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D van der Heide

Publications and source records attributed to D van der Heide.

At least 55 records · Page 3Linked to original sources
PubMed1988

Thyrotropin (TSH) receptor modulation by specific TSH receptor antibodies in Graves' disease.

In Graves' disease (GD), an antireceptor autoantibody disease, individual variability in the pathogenic interaction between TSH receptors and autoantibodies has been reported. This variability can be due to allotypic (person to person) variability in the receptors or differences in autoantibody amount or specificity. This fundamental issue was investigated by evaluating immunoglobulin G (Ig)-induced TSH receptor modulation in thyroid tissue from 19 patients with GD. TSH receptor modulation by Graves' Ig was defined as the appearance of 1 class of high affinity binding sites, instead of the usual 2 classes of binding sites. Ig-induced modulation of receptors occurred in 9 of 19 (47%) experiments with autologous (patient's own) tissues and correlated with the presence of TSH receptor antibodies, measured as TSH binding inhibitor Igs. Of these 9 receptor-modulating Graves' Ig preparations, 7 (78%) also had a receptor-modulating effect in other patient's (homologous) thyroid tissue. Nine of the 10 Graves' Ig preparations that were negative for TSH receptor-modulating activity in autologous thyroid tissue were tested with other patients' thyroid tissues; 7 (78%) were negative, and all were TSH binding inhibitor Ig negative. We conclude that variability in the occurrence of TSH receptor modulation was associated with the presence or absence of TSH-binding inhibitor Ig. No evidence for allotypic differences in TSH receptors in GD was found.

Adolescent↗
PubMed1986

Thyroid-stimulating immunoglobulins and thyroid function tests in two siblings with neonatal thyrotoxicosis.

Thyroid function and serum TSI levels in two siblings with neonatal thyrotoxicosis are described. The first infant was treated with exchange transfusion and potassium iodide. The second infant was treated with intrauterine propylthiouracil followed by potassium iodide. In contrast to the first infant, the second infant had no clinical sign of neonatal thyrotoxicosis. He also had lower TSI levels with a biological half-life of 5 days. Only one of three assays showed some TSI activity in breast milk.

Adult↗
PubMed1986

Circadian urinary excretion rhythms in adrenalectomized rats.

The impact of the adrenal system on urinary rhythms was investigated in adrenalectomized (ADX) rats under various experimental conditions. During a 12:12 light-dark cycle the acrophases were shifted in ADX rats with respect to control rats. Under constant light conditions ADX rats displayed free-running rhythms, similar to those of control rats. The periods were stable in blind rats but not in rats maintained on a constant light cycle. The abrupt change in period, which occurred after approximately 8 days, suggests a stage of internal desynchronization. A 6-h delay in the administration of corticosterone to ADX rats caused a delay shift of the acrophases. A single intraperitoneal injection of corticosterone in blind free-running ADX rats caused delay or advance shifts so that we could construct phase-response curves for the various excretory rhythms. These observations indicate that the adrenals are not essential for the establishment of the urinary rhythms; however, corticosterone influences the phase setting of these rhythms. The site of action is probably the X pacemaker (controlling the body temperature rhythm), although we cannot totally exclude an additional effect on secondary (renal) oscillators.

Adrenalectomy↗
PubMed1986

Conversion of thyroxine to 3,5,3'-triiodothyronine in several rat tissues in vivo: the effect of hypothyroidism.

The local conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) has been recognized as a source of T3 at various sites in euthyroid rats. The present study was designed to evaluate the effect of hypothyroidism on the source and quantity of T3 at several of these sites (liver, cerebral cortex (Cx), thymus, testis, brown adipose tissue). For this purpose intact euthyroid rats and radiothyroidectomized (RTx) rats received a continuous iv infusion of [125I]T4 and [131I]T3 until isotopic equilibrium was attained. In addition to the labelled iodothyronines, RTx rats received a continuous iv infusion of 0.75 microgram T4/day, in order to maintain a defined hypothyroid state. At the end of the infusion period the animals were bled and perfused, and homogenates of the various organs were prepared. The mean plasma T4 and T3 levels in T4-maintained RTx rats, as measured by RIA, were 1.5 micrograms/dl and 15 ng/dl (euthyroid values: 5.2 micrograms/dl and 48 ng/dl, respectively). The plasma and tissue homogenates were processed for thin layer chromatography and the [125I]T4, [125I]T3 and [131I]T3 levels determined. From these data the concentrations of T4, total T3 and T3 derived from local T4 to T3 conversion (LcT3(T4)) in tissue could be calculated. The relative mean contribution of LcT3(T4) to the total T3 in Cx (75%), thymus (31%), testis (43%) and brown adipose tissue (65%) from hypothyroid rats was higher than that determined for euthyroid animals (66%, 19%, 29% and 27%, respectively). The reverse was found for the liver (15% vs 39%).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Resynchronization patterns for urinary rhythms in rats after light-dark shifts.

