McKenzie Bioassay Research Articles

A thyroid-stimulating life: an interview with Dr. J. Maxwell McKenzie.

BEST KNOWN to the thyroid world for the introduction of the McKenzie bioassay for thyroid-stimulating antibodies (see Box), Dr. Maxwell McKenzie has had a long and distinguished career in thyroid research and internal medicine. He retired after 13 years as chairman of medicine at the University of Miami in 1994 and continues to contribute to his department and university. I persuaded Dr. McKenzie to spend some time with me in Palm Beach to talk about old times and the following is a relatively uncensored record of our conversation. Modest and retiring, Max McKenzie has much to teach us all and I have included some key references which should be read in conjunction with this transcript. This report, along with a previous interview with Dr. Robert Volpe (1), is part of an ongoing series we would like to see continued in Thyroid.

The Site of the Molecular Defect in the Thyroid Gland of thehyt/hytMouse: Abnormalities in the TSH Receptor-G Protein Complex

The hyt/hyt mouse has a severe and pervasive primary inherited hypothyroidism with significantly depressed serum T4, elevated serum and pituitary TSH, and reduced thyroid gland iodide uptake. Previous ultrastructural and histologic analysis of the hyt/hyt thyroid gland along with these biochemical abnormalities support an inherited defect in TSH responsiveness of the hyt/hyt thyroid gland. In order to evaluate the potential site of the defect in the hyt/hyt mouse, we have studied the hyt/hyt gland and hyt/hyt TSH from a biochemical and molecular standpoint. Based on demonstrated bioactivity of hyt/hyt serum in the McKenzie bioassay, this reduced responsiveness to TSH in the hyt/hyt mouse is not due to reduced bioactivity of hyt/hyt TSH or a major structural abnormality in the hyt/hyt TSH molecule. In comparison to hyt/ + euthyroid littermates and +/+ BALB/cBY progenitor strain mice, the hyt/hyt mouse demonstrates a twofold reduction in thyroid gland basal cAMP and a markedly diminished response of adenylyl cyclase to exogenous TSH. However, hyt/hyt cAMP production is equivalent to the euthyroid mice after stimulation of thyroid glands by forskolin, cholera toxin, PGE1, and isoproterenol. These results support a defect in the TSH-G protein-adenylyl cyclase system in the hyt/hyt thyroid gland. Specifically, these findings suggest that the hyt/hyt mouse has a defect in TSH responsivity due to an inherited defect in the thyroid gland TSH receptor molecule. Since the hyt/hyt gland makes T3 and T4 but at diminished levels, the proposed defect in the TSH receptor would still impart partial function. Both hyt/hyt and euthyroid hyt/ + littermates make TSH receptor mRNAs of 5500 and 2400 base pairs. This suggests that the receptor defect does not represent a major structural abnormality of the gene. The receptor defect could represent a reduction in receptor number, receptor-TSH affinity, or TSH receptor-G protein coupling. The specificity of this effect on adenylyl cyclase-cAMP is shown by the reduction of TSH-cAMP regulated thyroid peroxidase (TPO) and thyroglobulin mRNAs in the hyt/hyt thyroid gland. Given the importance of TPO and thyroglobulin in normal thyroid hormone synthesis, the reductions in TPO and thyroglobulin mRNAs in the hyt/hyt thyroid gland may underlie the significant decrease in thyroid hormone production by the hyt/hyt mouse.

Concanavalin-A, lentil, and ricin lectin affinity binding characteristics of human thyrotropin: differences in the sialylation of thyrotropin in sera of euthyroid, primary, and central hypothyroid patients.

