PubMed Health⌕ Search

Biomedical subjects

G N Burrow

Publications and source records attributed to G N Burrow.

At least 19 recordsLinked to original sources
PubMed1992

Inhibition of thyrotropin-induced DNA synthesis in thyroid follicular cells by microinjection of an antibody to the stimulatory G protein of adenylate cyclase, Gs.

Thyrotropin (TSH) is an important regulator of thyroid follicular cells. While its role in the maintenance of differentiated functions is undisputed, its role as a mitogen is less clear. TSH induces DNA synthesis and cell proliferation in some cells, while in others, TSH is mitogenic only in the presence of additional growth factors such as insulin-like growth factor-1. TSH causes elevations in intracellular cAMP and is thought to utilize this second messenger system in its mitogenic action. We studied TSH as a mitogen in Wistar rat thyroid cells (WRT) (Brandi, M. L., Rotella, C. M., Mavilia, C., Franceschelli, F., Tanini, A., and Toccafondi, R. (1987) Mol. Cell. Endocrinol. 54, 91-103) and examined the role of the guanine nucleotide binding protein, Gs, in its mitogenic action. WRT cells synthesized DNA in response to TSH and elevations in cAMP. In addition, TSH caused a rapid stimulation of an indicator gene whose expression is regulated by cAMP response elements. Following microinjection of an inhibitory polyclonal antibody raised against the Gs protein, both TSH-induced changes in gene expression and DNA synthesis were significantly reduced. These results demonstrate that virtually all of the mitogenic action of TSH is transduced through the Gs protein in WRT cells, presumably through the regulation of adenylate cyclase. Whether all or only part of TSH action is mediated by cAMP and the cAMP-dependent protein kinase remains to be determined.

1-Methyl-3-isobutylxanthine↗
PubMed1992

Iodide induces transforming growth factor beta 1 (TGF-beta 1) mRNA in sheep thyroid cells.

We examined TGF-beta mRNA levels in primary sheep thyroid cell cultures to determine whether the inhibitory effects of iodide on thyroid cells could be explained by an induction of TGF-beta mRNA and if this induction was mediated by iodine organification. Thyroid cells were incubated with TSH and five additives (insulin, somatostatin, growth hormone, transferrin, and glycyl-L-histidyl-L-lysin) for 2-3 weeks and then were exposed to sodium iodide (NaI) or 1-methylimidazole-2-thiol (methimazole, MMI), or both for 72 h. Iodide at 10(-6) M and 10(-4) M significantly increased the amount of TGF-beta mRNA as determined by Northern blot analysis with a rat TGF-beta 1 cDNA probe. This increase in TGF-beta 1 mRNA was abolished by the addition of methimazole, an inhibitor of organification. These data indicate that the effects of iodide on thyroid growth and function may be mediated by a process that involves organification of iodide and increases in TGF-beta 1 mRNA levels.

Analysis of Variance↗
PubMed1992

Control of thyroid secretion: effects of stimulators of protein kinase C, thyrotropin, and calcium mobilization on secretion of iodinated compounds from sheep thyroid cells.

We have compared and contrasted the abilities of TSH and agents capable of discretely activating the cAMP-dependent protein kinase, protein kinase C, or calcium mobilization to influence the secretion of iodinated compounds from cells prelabeled with iodide and blocked from further organification with methimazole. We found that calcium mobilization induced by A23187, protein kinase C activation induced by 12-O-tetradecanoyl phorbol 13-acetate (TPA) and TSH all stimulated the secretion of iodinated compounds. The effects of TSH were mimicked by forskolin and those of TPA by a synthetic diacylglycerol, sn-1,2-dioctanoylglycerol. The effects of TPA were partially inhibited by staurosporine whereas those of TSH were not. Epidermal growth factor and norepinephrine were without effect on thyroid secretion. The effects of A23187 and TPA were synergistic. The effects of TSH and TPA were not and the increased secretion induced by either agent was partially prevented by the combination. Preincubation of cells with TSH desensitized the cells to further stimulation by TSH but the stimulatory effects of TPA were unaffected. Exposure of cells to medium without calcium also induced loss of iodinated compounds which was partially prevented by TSH or forskolin but not TPA. TSH did not stimulate the rapid production of inositol trisphosphate production. We conclude that the mechanisms by which TSH (through stimulation of cAMP) and stimulators of other intracellular pathways exert their effects on secretion of iodocompounds, differ. Activation of protein kinase C and acute production of inositol trisphosphate do not appear to be involved in the mechanism of action of TSH in stimulating thyroid secretion but calcium mobilization is implicated.

Alkaloids↗
PubMed1991

Thyroid disease and pregnancy.