Diurnal urinary rhythms during a fixed 12:12 light-dark cycle were studied in male and female rats. After a control period of 9 days the light-dark cycle was shifted either +6 or -6 h by delaying or advancing the light period, respectively. Subsequently the resynchronization process was studied for 19-21 days. In both male and female rats an asymmetry effect was present: resynchronization was more rapid after a -6-h shift than after a +6-h shift. However, female rats exhibited a rate of resynchronization slower than male rats. During the process of resynchronization a state of transient internal dissociation was found for all urinary constituents. These results probably point to different control systems rather than to different circadian pacemakers. Further analysis of the role of sex steroid hormones is required in view of the sex variations reported.

Adaptation, Physiological↗
PubMed1985

Concentrations of thyroxine and 3,5,3'-triiodothyronine at 34 different sites in euthyroid rats as determined by an isotopic equilibrium technique.

The present study was designed to assess the quantities of T4 and T3, and the source (i.e. plasma-derived vs. locally produced) of the latter iodothyronine, in various rat tissues. For this purpose, normal intact rats were brought to isotopic equilibrium by means of a continuous iv infusion of [125I]T4 and [131I]T3 for a prolonged period. At the end of the infusion period, the animals were bled and perfused. Either whole small organs or weighed portions of tissues were homogenized in saline. The iodothyronines were extracted with ethanol-ammonia and separated by TLC. The [125I]T3/[131I]T3 ratios for the tissue homogenates and plasma were determined, and the relative contribution of the T3 derived from local T4 to T3 conversion [abbreviated: Lc T3 (T4)] to the total T3 in a given tissue was calculated. The endogenous T4 and T3 levels in the various organs were computed from the known specific activities of the labeled iodothyronines. The concentration of T4 in plasma greatly exceeded that found for tissue. Among the tissues examined, the T4 concentration was highest in the liver and lowest in cerebral cortex and cerebellum. T3 (per gram) was most abundant in the kidney and anterior pituitary gland and least abundant in the testis, epididymis, and erythrocytes. In contrast to the other tissues investigated, the concentration of T3 in several regions of the brain and anterior pituitary gland either equalled or exceeded that of T4. Plasma exhibited by far the lowest T3/T4 ratio. For most of the organs investigated the contribution of Lc T3(T4) appeared to be low. On the other hand, in 15 tissues, including the central nervous system, the local production of T3 accounted for one fifth or more of the total T3 content. Although there were no regional differences between the total T3 levels in the brain, the relative contribution of Lc T3(T4) was 65% in the cerebral cortex and only 22% in the spinal cord. The variation in the source of T3 in the various parts of the central nervous system may be related to regional differences in T4 and T3 metabolism. The fact that the present study demonstrates that the relationship between circulating T3 and intracellular T3 varies from one organ to the next may be important for accurate interpretation of plasma T4 and T3 levels and for designing optimal thyroid hormone replacement therapy for patients with hypothyroidism.

Animals↗
PubMed1984

Solubilized human thyrotrophin receptors behave as one class of high-affinity binding sites.

Evidence is presented justifying the conclusion that, in contrast to the dextran-coated charcoal technique, the widely used technique of separating bound and free TSH with polyethylene glycol is inadequate and yields inaccurate results. Optimum values for the concentration of Triton X-100, pH, salts, temperature and time of incubation were established for the TSH-TSH receptor interaction. According to Scatchard analysis, soluble TSH receptors behaved as one class of binding sites. The affinity constant for this class of binding sites (Ka 1.3 X 10(9) M-1) is identical to that for the high-affinity binding sites found in human thyroid membranes (Ka 1.2 X 10(9) M-1). No low-affinity binding sites could be detected after solubilization of membrane receptors. Chromatography experiments on Sepharose CL-6B indicated that, in excess TSH, each micelle containing TSH receptors (molecular weight 150 000) binds 4 [125I]TSH molecules. These data, together with the absence of low-affinity binding sites, led to the hypothesis that high-affinity TSH binding sites may be formed by the clustering of 4 low-affinity binding sites. Cross-reactivity experiments showed that both alpha- and beta-subunits are involved in the binding of TSH to its receptor; the TSH beta-subunit showed an increased cross-reactivity with soluble receptors.