TSH from human serum was separated into classes by serial lectin affinity chromatography using Concanavalin-A (ConA), lentil, and ricin lectins. TSH from 10 euthyroid subjects, 40 patients with primary hypothyroidism, and 1 patient with central hypothyroidism was studied. The patterns of ConA and lentil affinity binding were similar for diverse patients; forms of TSH that bound firmly to ConA also tended to bind firmly to lentil. Differences in TSH-ricin binding suggested that there were differences in the sialylation of TSH in sera of euthyroid, primary, and central hypothyroidism patients. For euthyroid subjects, 16.1 +/- 5.4% (mean +/- SD) of the TSH bound to ricin, while after neuraminidase treatment, 38.4 +/- 5.4% bound. For patients with primary hypothyroidism, 23.5 +/- 6.0% of the TSH bound to the ricin, while after neuraminidase treatment, 65.7 +/- 8.8% bound. The increase in ricin binding induced by neuraminidase treatment was significantly higher for TSH from patients with primary hypothyroidism than in that from euthyroid subjects (42.3 +/- 7.6% vs. 22.3 +/- 4.4%; P less than 0.01) and was greater for long term than for short term hypothyroid patients (49.5 +/- 5.0% vs. 36.5 +/- 6.5%; P less than 0.01). While 30% of native TSH from the serum of the patient with central hypothyroidism bound to ricin, the amount bound increased only 17.6% after neuraminidase treatment. McKenzie bioassay of pituitary-derived TSH that was similarly fractionated using ricin failed to show detectable differences in bioactivity among the lectin column fractions. Thus, 1) circulating human TSH can be consistently separated into discrete classes using serial lectin affinity chromatography; 2) there is relatively more core fucosylation of the less processed high mannose and hybrid forms of TSH and less core fucosylation of more processed complex forms; 3) ConA and lentil binding of TSH in primary and central hypothyroidism is similar to that in the euthyroid state; 4) patients with primary hypothyroidism have more sialylated TSH than a patient with central hypothyroidism or euthyroid subjects; and 5) the degree of TSH sialylation increases with prolonged primary hypothyroidism.

Effects of in vivo triiodothyronine and long acting thyroid stimulator (LATS) administration on the vitro thyroid cAMP response to thyrotrophin and LATS.

The present study was undertaken to examine the effects of prolonged in vivo treatment with T3 and long acting thyroid stimulator (LATS) on in vitro responsiveness of mouse thyroid cyclic AMP to thyrotrophin (TSH) and LATS-immunoglobulin G (IgG). In control mice, thyroid cAMP concentrations after incubation with normal-IgG (10 mg/ml) for 2 h, TSH (10 mU/ml) for 10 min and LATS-IgG (10 mg/ml) for 2 h were 1.25 +/- 0.11 (mean +/- SE) (n = 5), 15.87 +/- 3.47 (n = 6) and 2.17 +/- 0.25 pmoles/mg wet weight (n = 6), respectively. In mice given T3 (5 micrograms/ml) in drinking water for 5 days, thyroid cAMP concentrations after an incubation with TSH were reduced by 50%, as compared to those of the control mice. They were also decreased in mice injected ip with 5 mg of LATS-IgG (1000%/5 mg in the McKenzie bioassay) daily for 5 days. Combined treatment with T3 and LATS decreased the cAMP response to TSH only to the same extent as did T3 alone, indicating that the inhibitory effects of T3 and LATS were not additive. Similar findings were observed with the thyroid cAMP response to LATS-IgG in vitro; either T3 or LATS treatment in vivo decreased cAMP response to LATS-IgG in vitro, but combined treatment with T3 and LATS did not cause further inhibition as compared with T3 or LATS treatment alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of refractoriness to stimulation with long acting thyroid stimulator of thyroid hormone synthesis and thyroid hormone secretion in mice in vivo.

The present study was undertaken to examine whether long acting thyroid stimulator (LATS) induces refractoriness of thyroid hormone synthesis and thyroid hormone secretion to the stimulator in vivo. Male DDY mice fed with a low iodine diet and given 5 micrograms/ml of triiodothyronine (T3) in drinking water and libitum for 4 days were injected with 0.025 ml of LATS positive serum (1000%/0.25 ml in rhe McKenzie bioassay) ip every 24 h for 9 days. Groups of 5 mice were sacrificed before and 1, 3, 5, 7 and 9 days after the first injection of LATS for the determinations of serum thyroxine (T4) concentrations, the 1 h thyroid 131I uptake and thyroid weight. Control mice were injected with LATS negative pooled normal sera. Serum T4 concentrations elevated significantly 24 h after the 3rd injection of LATS and remained elevated until the end of the experiment. One hour thyroid 131I uptake elevated about 3-fold 24 h after the first injection of LATS. It further increased 24 h after the 3rd injection of LATS to 10-fold of the value for control animals and stayed elevated at this same level for the remainder of the study. These results indicate that stimulating effects of LATS on thyroid hormone synthesis assessed by thyroid 131I uptake and thyroid hormone secretion assessed by serum T4 concentrations were not diminished by the prior administration of the stimulator. These findings suggest that LATS does not induce refractoriness of either thyroid hormone synthesis or thy roid hormone secretion to the stimulator in mide in vivo.