Thyroid disease is common in younger women and may be a factor in reproductive dysfunction. This probably only applies to severe cases of hyper- or hypothyroidism. Once adequately treated, neither of these disorders significantly impacts on fertility. The key is to recognize and to treat thyroid disorders in the reproductive-age woman before conception. Thyroxine therapy and even antithyroid drug therapy should be continued during pregnancy as necessary. Pregnancy is a euthyroid state that is normally maintained by complex changes in thyroid physiology. The fetal and neonatal hypothalamic-pituitary-thyroid system develops independently, but it may be influenced by thyroid disease in the mother. Early pregnancy is characterized by an increase in maternal T4 secretion stimulated by hCG and an increase in TBG, resulting in the elevated total serum T4 in pregnancy. The debate continues as to whether maternal T4 is important in early or late fetal brain development. If so, the physiologic changes in thyroid hormone secretion and transport in early pregnancy would help to ensure that a sufficient amount of thyroid hormone was available. There is new evidence in human subjects that substantial maternal T4 can cross the placenta during pregnancy, and this may be particularly important when fetal thyroid function is compromised as a result of congenital hypothyroidism. Maternal and fetal/neonatal outcomes in pregnancy are adversely affected if severe hypothyroidism is undiagnosed or inadequately treated. Thyroid function tests should be obtained during gestation in women taking T4 and appropriate dose adjustments should be made for TSH levels outside a normal range. The TSH-receptor blocking antibodies from the mother are a recognized cause of congenital hypothyroidism in the fetus and neonate that can be permanent or transient. If neonatal hypothyroidism is detected through neonatal screening programs, and prompt and adequate T4 replacement therapy is instituted as soon as possible following delivery, subsequent growth and development are usually normal. Paradoxically, pregnancy often has a favorable effect on the course of maternal Hashimoto's disease, although there is the risk of relapse postpartum. Pathophysiologic conditions of hCG secretion such as gestational trophoblastic disease and hyperemesis gravidarum may present as thyrotoxicosis in pregnancy, but the main cause of this syndrome is Graves' disease. The mainstay of treatment is antithyroid drugs and either propylthiouracil or methimazole may be used safely. Subtotal thyroidectomy, after medical control, is the alternative treatment, but radioiodine ablation is contraindicated.(ABSTRACT TRUNCATED AT 400 WORDS)

Female↗
PubMed1991

Regulation of insulin-like growth factor-binding protein messenger ribonucleic acid levels in sheep thyroid cells.

The insulin-like growth factors (IGFs) exist primarily bound to cell surface receptors or complexed to specific binding proteins (IGFBPs). The IGFBPs modulate the bioavailability of the IGFs and may enhance or inhibit IGF actions. Several distinct forms of IGFBPs have been described on the basis of size, immunological determinants, and distribution in biological fluids; the IGFBPs may differ as well in their biological function. Sheep thyroid cells produce IGFBPs under hormonal regulation. Cells grown in basal medium or with six-hormone (6H) medium supplements (transferrin, glycyl-histidyl-lysine, hydrocortisone, somatostatin, insulin, and TSH) release nonglycosylated BPs that migrate at 24, 27, 29, and 32 kDa on Western ligand blot. Cells cultured with the thyroid mitogens epidermal growth factor and phorbol ester release additional glycosylated IGFBPs of 40-44 kDa. Immunoprecipitation experiments indicate that 29- and 32-kDa IGFBPs are antigenically related to IGFBP-2, and the 40- to 44-kDa proteins are related to IGFBP-3. Using specific cDNA probes IGFBP-1, -2, and -3, we examined the regulation of IGFBP mRNA levels in sheep thyroid cultures. The rat IGFBP-2 cDNA probe hybridized to an approximately 1.6-kilobase mRNA species in cells under all culture conditions. However, IGFBP-3 mRNA was detectable only in epidermal growth factor- or phorbol ester-treated cells and appeared within 4 h, preceding the release of IGFBP-3 protein into the medium. The 6H additives, which stimulate differentiated function in thyroid cells, inhibited the mRNA levels of both IGFBP-2 and IGFBP-3. IGFBP-1 mRNA was not detectable. The distinct regulation of these IGFBPs suggest that they may play different biological roles in modulating thyroid physiology.

Actins↗
PubMed1991

Thyrotropin inhibits while insulin, epidermal growth factor and tetradecanoyl phorbol acetate stimulate insulin-like growth factor binding protein secretion from sheep thyroid cells.