Binding Sites↗
PubMed1984

Direct and quantitative measurement by immunoprecipitation assay of anti-thyrotrophin receptor antibodies in sera of patients with Graves' disease.

The presence of anti-TSH receptor antibodies in the sera of 32 patients with untreated Graves' disease, 21 patients with euthyroid autonomous multinodular goitre, nine patients with Hashimoto's disease and 22 normal controls, was investigated by means of a direct and quantitative immunoprecipitation assay (IPA). A comparison was made between the IPA anti-TSH receptor antibody titres, the thyrotrophin-binding inhibitor immunoglobulins (TBII) index determined by radio-receptor assay and the presence of circulating immune complexes (CIC); no correlation was found. Twenty-six (81%) of the 32 untreated patients with Graves' disease were IPA-positive; 16 (50%) had a positive TBII index. None of the patients with euthyroid autonomous multinodular goitre and none of the normal controls were IPA-positive and their TBII index was normal in all cases. Of the nine patients with Hashimoto's disease seven were IPA-positive and three had a positive TBII index. Of ten patients with Graves' disease still in remission none was IPA-positive and their TBII index was normal. Of 18 patients who relapsed after treatment, 13 were IPA-positive and only five had a positive TBII index. In seven patients with Graves' disease studied serially, anti-TSH receptor antibodies remained present in the sera of four, although the TBII indices normalized. For the five patients who relapsed, a rise in the anti-TSH receptor antibody titre at the time of the relapse was observed. It is concluded that not all anti-TSH receptor antibodies cause TSH-binding inhibition in the radio-receptor assay, and further evidence has been obtained that anti-TSH receptor antibodies are the cause of the hyperfunctioning of the thyroid gland in Graves' disease.

Adolescent↗
PubMed1984

The contribution of local thyroxine monodeiodination to intracellular 3,5, 3'-triiodothyronine in several tissues of hyperthyroid rats at isotopic equilibrium.

The local conversion of T4 as a source of intracellular T3 in several organs of both hypothyroid and euthyroid rats has recently been recognized to be an important phenomenon. In the present study the source and quantity of T3 in various peripheral tissues of hyperthyroid rats were investigated. Athyreotic rats received a continuous iv infusion of 3.5 micrograms T4/100 g BW X day over a prolonged period in order to attain hyperthyroid conditions. At the same time, the animals also received a continuous iv infusion of [125I]T4 and [131I]T3 until isotopic equilibrium was achieved. After the animals were bled and perfused, the source and quantity of T3 in various tissue homogenates and subcellular preparations of liver, kidney, and the anterior pituitary gland were analyzed. In spite of the elevated plasma T3 and T4 levels, the concentration of T3 in the cerebral cortex and cerebellum was within the normal range. The contribution of T3 derived from local T4 to T3 conversion [Lc T3(T4)] was rather low in both parts of the brain (cerebral cortex, 26%; cerebellum, 15%) when compared with values previously determined for euthyroid rats (cerebral cortex, 67%; cerebellum, 50%). It is concluded that in the cerebral cortex and cerebellum of hyperthyroid rats normal T3 concentrations were maintained by a compensatory decrease in the degree of Lc T3(T4). Whereas previous studies revealed that Lc T3(T4) contributes significantly to the T3 in the pituitary glands of both hypothyroid and euthyroid rats, this was not the case for the hyperthyroid animals; virtually all T3 was derived from plasma. The elevated plasma T3 levels caused an increased T3 content in both the homogenate and the nuclear fraction, leading to plasma TSH levels which were below the detection limit. It was found that the T3 in muscle was derived exclusively from plasma. Both the liver and kidney showed high concentrations of T3. Whereas Lc T3(T4) was the main source of T3 in the liver, it contributed only a minor fraction of the total T3 content in the kidney. In the liver Lc T3(T4) accounted for 50-53% of the T3 content in the mitochondrial and cytosolic fractions and about 64% in the microsomal fraction. In the kidney there was a small, but significant, amount of Lc T3(T4) in these subcellular fractions. In contrast, in the hepatic nuclei only 13% of the T3 was attributable to Lc T3(T4), whereas no Lc T3(T4) could be detected in the renal nuclei.

