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M Zakarija

Publications and source records attributed to M Zakarija.

At least 55 records · Page 3Linked to original sources
PubMed1980

The thyroid-stimulating antibody of Graves' disease: evidence for restricted heterogeneity.

The thyroid-stimulating antibody (TSAb) of Graves' disease was shown to have a relatively constant pH on preparative isoelectric focusing; the fraction of pH 8.5-9.0 was maximal in thyroid-stimulating potency but inhibition of thyrotropin-binding (another property of Graves' disease IgG) was most marked with pH 9.5-10.6 fraction. H and L chains of TSAb-IgG were separated and H original (HO) was combined with L original (LO) and with Bence Jones L kappa and L lambda. Only HO + LO restored (minimal) bioactivity. Of isolated TSAb-IgG kappa and TSAb-IgG lambda only IgG lambda was thyroid stimulating. Sub-classes (IgG3 and IgG 1 + 2 + 4) of TSAb-IgG were prepared and with all of 6 sera TSAb was in IgG 1 + 2 + 4 with none in IgG3. These data combine to suggest heterogeneity of this autoimmune antibody.

Antibody Specificity↗
PubMed1980

Thyrotropin binding to rat thyroid membranes: reduced capacity associated with goitrogenesis.

To investigate a possible role of TSH in the regulation of its own receptor, a sensitive assay of [125I]TSH tropin binding to rat thyroid membranes was used. With 1 mM MgCl2 in the buffer, Scatchard analysis of displacement of TSH gave a curvilinear plot with a high affinity, low capacity (K1, 3.4 nM; Q1, 3.1 pmol/microgram) and a low affinity, high capacity binding site (K2, 0.54 microM; Q2, 1.2 X 0.1 nmol/microgram). Feeding rats propylthiouracil led to a decrease in [125I]TSH binding (expressed either per U protein or per wet wt of tissue) that was related to the duration of treatment. Evaluation by Scatchard analysis showed that this was due to a loss of binding sites, e.g. a 50-60% decrease after 1 month of propylthiouracil treatment; affinity was actually slightly increased in the goitrous tissue. This change in the number of TSH-binding sites was readily reversed in association with the suppression of TSH in vivo either by injections of T3 for 3 days or more by feeding a normal diet for 1 month. Thus, the data are compatible with TSH, that is in high concentration in the serum of rats fed propylthiouracil, exerting a downregulatory influence on its own receptors.

Adenylyl Cyclases↗
PubMed1980

Influence of cholera toxin on in vitro refractoriness to thyrotropin of thyroids from rats fed propylthiouracil.

Using an increase in the concentration of cAMP as an index of stimulation, we previously reported that in vitro thyroid tissue of rats fed a goitrogenic diet (0.1% propylthiouracil in Purina) were unresponsive to TSH. We now show that the addition of cholera toxin (0.1-1.0 microM) to fragments of normal thyroid enhanced the concentration of cAMP. Subsequent exposure of the tissue to TSH resulted in a further increase in the concentration of cAMP, and there was statistical evidence of interaction or potentiation between the effects of TSH (20 mU/ml) and cholera toxin (1.0 microM). With fragments of thyroid from animals fed propylthiouracil (i.e. unresponsive in vitro to TSH), an increase in the concentration of cAMP was effected by 1 or 9 microM cholera toxin, and prior exposure to 9 microM toxin caused the tissue to be responsive to TSH. Unresponsiveness of the goitrous tissue was associated with a reduced capacity of the membrane to bind [125I]iodo-TSH although the affinity of the binding sites was unaffected. Cholera toxin at 0.1 microM enhanced and at 1 microM diminished the binding of [125I]iodo-TSH to membranes from either normal or goitrous glands, and these effects also reflected influences on the capacity rather than on the affinity of the binding sites. It is postulated that the unresponsiveness to TSH of thyroid tissue from rats fed propylthiouracil represents a down-regulation of receptor capacity, and this is effected by the binding sites becoming relatively inaccessible, rather than nonexistent.

Adenylyl Cyclases↗
PubMed1980

Influences of cholera toxin on thyroid stimulation by thyrotropin and thyroid-stimulating antibody.