Congenital Hypothyroidism Associated with Thyrotropin Unresponsiveness and Thyroid Cell Membrane Alterations

TSH stimulates thyroid functions via the TSH receptor-adenylate cyclase (AC) system. Congenital alterations of this system might be expected to result in thyroid dysfunction. This report concerns a 17-yr-old boy in whom congenital hypothyroidism was noted at the age of 18 months. The thyroid gland was not enlarged and was in a normal position, as confirmed by scintiscan. Treatment with dessicated thyroid allowed satisfactory development. The following investigations were performed 1 month after the treatment was stopped. Serum levels were: T3≤5 ng/dl; T4 ≤1 μg/dl;thyroglobulin,≤l ng/ml; and TSH, 385 μU/ml by RIA and 400 μU/ml by the McKenzie bioassay. 131I thyroidal uptake studies showed that the increase over the basal uptake was higher after dibutyryl cAMP administration (0.1 mg/kg-min for 1 h) than after TSH stimulation, which gave essentially noresponse. Light microscopy of a biopsy specimen of the isthmus obtained under local anesthesia showed a heterogeneous cellular activity; the follicles were of ...

A Comparison of Various Indicators of Murine Thyroid Stimulation by LATS

To obtain an in vitro method of LATS assay which is equally sensitive to a McKenzie bioassay, we compared the quality of cAMP generation-stimulation, thyroidal adenyl cyclase stimulation, and the stimulation of T3-release from mouse thyroid slices. Among those indicators of thyroid stimulation, stimulation by IgG of the release of T3 from incubated thyroid slices is the most sensitive, reproducible and reliable indicator, reflecting faithfully the results of a McKenzie bioassay. Stimulation of cAMP generation in slice manifested less sensitivity, but reasonable reproducibility. However, adenyl cyclase stimulation by IgG of patients with Graves' disease was erratic in two successive experiments, probably due to a non-specific effect of IgG. When adenyl cyclase stimulation was adopted as a sole indicator of thyroid stimulation, the results must be interpreted cautiously.

LATS-Protector Activity in Thyrotoxicosis Measured by Thyroidal Intracellular Colloid Droplet Formation*

A modified assay method of LATS and LATS protector (LATSP) was devised employing murine thyroidal intracellular colloid droplet formation. This method is 4- to 8-fold more sensitive to stimulators than is the regular McKenzie bioassay. For the assay of LATSP, IgG to be tested was incubated with human thyroid homogenate, then LATS-IgG was added and it was further incubated. The potency of LATS in the mixture was assayed. The adequacy of the present method for the assay of LATSP was supported by the facts that the LATSP activity was roughly related to the dose of IgG tested and that the inactivation of LATSP was observed when the IgG was pretreated with human thyroid particulate fraction and then assayed. With this method, 7 out of 32 patients with thyrotoxicosis showed LATS and 18 showed LATSP. Changes in LATSP were followed up in 7 cases out of the 18. LATSP activity decreased and then disappeared in 6 out of the 7 cases, when they had been euthyroid for a certain period of time. At 12-20 months after the treatment either by thionamide medication or by subtotal thyroidectomy. LATSP and 131I-thyroid uptake were measured in these 6 patients. In all of the 6, LATSP was negative regardless of thyroid suppressibility.