Animals↗
PubMed1984

The influence of partial food deprivation on the quantity and source of triiodothyronine in several tissues of athyreotic thyroxine-maintained rats.

In the present study the influence of partial food deprivation (PFD) on the quantity and source of T3 [i.e. T3 derived from local T4 to T3 conversion (Lc T3 (T4] vs. plasma-derived T3] in several rat tissues was investigated. Two groups of athyroid rats on a synthetic diet received a continuous iv infusion consisting of T4 (1.0 microgram/100 g BW X day), [125I]T4, and [131I]T3 over a prolonged period. For one group of rats the daily food intake was restricted by one third to maintain constant BW during the infusion period. At isotopic equilibrium the mean plasma T3, T4, and TSH levels for control-fed rats were: 38 ng/dl, 5.1 micrograms/dl, and 470 ng/ml, respectively. The values for rats on PFD were T3: 22 ng/dl, T4: 4.8 micrograms/dl, TSH: less than 70 ng/ml. The [125I]T3 and [131I]T3 contents of whole homogenates from liver, kidney, thigh muscle, cerebral cortex, cerebellum, and anterior pituitary gland as well as the subcellular fractions from liver, kidney (nuclei, mitochondria, microsomes, and cytosol), and anterior pituitary gland (nuclei) were determined (after extraction in ethanol) by thin layer chromatography. The contribution of Lc T3(T4) and the total T3 levels in these tissue preparations could then be calculated. In the cerebral cortex, cerebellum, and anterior pituitary gland of PFD rats plasma-derived T3 as well as Lc T3(T4) was decreased. The total T3 level in the liver did not change under PFD, owing to an increase in Lc T3(T4). It is possible that the release of hepatic Lc T3(T4) into the blood stream was reduced. In neither group was there appreciable Lc T3(T4) in muscle. In contrast to the other tissues investigated, the [131I]T3 tissue-plasma ratio for muscle had increased under PFD, suggesting a higher uptake of T3. As a consequence, the T3 levels in the muscles of PFD rats did not differ from those in normally fed animals. For both groups of rats the contribution of Lc T3(T4) in hepatic nuclei was far lower than that found for the other hepatic cellular fractions. This would suggest that the hepatic nucleus preferentially takes up plasma-derived T3. In both control-fed and PFD rats the bulk of renal T3 appeared to be exchangeable with plasma T3. Hence the T3 levels in renal nuclei were reduced under PFD. The nuclear T3 levels in the anterior pituitaries from PFD rats were markedly decreased. Therefore it is likely that other factors determine TSH secretion under PFD.

Animals↗
PubMed1984

Anti-TSH receptor antibodies in Graves' disease modulate the kinetic behaviour of autologous thyroid TSH receptors. Evidence of the IgG-induced cross-linkage of autologous TSH receptors.

The effect of the anti-TSH receptor antibodies present in the sera of 8 patients with Graves' disease on the affinity constant (Ka) and the number (R) of TSH receptors in autologous human thyroid plasma membranes was investigated. Kinetic analysis of [125I]bTSH binding to human thyroid plasma membranes in the presence of autologous Graves' and normal gammaglobulins was carried out by means of a computer fitting programme. Analysis of the TSH-TSH receptor interaction in the presence of TSH alone yielded curvilinear Scatchard plots, indicating the existence of two independent classes of binding sites (high affinity Ka: 8.5 +/- 4.8 X 10(8) M-1; low affinity Ka: 5.3 +/- 2.7 X 10(6) M-1). Similarly the Scatchard plot for this interaction in the presence of normal gammaglobulins is also curvilinear. Linear Scatchard plots, indicating the existence of only one class of high affinity TSH binding sites (Ka: 3.5 +/- 1.8 X 10(8) M-1), were obtained for both autologous gamma-globulins and pure IgG from 8 patients with Graves' disease. The number of high affinity TSH binding sites in the presence of Graves' gammaglobulins had increased on the average by a factor 3.76 +/- 0.74 (SD) with respect to the number found in the presence of normal gammaglobulins. This marked change in the kinetic behaviour of the TSH binding sites provided evidence that there is a direct interaction between anti-TSH receptor antibodies and autologous TSH receptors. Divalency of Graves' IgG or linkage of Fab fragments by anti-Fab antiserum proved to be necessary to produce this specific change in the kinetic behaviour of TSH binding sites. Graves' IgG monovalent Fab and Fc fragments had no effect. We suggest that the mechanism by which anti-TSH receptor antibodies in Graves' disease mimick the biological action of TSH is the IgG-induced cross-linkage of TSH receptors.