Six insulin-like growth factor binding proteins (IGFBP) have been identified in the conditioned medium from sheep thyroid cells cultured under serum-free conditions. IGFBPs of 32, 28, 23 and 19 kDa were secreted by cells cultured for 14 days in serum-free and hormone-free medium. The constitutive secretion of IGFBP was inhibited by thyrotropin (TSH, 0.3 mU per mL). The effect was most marked on the secretion of the 28 kDa BP. High insulin concentrations stimulated the secretion of this IGFBP. The stimulatory effects of insulin were inhibited by TSH. Growth hormone treatment decreased the secretion of the 28 kDa protein. Tetradecanoylphorbol-13 acetate (TPA) and epidermal growth factor (EGF) both of which stimulate thyroid cell growth but inhibit differentiated function, markedly stimulated IGFBP secretion and induced the appearance of a 46 and a 150 kDa IGFBP. The effects of EGF and TPA were not identical. A rat IGFBP-2 cDNA reacted with sheep thyroid RNA of approximate size 1.6 kb. TPA treatment increased IGFBP-2 mRNA. Other hormones used to enhance differentiation and growth in thyroid cells in culture i.e. transferrin, somatostatin, cortisol and glycyl-histidyl-lysine acetate had no marked effects on IGFBP secretion nor on TSH-dependent, insulin-mediated iodide uptake and organification and cell growth. We show a correlation between secretion of high molecular weight IGFBP with enhanced growth but decreased function. Conversely, we find a correlation between decreased secretion of the 28 kDa BP and increased growth and function.

Animals↗
PubMed1991

TSH, IGF-1 and activated ras protein induce DNA synthesis in cultured thyroid cells.

TSH, IGF-1 and cellular ras genes have been proposed to function in thyroid cell transformation. Using cultured follicular cells, we demonstrate that TSH, IGF-1 and microinjected activated ras protein individually stimulate DNA synthesis. TSH-stimulated pathways include Gs at the plasma membrane and cyclic AMP response elements in the nucleus. The pathways and nuclear targets of IGF-1 and ras action appear at least partially distinct from those used by TSH.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

Interaction of TSH, insulin and insulin-like growth factors in regulating thyroid growth and function.

Primary cultures of sheep thyroid cells have been used to study regulation of thyroid growth and function by growth factors and TSH. Cells were plated at low density to minimize contributions from the endogenously produced insulin-like growth factors and their binding proteins and other proteins or hormones secreted by thyroid cells in culture. Growth of the cells was followed for 7-11 days in medium without serum. We found that TSH by itself was unable to stimulate thyroid growth. However, the ability of insulin and IGF-I to stimulate thyroid cell growth was markedly potentiated by TSH. Thyroid function was assayed by measurement of uptake of pertechnetate and organification of iodide and also by synthesis of thyroglobulin mRNA. TSH alone was unable to stimulate thyroid function appreciably. Insulin and IGF-I were ineffective by themselves at stimulating thyroid differentiated function, but in the presence of TSH, all indices were stimulated markedly. We conclude that TSH by itself is not a growth factor for thyroid cells. However, in the presence of insulin or IGF-I, TSH potentiates the growth-stimulating properties of this hormone. Similarly, TSH by itself does not stimulate thyroid function but requires the presence of insulin or IGF-I. These data show the cooperative interactions between growth factors and TSH in regulating both thyroid growth and function.

Animals↗
PubMed1990

Human thyroid cells transfected with SV40 DNA retain the TSH receptor.

Human thyroid cells were transfected with SV40 DNA using the calcium phosphate co-precipitation technique. The transfected cells grew rapidly and could be passaged readily. TSH and the immunoglobulin fraction from a patient with hyperthyroid Graves' disease stimulated adenylate cyclase activity in the transfected cells. These cells could potentially be used in clinical assays of patients' immunoglobulins without concern for species incompatibilities. On immunoblot analysis, extracts from SV40-transfected human thyroid cells, from sheep thyroid cells and from rat FRTL5 cells reacted with the immunoglobulin fraction from the patient with hyperthyroid Graves' disease but not with the immunoglobulin fraction from a pool of serum from normal subjects. Proteins of molecular weights 77,000, 70,000 and 54,000 were identified by the patient's immunoglobulin fraction in the three thyroid-derived cell types.

Cell Transformation, Viral↗
PubMed1989

Regulation of thyroperoxidase, thyroglobulin and iodide levels in sheep thyroid cells by TSH, tumor promoters and epidermal growth factor.