Perchlorate Ion Enhances Mouse Thyroid Responsiveness to Thyrotropin, Human Chorionic Gonadotropin and Long Acting Thyroid Stimulator

Perchlorate treatment of mice increased by 1.5-2-fold the thyroid secretory response to TSH, hCG and LATS, in the McKenzie bioassay. Perchlorate alone did not increase basal plasma radioactivity. Perchlorate augmentation of the secretory response index was roughly proportional to the level of stimulation; it was similar for all three stimulators despite their different time courses of action which were unaltered by perchlorate; it was the same whether perchlorate administration preceded, coincided with or shortly followed injection of the stimulator, a finding in keeping with the slow clearance of this ion. The perchlorate effect was dose-related, although within a narrow range (6.25-12.5 microng/mouse). Near-maximal per chlorate effect was obtained with a dose (12.5 microng) which, when tested in different experimental conditions (MMI-blocked thyroid), discharged 80% of intrathyroidal radioiodide. Perchlorate exerted its augmenting effect by enhancing thyroid secretion: it increased plasma radioiodothyronines and radioiodide concentrations without decreaseing the blood disappearance rates of iodide and iodothyronines. The potentiating effect of perchlorate probably takes place at a step prior to cyclic AMP action since it did not affect dbcAMP-stimulated secretion. The perchlorate effect may be indirect, through mobilization of minute amounts of intrathyroidal iodide.

Thyroid Function in Molar Pregnancy1

Various aspects of thyroid hormone economy were examined in 15 patients with molar pregnancy and in 5 patients with choriocarcinoma. None of the patients with molar pregnancy was clinically thyrotoxic, though serum thyroxine (T4) was increased in 13 and free T4 concentrations were above normal in four of ten in whom measurements were made. In 2 patients with elevated serum T4 levels and in one patient with normal serum T4 levels, the daily rate of T4 disposal was increase, and most of 131I derived from 131I-T4 was excreted into urine in two patients in whom estimation of urinary excretion was made. Serum total triiodothyronine (T3) concentrations closely paralleled those of serum T4, but T3/T4 ratios were lower than those previously found in patients with toxic diffuse goiter of Graves' disease. Unresponsiveness to exogenous thyrotropin-releasing hormone (TRH) was observed in 5 patients with molar pregnancy whose serum total T4 and T3 levels were increased. Human chorionic gonadotropin (hCG) concentrations in serum ranged from 0.5 to 2830 IU/ml and were less than 200 IU/ml in 36% of the patients, possibly because molar pregnancy was diagnosed by ultrasonography, rather than high titers of urinary or serum hCG. Serum thyroid stimulating activity measured by the McKenzie bioassay closely paralleled values for hCG (r:+0.94). All thyroid abnormalities disappeared quickly after removal of the mole. In choriocarcinoma, no abnormality of thyroid function was found. These results suggest that: 1) some patients with molar pregnancy display a marked elevation of serum T4, T3, and free T4 concentrations, probably as a result of the action of a thyroid stimulator which is closely related to serum hCG or may be hCG itself; 2) T4 production rates are increased in these patients, and the pituitary responds to TRH in a manner similar to that found in thyrotoxicosis. Despite this, frank clinical thyrotoxicosis is usually absent, possibly because of relatively low serum T3/T4 ratios, possibly because of the limited duration of thyroid hyperfunction, and possibly because of other factors that for the present remain unknown.

Synthesis of new cyclic nucleotides and their differential stimulatory effects on thyroid function in mice

Various 8-substituted cAMP analogues were converted into the corresponding N6,O2'-dibutyryl, N6-monobutyryl, or O2'-monobutyryl derivatives and the parent compounds as well as the new derivatives were tested for TSH-like stimulation of the thyroid function in mice in vivo by means of the McKenzie bioassay. It was found that a pronounced stimulatory effect on the thyroid secretion can be produced by certain cyclic nucleotides. The most potent compounds, 8H2N-cAMP, 8MeS-cAMP, and 8N3-cAMP at 15-30 mg/kg iv, showed an activity approximately one order of magnitude higher than that of cAMP and comparable to the action of 0.6-1.0 mU of TSH per mouse iv. Radioimmunological determination of thyroxine levels in the serum confirmed these results. Serum T4 levels in mice injected, for instance, with 8MeS-cAMP (30 mg/kg) rose from 4.85 +/- 0.25 to 6.32 +/- 0.41 mug/100 ml in 1 h, the net increase in T4 being comparable to that produced by TSH (1 mU/mouse) under identical experimental conditions. Introduction of one or two butyryl groups (in the N6 and/or O2' position) significantly increased or decreased the biological activity, dependent on the parent compound, but no direct correlation between biological activity and degree of butyrylation was apparent. The effect of these compounds on the thyroid seems to be specific for cyclic nucleotides because 8MeS-5'AMP which resembles 8MeS-cAMP but lacks the cyclic phosphate structure is inactive in the McKenzie bioassay and in the T4 radioimmunoassay.