Adult↗
PubMed1983

Sources and quantity of 3,5,3'-triiodothyronine in several tissues of the rat.

The local conversion of thyroxine (T4), which is an important source of intracellular 3,5,3'-triiodothyronine (T3) in several rat tissues, has been subject of recent investigations. In the present study the regulation of this phenomenon in vivo was investigated in various peripheral tissues of the rat. Intact euthyroid and radiothyroidectomized (Tx) rats received a continuous intravenous infusion of [125I]T4 and [131I]T3 until isotope equilibrium was attained. In addition to the labeled iodothyronines, Tx rats received a continuous intravenous infusion of 0.2 or 1.0 microgram carrier T4/100 g body wt per d, to create hypothyroid or slightly hypothyroid conditions, respectively. After the animals were bled and perfused the contribution of T3 derived from local conversion of T4 to T3 [Lc T3(T4)] to the total T3 in homogenates from several tissues and subcellular fractions from the liver, kidney, and anterior pituitary gland could be calculated. In all experiments T3 in muscle was derived exclusively from the plasma. In the cerebral cortex and cerebellum, however, most of the intracellular T3 was derived from the intracellular conversion of T4 to T3. It is demonstrated that for hypothyroid rats an increased relative contribution of Lc T3(T4) reduced the loss of total T3 in the brain. This phenomenon was also encountered for the anterior pituitary gland, although in this tissue the proportion of the total tissue T3, contributed by locally produced T3 was considerably lower than the values found for the cerebral cortex and cerebellum in all experiments. The present findings, regarding the source and quantity of pituitary nuclear T3 strongly suggest that both plasma T3 and T4 (through its local conversion into T3) play a role in the regulation of thyrotropin secretion. The contribution of Lc T3(T4) to the total pituitary nuclear T3 was of minor importance in euthyroid rats (approximately 20%), compared with that found for both groups in T4-supplemented athyreotic rats (approximately 40%). The total T3 concentration in the liver decreased from euthyroid to hypothyroid rats and was associated with a decrease in the tissue/plasma T3 concentration gradient. A minor proportion of hepatic T3 was contributed by Lc T3(T4), which in fact decreased significantly from the euthyroid to the hypothyroid state. In contrast to other subcellular fractions from the liver, no Lc T3(T4) could be demonstrated in the nuclear fraction. It is suggested that the liver plays an important role with respect to regulation of the circulating T3 concentration. In the kidney, a very small proportion of the total T3 was derived from locally produced T3 in all experiments (4-7%). As found in the liver, all nuclear T3 appeared to be derived from the plasma. In contrast to the liver, subcellular T3 pools in the kidney seemed to be exchangeable.

Animals↗
PubMed1983

Anti-thyrotrophin receptor antibodies in Graves' disease as demonstrated directly by immunoprecipitation assay.

An immunoprecipitation assay was developed to determine the presence of antibodies against human TSH receptors. With this assay we were able to demonstrate that in comparison with sera from normal controls. 24 out of 30 (80%) sera from patients with untreated Graves' disease could immunoprecipitate more [125I]TSH-TSH receptor complexes. In 9 assays, an average of 14.1 +/- 3.7% (SD) of the [125I]TSH-TSH receptor complexes was immunoprecipitated by the 30 Graves' sera vs 9.8 +/- 3.0% by the normal pool serum (n = 23) (P less than 0.001) and 7.7 +/- 2.8% by the 22 normal sera (P less than 0.001). One serum of the 24 positive Graves' sera was studied in detail. The results suggest that this serum contained an anti-TSH receptor auto-antibody directed towards a different determinant on the TSH receptor than the TSH binding site.

Adult↗
PubMed1983

The effect of propylthiouracil and methimazole on the peripheral conversion of thyroxine to 3,5,3'-triiodothyronine in athyreotic thyroxine-maintained rats.