Using sheep thyroid cells in culture, we have studied the effects of thyroid stimulating hormone (TSH), epidermal growth factor (EGF) and the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) on the activity and expression of both thyroglobulin (Tg) and thyroid peroxidase (TPO) and on the ability of cells to trap and organify iodide. Using Western blotting techniques, we found that TSH increased the absolute cellular levels of Tg. The optimum TSH concentration for Tg mRNA production was between 0.1-1.0 mU/ml. Thyroglobulin mRNA levels were stimulated by TSH but detectable levels were also present in cultures grown in its absence containing cortisol, insulin, transferrin, somatostatin and glycyl-lysyl-histidyl acetate. Unlike Tg, TPO protein levels were found to be completely dependent upon TSH. A time course of TSH stimulation of TPO mRNA showed increases after 8 h of TSH stimulation, whereas induction of Tg mRNA by TSH was seen at 24 h. Iodide trapping and organification were also TSH-dependent processes, showing maximum activities at 300-500 muU/ml of TSH. The addition of 10 nM TPA caused a biphasic decrease in radiolabeled pertechnetate uptake, with complete inhibition being seen at 14 h. Inhibition of iodide organification occurred more rapidly. TPA and EGF (1 nM) reduced the amount of newly synthesized Tg in TSH-stimulated cells by 50% but the absolute amount of Tg within the cells was not markedly inhibited at these early times.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Characterization of insulin-like growth factor-binding proteins from sheep thyroid cells.

The insulin-like growth factors (IGFs) are bound by specific, high affinity binding proteins. Distinct classes of IGF-binding proteins have been described in human serum, amniotic fluid, cerebrospinal fluid, and conditioned medium from cultured cells. Sheep thyroid cells produce IGF-binding proteins under hormonal regulation. Cells grown without or with standard medium supplements (transferrin, glycyl-histidyl-lysine, hydrocortisone, somatostatin, insulin, and TSH) released binding proteins with apparent mol wt of 23, 29, and 32 kDa on Western ligand blot (nonreduced). Binding proteins from these cells appeared as 21, 26, 34, 36, and 41 kDa bands when cross-linked to [125I]IGF-I under reducing conditions. The addition of epidermal growth factor (EGF) or phorbol esters, thyroid cell mitogens stimulated the production of larger binding proteins with mol wt of 40-44 and 48-52 by ligand blot and cross-linking methods, respectively. Deglycosylation of conditioned medium cross-linked to [125I]IGF-I with endoglycosidase-F did not alter the size of the smaller binding proteins, but reduced EGF-stimulated binding proteins to 36-40 kDa. Similarly, tunicamycin treatment, which inhibits glycosylation, reduced only the size of this larger binding protein species. Polyclonal antisera directed against the human amniotic fluid binding protein (BP-28) immunoprecipitated the 32 kDa sheep thyroid binding protein seen on ligand blot and the cross-linked binding protein at 36-38 kDa. Antibody against the major human serum binding protein (BP-53) recognized only the larger EGF-stimulated binding proteins. In contrast to sheep thyroid cells, rat FRTL5 thyroid cells produced no detectable IGF-binding proteins. We conclude that the predominant binding proteins produced by sheep thyroid cells under standard culture conditions are non-glycosylated and immunoreact with antiserum directed against BP-28. EGF and phorbol esters stimulate production of larger glycosylated binding proteins antigenically related to BP-53.

Affinity Labels↗
PubMed1989

Lessons from the frozen North.

Presented in part as the Kaiser Foundation Distinguished Lecture at the annual meeting of the Western Association of Physicians, February 7, 1989.

Cost Control↗
PubMed1988

Insulin-like growth factors in sheep thyroid cells: action, receptors and production.

Sheep thyroid cells cultured in serum-free medium were used to study the biologic activity, binding, and production of the insulin-like growth factors (IGFs). IGF-I, IGF-II, and insulin stimulated thyroid cell division. Abundant, specific IGF receptors on sheep thyroid cell membranes were identified by binding displacement studies. Maximal specific binding of [125I]-labeled IGF-I and IGF-II to 25 micrograms of membrane protein averaged 21% and 27% respectively. The presence of type I and type II IGF receptors was confirmed by polyacrylamide gel electrophoresis of [125I]IGFs covalently cross-linked to cell membranes. Under reducing conditions, [125I]IGF-I bound to a moiety of approximate Mr = 135,000 and [125I]IGF-II to a moiety of approximate Mr = 260,000. Cross-linking of [125I]IGF-I to medium conditioned by thyroid cells indicated the presence of four IGF binding proteins with apparent Mr = 34,000, 26,000, 19,000 and 14,000. Thyroid cells also secreted IGF-I and II into the medium. IGF synthesis was enhanced consistently by recombinant growth hormone. These data indicate that sheep thyroid cells are a site for IGF action, binding, and production and provide further evidence that IGFs may modulate thyroid gland growth in an autocrine or paracrine manner.

Animals↗