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L J DeGroot

Publications and source records attributed to L J DeGroot.

At least 217 records · Page 12Linked to original sources
PubMed1977

Liver protein kinase activity and triiodothyronine.

Protein kinase activities were determined in liver from normal, thyroidectomized and triiodothyronine (T3)-treated rats. Changes related to thyroid hormone were observed in cytosol and nuclear protein kinase activities. When protamine was used as substrate for phosphorylation, thyroidectomy induced a decrease of protein kinase activity associated with nuclei but an increase of activity was found in the cytosol. Fifteen hours after injection of T3 the levels in nuclei and cytosol were restored to normal. When casein was used as substrate, hypothyroidism led to a lowering of protein kinase activity in both fractions and T3 treatment augmented the activity in both. These studies suggest that thyroid hormones modify hepatic protein kinase activity. Results differ depending upon the substrate used. The hormones also appear to alter the subcellular distribution of some protein kinase activities.

Animals↗
PubMed1977

Triiodothyronine receptors during maturation.

Capacity of rat liver nuclear triiodothyronine (T3) binding protein (NTBP) for T3 more than quadruples from birth through 50-120 days, whether related to DNA or weight of tissue. Ka for T3 doubles during this interval. T3 content of nuclei nearly parallels capacity. The proportion of receptors occupied by T3 is 0.3 at birth, falling to .16 in old rats. In contrast to these changes in liver content of T3-receptor complex, mitochondrial alpha-glycerophosphate dehydrogenase activity changes relatively less during maturation. Administration of estrogen, testosterone, and dexamethasone to immature female rats did not alter NTBP capacity of affinity.

Aging↗
PubMed1977

Serum albumin and antibodies in the diagnosis of thyroid cancer.

Anti-thyroglobulin antibodies, anti-thyroid microsomal antibodies, serum thyroglobulin, and carcinoembryonic antigen were assayed in sera of patients with a history of thyroid irradiation and in patients with thyroid cancer. In irradiated patients, the frequency of positive results for each test was increased above the frequency found in a control population, with a significant increase at P less than .05 for TGHA and TG levels. However, the tests (with the exception of serum thyroglobulin) did not clearly segregate irradiated patients with benign or malignant lesions from those with no clinically detectable abnormalities. Elevations of serum thyroglobulin above 300 ng/ml were found only in patients with thyroid cancer, but in these patients the diagnosis was usually clinically obvious.

Adult↗
PubMed1977

Compensated low-dose 131I therapy of Graves' disease.

To minimize the high rate of residual thyrotoxicosis encountered in low-dose 131I therapy of Graves' disease, we have treated 62 patients with a low-dose 131I protocol that includes a compensation for thyroid size. Dose varied between 40 muCi retained/g for glands of normal size to 100 muCi/g for glands of 100 g or greater. Mean dose was 51.9 muCi/g. At 1 year after therapy, 66.1% of subjects were euthyroid, 9.7% hypothyroid, and 24.2% hyperthyroid, a significant improvement (P less than 0.01) over our previous experience using 50 muCi/g independent of gland size. Several factors, other than 131I dose, which might influence the outcome of therapy, were investigated. Initial free thyroxine index observed before therapy was found to have prognostic significance. Hypothyroidism developed only in patients having an initial free thyroxine index of 22.5 or less (about 2.5 times the upper limit of normal in our laboratory).

Adult↗
PubMed1976

Binding of nuclear triiodothyronine (T3) binding protein-T3 complex to chromatin.

Nuclear tirrodothyronine (T3) binding protein (NTBP)-T3 complex, prepared from liver nuclei of rats given [125I]T3 in vovo, rebinds to rat nuclear chromatin at pH 7.4 and at low, but not high, KCl concentrations. Liver NTBP-T3 complex binds to chromatin from liver, kidney, heart, brain, testis, and spleen. Binding was depressed at pH8, by addition of 10 mm CaCl2 or 100 mM MgCl2, and by 1 mM GTP or UTP. Although heart chromatin bound the most NTBP-T3 complex and brain the least, there is no clear separation of binding activity on comparison of three T3-responsive tissues (heart, liver, kidney) to the T3 insensitive tissues. Under the conditions of these experiments, there was no evident competition for binding sites on any of the six chromatins tested.

Animals↗
PubMed1976

Thyroid cancer: relationship to radiation exposure and to pregnancy.

Exposure to radiation results in an increased occurrence of nodularity to the thyroid and, more important, the development of cancer in a significant proportion of patients. Near-total thyroidectomy is recommended in those patients with a history of irradiation who are found on physical examination of the thyroid to have one or more nodules. Although pregnancy appears to have no effect on the course of thyroid carcinoma and the tumor has no effect on pregnancy, because of the numerous stimuli to thyroid growth during pregnancy, we feel that pregnancy is best avoided by women with known residual disease.