The effect of prolonged oral administration of PTU and MMI on the local conversion of T4 to T3 was studied in T4-maintained athyreotic rats. For this purpose the rats were equilibrated with [125I]T4 and [131I]T3 by means of continuous iv infusions. PTU treatment reduced the MCR of both T4 and T3, as well as the T3 levels in plasma, muscle, liver, kidney and cerebellum. In the cerebral cortex the total intracellular T3 concentration was not affected, while in the pituitary it even increased. The amount of T3 derived from local conversion of T4 to T3 (LcT3(T4)) was reduced in the liver. PTU treatment did not influence Lc T3(T4) in the cerebellum, but did cause an increase in the amount of T3 derived from this source in the cerebral cortex and the pituitary gland (both the homogenate and the nuclear fraction). The results indicate that in contrast to that in liver, local T3 production in the brain and pituitary must occur predominantly via a pathway which is not inhibited by PTU. In MMI-treated rats the total T3 concentration in the cerebral cortex and cerebellum was not altered, whereas both the MCR of T3 and the T3 levels in plasma and various other tissues were elevated. The relative contribution of Lc T3(T4) increased in liver and was reduced in the cerebral cortex, cerebellum and pituitary gland. In all experiments in liver the contribution of Lc T3(T4) to nuclear T3 was negligible, whereas this was not the case for the other hepatic subcellular fractions. As in liver, virtually all renal nuclear T3 was derived from plasma. The present findings suggest that the production of T3 in liver and kidney, and its subsequent release into the blood, may provide a mechanism for the regulation of plasma T3 levels but is not a direct source of their nuclear T3. In the pituitary gland and the brain local T4 to T3 conversion functions as a source of T3 for the control of local utilization. In this respect the maintainance of constant T3 levels in the brain might be important. These differences among tissues suggest that different mechanisms are involved in T4 5'-deiodination.

Animals↗
PubMed1982

The influence of intravenous infusion of electrolytes on the diurnal excretory rhythms.

In freely moving rats the diurnal in electrolyte excretion was studied. Food was available during either the dark or the light period. The lights were on from 0800-2000; the dark phase extended from 2000-0800 hrs. The electrolyte excretory rhythms were studied during a control period, in which the minerals were present in the food, and during experimental periods, when successive minerals were not present in the food but were instead given by constant intravenous infusion. For both groups the excretory rhythms of K, Mg and P persisted during continuous infusion but the times of maximum and minimum excretion differed. Day-fed animals exhibited a remarkable decrease in amplitude during the mineral infusion period. In contrast, the calcium excretory pattern was only influenced by the feeding period.

Animals↗
PubMed1982

Propranolol improves the impaired TSH response to TRH in patients with autonomously functioning euthyroid multinodular goitre.

Ten patients with autonomously functioning euthyroid multinodular goitre received propranolol (Inderal Retard 160 mg daily) for 4 weeks in order to investigate whether normalization of the TRH test or an increased TSH response to TRH could be obtained by decreasing serum T3 levels. Serum T3 decreased significantly after 2 and 4 weeks of propranolol administration. Serum T4 increased during this period, although the change was only significant after 4 weeks of propranolol. T3 resin uptake did not change. The TSH response to TRH increased significantly during the administration of propranolol. Mean delta TSH basally was 1.0, range 0-3.9 mU/l, and mean delta TSH after 4 weeks of propranolol was 2.4, range 0-9.3 mU/l. A strong correlation was found between the increase in delta TSH and the decrease in serum T3 after 4 weeks of propranolol. After withdrawal, delta TSH and T3 returned to premedication levels. Our data suggest that T3 is an important factor in the impairment of the TSH response to TRH in our patients. Normalization of the TRH test was, however, not obtained. These findings support the concept of subclinical hyperthyroidism in 'euthyroid' multinodular goitre with autonomous function.

Adult↗
PubMed1982

Properties of thyrotrophin receptors in human thyroid membranes.

The influence of pH, salts, temperature and time of incubation on the binding of [125I]thyrotrophin to its human thyroid receptor was studied. Optimal binding was achieved at pH 7.0--7.6. Pre-incubation of membrane receptors at pH 6.0 resulted in a 60% loss of binding. There was dynamic equilibrium, as demonstrated by kinetic experiments. Scatchard analysis yielded non-linear plots with apparent affinity constants of 1.9 x 10(9) M-1 and 3.7 x 10(7) M-1. The concentration of [125I]thyrotrophin used in the experiments (1.2--2.2 pM) approximated normal human serum thyrotrophin concentration.

Cell Membrane↗