Pituitary-Thyroid Function in Trophoblastic Disease

Pituitary-thyroid function was assessed in 12 patients with trophoblastic disease (4 hydatidiform mole, 3 invasive mole, and 5 choriocarcinoma). Thyroid-stimulating activity was detectable, by means of the McKenzie bioassay, in 6 patients (Group 1) but not in the other 6 patients (Group 2). In Group 1 serum thyrotropin (TSH) determined by radioimmunoassay was mostly undetectable and did not respond to the administration of thyrotropin-releasing hormone (TRH) determined by radioimmunoassay was mostly undetectable and did not respond to the administration of thyrotropin-releasing hormone (TRH), while in Group 2 basal TSH was detectable in half of the patients and responded to TRH in all cases. Serum concentrations of total thyroxine (T4) (18.7 +/- 2.0 mug/100 ml, mean +/- SE), free T4 (4.9 +/- 0.04 ng/100 ml), total triiodothyronine (T3) (352 +/- 72 ng/100 ml), and free T3 (0.57 +/- 0.11 ng/100 ml) in Group 1 were statistically greater than those in Group 2 (total T4, 9.2 +/- 1.0 mug/100 ml, free T4, 2.0 +/- 0.2 ng/100 ml; total T3 156 +/- 20 ng/100 ml, and free T3 0.23 +/- 0.03 ng/100 ml). Free T4 and T3 fractions were within normal limits in both groups. After treatment of 5 patients in Group 1, the thyroid stimulating activity determined by bioassay dropped to undetectable levels, the serum concentrations of thyroid hormones decreased to normal limits, and TSH response to TRH became positive. These findings indicate that an abnormal thyroid stimulator, derived from the trophoblastic tissue, stimulated the thyroid hormone secretion from the thyroid gland and in turn suppressed TSH response to TRH in some patients with trophoblastic disease.

Some factors affecting the detection of long-acting thyroid stimulator protector using the McKenzie bioassay.

SUMMARY The long-acting thyroid stimulator (LATS) protector may be detected by its property of blocking the binding of LATS to LATS absorbing activity (LAA). This study confirmed that the sensitivity of LATS protector detection was largely determined by the choice of reference mixture of LATS and LAA. Optimal sensitivity was achieved when: (a) the reference concentration of LATS activity gave a response at the upper end of the linear part of the dose–response curve; (b) the reference LATS-containing serum required a minimum of LAA for LATS binding; (c) the reference LAA preparation was free of thyroglobulin; (d) the concentration of LAA in the reference mixture was that which almost abolished the response to the reference concentration of LATS; (e) the reference LAA preparation was incubated with LATS protector before the addition of the reference LATS.

Preparation of biologically active 125I-TSH.

The present study was performed to determine whether iodinated bovine TSH of high specific radioactivity could be prepared by a method that would permit retention of its biological activity. Using stoichiometric concentrations of TSH, Nal, and chloramine T, the hormone was iodinated or radioiodinated to the extent of 1iodine atom per molecule. Iodinated TSH was then purified from the reaction mixture by sequential chromatography on Sephadex G-25 and G-100. 127I-TSH had full potency both in the TSH radioimmunoassay and in the McKenzie bioassay. I25I-TSH also had full potency in the bioassay and at least 70% of the label bound to purified bovine thyroid membranes. These studies indicate that iodinated TSH retains biological activity when prepared by the method employed, and that radioiodinated TSH prepared in this manner is a suitable tool for studying the binding of TSH to its tissue receptors. (Endocrinology95: 1228, 1974)