Adolescent↗
PubMed1975

Thyroid carcinoma.

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Adenocarcinoma↗
PubMed1975

Triiodothyronine binding to isolated liver cell nuclei.

Nuclei of euthyroid rat liver have been prepared from homogenates by sedimentation through 2.3M sucrose with or without a 0.25% Triton wash. Triiodothyronine is accumulated by these nuclei during incubation in vitro in solutions containing 0.32M sucrose, 1mM MgCl2 and 0.02M Tris-Cl buffer at pH 7.4 or 7.85. Specific T3 binding sites occupied at 10-1,000 pM T3 are saturated by excess unlabeled T3 (0.15 muM). Specific T3 binding at 20 C is maximal at 203 hr nad is proportional to amount of nuclei. Calcium ion enhances nuclear integrity by reduces T3 accumulation. EDTA and phosphate ion cause nuclear damage but increase T3 accumulation. Binding is unaffected by inhibition of energy dependent reactions or of RNA synthesis. It is markedly increased under certain conditions by addition of dithiothreitol (DDT). Binding does not require mediation of a cytosol protein. T3 binding is not prevented by RNAse or DNAse, but is obliterated by pronase. Te binds to a nuclear iodothyronine binding protein (NTBP) to form an NTBP-T3 complex similar to that form-d after in vivo administration of the hormone. The complex can be extracted from the nuclei by 0.4M KC-. T3 present in the NTBP-T3 complex resists accumulation by anion exchange resin at 0-2C, but is bound by resin after 20 min at 37C or after addition of 0.1 mM p-hydroxymercuribenzoate. At pH 7.85 and with 5 mM DTT, the apparent Ka for isolated nuclei is 0.2 times 10-10M-1 and the capacity is 508 pg T3/g wet tissue or 53 times 10-15 moles T3/100 mug DNA. The data may not represent total capacity, but rather the amount of T3 dissociated during the period of incubation so that NTBP-T3 can be exchanged with labeled T3. Among analogues tested, triiodothyroacetic acid appears to bind with four times the affinity of L-TX, D-T3 binds with equal affinity, and L-T4 with one-fourth the affinity of T3.

Animals↗
PubMed1975

Participation of NADPH-cytochrome C reductase in thyroid hormone biosynthesis.

Purified rat liver NADPH-cytochrome c reductase supports iodination of tyrosine in a system including NADPH, cytochrome c and thyroid perioxidase. Catalase inhibits the iodination of tyrosine, while superoxide dismutase has no effect. Antibody developed in the rabbit against purified rat liver NADPH-cytochrome c reductase inhibits both reduction of cytochrome c and tyrosine iodination supported by the enzyme. The antibody forms a single precipitation line with thyroid extract, and inhibits NADPH cytochrome c reductase activity of the thyroid. The antibody partially inhibits iodination in a thyroid mitochondrial-microsomal fraction, but does not inhibit NADH-dependent iodination. The immunochemical studies indicate the participation of NADPH-cytochrome c reductase in thyroidal H2O generation, and the independent existence of NADPH-dependent and NADH-dependent H2O2 generation mechanisms in the thyroid.

Animals↗
PubMed1975

Triiodothyronine binding to liver nuclear solubilized proteins in vitro.

Nuclear proteins extracted from purified nuclei with 0.4M KCl at pH 7.4 OR 8.5 are able to bind L-triiodothyronine (T3) giving rise to nuclear thyroid hormone binding protein-T3 (NTBP-T3) complexes. Binding is maximum in 3 h at 20 C. It is thermolabile even at 36 C, inhibited by p-hydroxymercuribenzoate and markedly enhanced by dithiothreitol. Optimum pH is between 7.8 and 8.5. Divalent cations are not necessary. The NTBP-T3 complex exhibits similar anodal electrophoretic migration in polyacrylamide gel at pH 8.5, whether formed in vivo or in vitro. Scatchard plots obtained with various amounts of T3 from 0.15 nM TO 0.15 MUM and either unlabeled nuclear proteins or in vivo formed NTBP-[125I]-T3 complexes, give apparent association constants K-a of 0.2 X 10-10 M minus at pH 7.4 and 0.8 X 10-10 M minus 1 at pH 8.5. Capacity is about 0.5 pmol T3 per mg protein or 800 pg/g liver. The presence of dithiothreitol markedly enhances the Ka. The nuclear binding sites are not highly specific for L-T3 since they are able to bind D-T3 with almost equal affinity and triiodothyroacetic acid with a higher affinity. L-thyroxine (T4) can also displace L-T3 but with about 10-fold lesser effectiveness. Nuclear binding proteins of low capacity and high affinity have been demonstrated in vitro. The NTBP-T3 complexes formed in vivo, with whole nuclei, or in vitro are indistinguishable.

Animals↗