Thyroid-stimulating antibody (TSAb) is an immunoglobulin G (IgG) occurring in the blood in hyperthyroid Graves' disease patients; it stimulates the thyroid in a manner analogous to the action of TSH, i.e. by activation of adenylate cyclase. Since cholera toxin is also known to stimulate thyroid adenylate cyclase, we studied possible interaction of the enterotoxin on effects of TSAb and TSH using slices of canine thyroid in vitro and an increase in the concentration of cAMP as endpoint. Normal human IgG, known to inhibit the binding of [125I]-iodo-TSH to thyroid membranes, decreased stimulation of thyroid slices by TSH; this inhibitory effect occurred also with preparations of TSAb (inevitably comprised mainly of normal IgG) that were themselves stimulatory. The cholera toxin effect was not prevented by normal IgG and, by factorial analysis of variance, was shown to potentiate the action of subsequently added TSAb or TSH. There was also positive interaction of the effect of TSAb with the combination of TSH and cholera toxin. The data indicate that responses of thyroid tissue to TSAb and TSH are readily influenced by effects of other membrane-active agents (in the present context, normal IgG and cholera toxin).

Animals↗
PubMed1980

Clinical significance of assay of thyroid-stimulating antibody in Graves' disease.

We correlated thyroid-stimulating antibody (direct thyroid stimulation method) with the clinical course of 187 patients with Graves' disease. Of 64 patients with newly diagnosed hyperthyroidism, 59 were positive; 36 of 38 patients tested early in therapy were positive. Twenty-eight patients received antithyroid drug therapy, and thyroid-stimulating antibody was measured at cessation of therapy; 13 patients, negative in the assay, remained in remission, and of 15 relapsed cases 12 were positive. Of 57 patients previously treated by various means for hyperthyroidism, 34 were positive, and they primarily had had relapse after initial treatment, then ablative therapy causing hypothyroidism. Six of 10 patients with euthyroid ophthalmopathy had a positive assay and an abnormal thyrotropin-releasing hormone (TRH) test or thyroid suppression test; the four negative patients had a normal TRH test. Thus measurement of thyroid-stimulating antibody appears effectively to reflect activity of the underlying disturbance in Graves' disease.

Antibodies↗
PubMed1978

The influence of normal human IgG and of thyroid-stimulating antibody (TSAb) on the binding of thyrotropin to thyroid plasma membranes.

The influence of serum IgG from normal and Graves' disease subjects on the binding of 125I-thyrotropin to isolated thyroid membranes was studied. IgG from either source inhibited binding in a concentration -dependent fashion. Human membranes were more sensitive to the human IgG than were bovine thyroid membranes and, when membranes were purified by discontinuous sucrose gradient centrifugation, they were more sensitive than were those less-purified, obtained by differential centrifugation. Using a Dixon plot, inhibition by normal IgG showed non-competitive kinetics. Fab fragments were more effective, on an equimolar basis, than was intact normal IgG, but were less potent when Graves' disease IgG was the parent molecule; this difference implies distinct modes of inhibition of thyrotropin-binding. The degree of inhibition by normal IgG was variable so that multiple control preparations are required to assess the additional effect characteristic of IgG from the subject with Graves' disease.

Animals↗
PubMed1978

Zoological specificity of human thyroid-stimulating antibody.

The zoological specificity of human thyroid-stimulating antibody (TSAb) that occurs in the blood in Graves' disease was examined by assessing its effect on the thyroid of the dog, guinea pig, calf, and mouse as well as that of man. With all but murine glands, thyroid stimulation was assayed by measuring the increase in the concentration of cAMP in the thyroid slices or fragments after 2 h of incubation in buffer containing TSAb. Effects on the thyroid of the mouse were monitored by the in vivo bioassay for LATS. Sera from 33 patients with Graves' disease were obtained and concentrates of TSAb were prepared by precipitation of IgG with 1.64 M (NH4)2SO4. These all stimulated the human thyroid, 13 were LATS-positive, and they variably affected the tissues of other species; of 27 tested, 14 stimulated the thyroid of the dog, 8 out of 23 stimulated the thyroid of the guinea pig, and 12 out of 16 stimulated the gland of the calf. The more potent the TSAb as assayed with human tissue, the more likely was it to stimulate other species of thyroid; however, frequent exceptions occurred. In a separate analysis of 35 LATS-positive preparations of TSAb, correlation between the responses in the LATS and human thyroid slice assays was statistically significant (P less than 0.001). The data are compatible with the view that stimulation by TSAb of nonhuman thyroids, including the murine as in the LATS bioassay, reflects cross-reaction of this immunoglobulin with an antigen that has sufficient similarity to the human molecule to be recognized by the human antibody.

