimed) or a 5% PVPI-water mixture. Thyroid function studies, serum iodine concentrations, and urinary iodine excretion were measured before treatment, at 6-week intervals during the 6-month treatment period, and 3 weeks after the last treatment. There was evidence of significant iodine absorption (elevated serum total iodine and inorganic iodide concentrations and urinary iodine excretion) from daily use of both Perimed and the PVPI-water mixture. Serum T3 and T4 concentrations and the free T4 index did not change. There was a small significant rise in serum TSH concentrations during mouth rinse therapy, but all values remained within the normal range. This small increase in serum TSH is a normal adaptive response to the antithyroid effect of increased iodine intake and accounts for the maintenance of normal serum T4 and T3 concentrations. While daily use of these iodine-containing mouth rinses does result in significant iodine absorption, there is no evidence for the development of thyroid dysfunction during a 6-month course of therapy.

Effect of iodine intake and methimazole on lymphocytic thyroiditis in the BB/W rat

Spontaneous LT and elevated serum anti-Tg occur in the diabetes prone BB/W rat, but thyroid function is essentially normal in the rats with LT. Prolonged low dose MMI decreases the incidence of LT in BB/W rats. The administration of excess iodine beginning at 30 days of age markedly accelerates the occurrence of LT and anti-Tg at 90 days of age. Low iodine intake decreases the incidence of LT. Excess iodine intake did not induce LT in W-line, Wistar-Furth, and Sprague-Dawley rats. This suggests that iodine induced LT occurs only in genetically susceptible rats. Despite the increased incidence of LT during iodine administration, thyroid function remains essentially normal. This is in contrast to the frequent induction of hypothyroidism following iodine administration to euthyroid patients with Hashimoto's thyroiditis. In order to decrease thyroid reserve, rats were hemi-TX at 30 days of age. The administration of iodine markedly increased the incidence of LT and serum anti-Tg, increased the weight of the remaining lobe, and induced hypothyroidism as determined by significantly lower serum T4 and T3 concentrations and elevated serum TSH concentrations. Excess iodine administration to hemi-TX W-line rats (genetically equivalent, non-diabetes, non-LT prone BB/W rats) did not induce LT but did induce hypothyroidism, suggesting that BB/W and W-line rats are susceptible to iodine induced hypothyroidism, perhaps unrelated to the induction of LT. Excess iodine did not induce LT or affect thyroid function in hemi-TX Wistar-Furth and Sprague-Dawley rats.