RELATION OF TSH CONCENTRATION IN BLOOD TO THE RADIOACTIVE RUBIDIUM 86Rb UPTAKE IN THE THYROID GLAND OF RATS: EVIDENCE OF TSH REGULATORY EFFECT ON THYROID GLAND BLOOD FLOW

ABSTRACT To study the relations between thyroid gland blood flow and the concentration of thyroid-stimulating hormone (TSH) in rats, a graded concentration of endogenous TSH was induced: for a period of 10 days, methylthiouracil was added to the food (Alkiron, Spofa, 0.2%) and in addition, in the respective groups, dried thyroid gland preparation (Thyreoidin, Spofa) in concentrations of 0.01, 0.02, 0.03, 0.04 and 0.05%. The concentration of TSH was estimated by means of the McKenzie bioassay (results are given in the percentile response index). In addition, the relative weight of the thyroid gland (in mg per 100 g of body weight) was followed and the tissue uptake of radioactive rubidium 86Rb (in % of dose per 1 g of tissue) was recorded as an indicator of changes in the thyroid gland blood flow. The experiment was repeated 3 times in exactly the same way. The course of the changes in groups fed dried thyroid from 0.01 up to 0.05 % was evaluated by means of a regression analysis. Regression lines for the same index (i. e. concentration of TSH, relative weight of the thyroid gland and uptake of 86Rb) in each particular experiment were parallel, i. e. the course of the changes for all 3 repeated experiments was identical. Regression coefficients for all the 3 indices were significantly different from zero. The values for all 3 indices then showed a statistically significant decrease concomitantly with the rising concentration of dried thyroid gland in the food, the course of the changes being very similar. Changes in the uptake of 86Rb in the thyroid gland that are in agreement with changes in the concentration of endogenous TSH are considered as further evidence of a TSH regulatory effect on the thyroid gland blood flow.

Effect of dose of thyroid hormone on the sensitivity of the McKenzie bioassay.

Florsheirn reported that large doses of thyroid hormone, when employed for suppression of intrinsic TSH in McKenzie assay mice, reduced the response of the animal to TSH or LATS. Accelerated radioiodine clearance was proposed for the mechanism of this reduction in the response. We sought to determine whether thyroidal responsiveness per se is influenced by the dose of thyroid hormone, adopting radioiodine release and intracellular colloid droplet formation as parameters of thyroid response. A daily dose of T3, 0.5, 10, 25 μg, or T4, 0.5 or 25 μg was injected SC into mice for three days after 125I injection. On the day after the last thyroid hormone injection, they received 0.075 mU TSH or LATS-IgG. Blood radioactivity and response index were obtained on the specimens taken before, 2½ or 8 hr after the injection. Colloid droplet counts were obtained on the thyroid gland removed at ½ hr after TSH or 2 hr after LATS-IgG. The dose of TSH or LATS, which caused sizable and significant extent of radioiodine rele...

Neutralizing and non-neutralizing antibodies to bovine thyroid-stimulating hormone and its subunits.

To test the possibility that the long-acting thyroid stimulator (LATS) might represent an immune complex either of thyroid-stimulating hormone (TSH) with anti-TSH or of a subunit of TSH with an appropriate antibody, we immunized rabbits with bovine TSH (bTSH), bLH (luteinizing hormone), and their alpha and beta subunits (bTSHalpha and bTSHbeta). Binding, neutralizing, and nonneutralizing antibodies were demonstrated in the antisera obtained. First, antisera to TSH, TSHbeta, and TSHalpha all bound [(125)I]TSH and [(125)I]TSHbeta. Anti-bTSHbeta antisera bound [(125)I]bTSHbeta better than did anti-TSH sera, while the binding of [(125)I]bTSH was similar with both types of antiserum. Second, the thyroid-stimulating activity (McKenzie bioassay) of TSH could be neutralized by incubation with various dilutions of anti-TSH or anti-TSHbeta. Finally, when incubation mixtures containing TSH and dilutions of anti-TSHbeta antisera that only partially neutralized TSH were treated with an antiserum against rabbit immunoglobulins to precipitate immune complexes, the bioassay response of the TSH was abolished. This phenomenon was not observed when antiserum to the intact hormone was substituted in the incubation mixture. The removal of TSH biological activity from a mixture of TSH and anti-bTSHbeta by addition of an anti-immunoglobulin indicated that biologically active immune complexes were formed between TSH and anti-TSHbeta but not between TSH and anti-TSH. The time-course of the bioactivity and several other characteristics of these complexes differentiate them from LATS.