Animals↗
PubMed1978

Adsorption of thyroid-stimulating antibody (TSAb) of Graves' disease by homologous and heterologous thyroid tissue.

Immunoglobulin G purified from the serum of patients with Graves' disease, stimulated the thyroid of man, calf, and guinea pig (cAMP accumulation as the end-point) in vitro, and the thyroid of the mouse in vivo (LATS bioassay). The stimulatory effect on the thyroids of all four species was removed by adsorption of the immunoglobulin G to human thyroid membranes and was diminished to a proportionately similar degree by adsorption with bovine thyroid membranes. All activity, as assessed by stimulation of the human thyroid in vitro. was recovered from both human and bovine membranes by elution with 2 M NaSCN solution. The data support the concept that the thyroid-stimulating antibody of Graves' disease is homologous to a human thyroid antigen and, in some instances, cross-reacts with a similar antigen in the thyroid of a distant species and so stimulates the heterologous gland.

Adsorption↗
PubMed1977

Effects of thyrotropin and thyroid hormones in vivo on thyroid responsiveness to thyrotropin in vitro.

The thyroid gland of rats fed propylthiouracil is known to be unresponsive in vitro to thyrotropin; to investigate further the underlying mechanism groups of rats were variously treated with propylthiouracil and thyroid hormone or subjected to hypophysectomy. In vitro responsiveness of the thyroids was tested by measuring an increase in the concentration of c AMP when thyrotropin or prostaglandin E1 was added to the medium. Results showed that responsiveness to thyrotropin partially returned with rats fed prophylthiouracil and hypophysectomized 5, but not 2, days before death; hypophysectomy of normal rats led to increased in vitro responsiveness to thyrotropin and this was partially reversed by injections of thyrotropin for a week before death. Administration of thyroid hormone had little effect in these investigations and in vitro responsiveness to prostaglanding E1 was not consistently influenced by any of the in vivo regimens. From this experience we conclude that, at least as studied in vitro, circulating thyrotropin has a significant role in modulating responsiveness of the thyroid to thyrotropin.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1977

Characteristics of thyrotropin binding to bovine thyroid plasma membranes and the influence of human IgG.

The characteristics of binding of 125I-labeled bovine thyrotropin to bovine thyroid plasma membranes were studied. At pH 7.5, 0 C, specific binding was maximal in 3 hr and was progressively inhibited by Na+, Mg++, Ca++ and (NH4)2 SO4 in concentrations of 25 mM and greater. Affinity constants of l.047 X 10(8)M-1 and 0.57 X 10(6)M-1 were obtained for two binding sites and Hill plots provided a mean slope of 0.86, suggesting negative cooperativity. Addition of 1-thyroxine or 1-triiodothyronine at 0.5 ng to 50 microgram per ml had no significant effect but propylthiouracil (10(-7) to 10(-5)M) and KC104 (10(-7) to 10(-4)M) had biphasic effects, first enhancing and then inhibiting binding. Normal human serum IgG, particularly two fractions (3 and 4) obtained by chromatography on columns of cellulose phosphate, and an alpha-globulin - rich fraction from chromatography of serum proteins on diethylaminoethyl cellulose, inhibited binding at concentrations of 0.5 mg per ml or greater. Thus two possibilities are that normal human serum globulins either compete with thyrotropin for its receptor on thyroid plasma membranes or, in binding to the membranes, cause such perturbation as to affect adversely the conformation of the receptor for thyrotropin.

Animals↗
PubMed1976

A reconsideration of a thyroid-stimulating immunoglobulin as the cause of hyperthyroidism in Graves' disease.

Several assays for thyroid-stimulating immunoglobulins in the blood in patients with Graves' disease have been described recently; depending upon the method, different names have been used and distinct entities thus implied. Using an increase in cyclic AMP in the human thyroid slice after 2 h of incubation as an index of thyroid stimulation, we identified thyroid-stimulating activity in all of an unselected series of sera from 11 patients with hyperthyroidism of Graves' disease, but long-acting thyroid stimulator, by mouse bioassay, in only three. The theory is proposed that the thyroid-stimulating immunoglobulin is probably present in all such patients; it may be seen as a polyclonal antibody to a single human antigen that has a variable cross-reaction with a corresponding thyroid antigen in the mouse and in other species.

Animals↗