Effect of acute exposure to cold on blood thyrotrophin (TSH) and corticosterone concentrations in the rabbit.

AbstractLeppäluoto, J., H. Lybeck, T. Ranta and P. Virkkunen. Effect of acute exposure to cold on blood thyrotrophin (TSH) and corticosterone concentrations in the rabbit. Acta physiol. scand. 1973. 89. 423–428.Rabbits were exposed to various degrees of cold and plasma TSH concentration was measured by the McKenzie bioassay method (McKenzie 1958) and plasma corticosterone by a fluoro‐metric method. After the transfer of 19 rabbits to a cold room (10o C) no consistent change (p > 0.05) in the plasma TSH level could be seen up to 3 h, whereas the plasma corticosterone level rose transiently from 6.8 to 15.8 μg/100 ml (p<0.01) at 1 h but then fell to the initial level. After immersion of anesthetized rabbits (18 cases) in ice‐cold water for 10 min, the colonic temperature fell from 38 to 30o C. By 2 h plasma TSH levels were again unchanged (p > 0.05) and plasma corticosterone levels had risen from 5.9 to 27.4 μg/100 ml (p < 0.001, 10 cases), or were unchanged (p > 0.05) but high i nanimals pretreated with stereotactically around the preoptic area provoked a decrease in hypothalamic temperature by 3o C (8 cases), while plasma TSH fell to an undetectable level adn corticosterone rose from 18.7 to 26.2 (p < 0.05) μg/100 ml. We conclude that in the rabbit the hypothalamus is refractory to cold stimulus, possibly through a mechanism associated with the secretion of ACTH.

Is TSH-Stimulated Thyroid Hormone Release Inhibited by Iodide?1

The effect of iodide on TSH-stimulated thyroid hormone release in the McKenzie bioassay was studied. When mice were given KI (0.01 or 10 mg/ml in drinking water) for 24 hr before TSH, thyroid 125I release in response to TSH expressed as the percent increase in serum 125I (2 hr value/0 hr value) was significantly inhibited, an effect in good agreement with previously reported results. However, the absolute increase in serum 125I (2 hr value-0 hr value) was not changed by Kl-treatment. In Kl-treated mice, the concentration of 125I present in the serum before TSH injection was significantly higher than that in the control mice. Methimazole (0.02 mg/ml in drinking water) abolished the inhibitory effect of iodide on the percent increase in serum 125I in response to TSH by abolishing the increase in the concentration of serum 125I before TSH. Changes in serum 125I-PBI were essentially the same as those in serum 125I. These results suggest that 1) the inhibitory effect of iodide on the percent increase in serum ...

Induction of a LATS—like Response by Thyroglobulin in the McKenzie Assay System

In a modified McKenzie bioassay system, significant, and sometimes striking, stimulatory activity resembling that of LATS was induced by soluble supernatants of bovine thyroid tissue, by purified bovine thyroglobulin (TG), either obtained commercially or freshly-prepared by DEAE cellulose chromatography, and by the soluble supernatant of a human thyroid gland. Stimulatory activity, as evidenced by an increase in blood 131I, was manifest at 2 hr after administration of TG and was maximum between 11 and 20 hr. Varying doses of TG elicited a typical log dose—response curve, the minimum effective dose being 0.1 mg. As indicated by direct analysis, increased blood radioactivity elicited by TG was comprised mainly of 131I—thyroxine. The effect of TG could not be explained by a retarded disappearance of 131I—thyroxine from the blood, since very large doses of TG failed to retard the disappearance of exogenous labeled hormone. (Endocrinology 92: 1538, 1973)