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R Gärtner

Publications and source records attributed to R Gärtner.

At least 73 records · Page 4Linked to original sources
PubMed1990

Evidence that an iodolactone mediates the inhibitory effect of iodide on thyroid cell proliferation but not on adenosine 3',5'-monophosphate formation.

Iodolactone (6-iodo-8,11,14-eicosatrienoic-delta-lactone), an iodinated derivative of arachidonic acid, was found to be synthesized in rat thyroid slices; however, the physiological role of this compound is still unknown. We tried to detect iodolactone in isolated porcine thyroid follicles and investigated the effects of in vitro synthesized iodolactone on epidermal growth factor-induced thyroid cell proliferation and TSH-induced cAMP formation. In vitro synthesis of iodolactone was performed with lactoperoxidase-catalyzed iodination of arachidonic acid in the presence of trace amounts of [125I]- and [3H]arachidonic acid. After purification by silica gel chromatography, HPLC of the reaction products revealed one main peak containing trace amounts of both [125I]- and [3H]arachidonic acid. With gas chromatography-mass spectrometry (GC-MS) a molecular mass of 391 m/z, corresponding to the derivatization product of iodolactone, was found. An ethanol-chloroform extract of isolated thyroid follicles preincubated with KI (10 microM) and arachidonic acid (1 microM) revealed peaks in HPLC and GC comparable with those of in vitro synthesized iodolactone. This indicates the ability of thyroid follicles to form iodolactone. Iodolactone (0.1-1.0 microM) dose-dependently inhibited epidermal growth factor-induced thyroid cell growth. This growth-inhibiting effect of iodolactone was 50-fold more pronounced than the inhibitory effect of KI (4 X 10(-5) microM) on thyroid cell proliferation. In contrast to the effect of iodide, the inhibitory effect of iodolactone on thyroid cell growth could not be abolished by methimazole (1 mM). Basal as well as TSH (0.5 U/liter)-induced cAMP formation were not changed by iodolactone. These experiments suggest a physiological role of iodolactone as a mediator of the known inhibitory effect of iodide on thyroid growth.

Animals↗
PubMed1990

Advances in pathogenesis of goitre.

Growth regulation of the thyroid has been reinvestigated using an ex vivo system of isolated porcine thyroid follicles. Not only the direct effect of TSH, EGF, IGF I as well as iodine on growth of these follicles has been investigated but also the paracrine communication of these follicles with endothelial cells and fibroblasts. The results of recently published investigations with this culture system are summarized in this article. We could demonstrate that IGF I and EGF have a dose related effect on thyroid cell proliferation, whereas TSH has no effect on thyroid cell growth, if the iodine content of follicles is kept normal. Saturation of thyroid follicles with increasing amounts of iodine (1-40 microM K1) inhibit dose dependent EGF, IGF I or fetal calf serum induced thyroid cell proliferation. Inhibition of iodide organification with PTU or MMI abolish the growth inhibitory effect of iodide indicating that an organified iodinated product is responsible for the growth inhibitory effect of iodide on thyroid cell proliferation. Thyroid follicles secrete a FGF like substance which stimulates the growth of fibroblasts as well as endothelial cells. The secretion of FGF into the culture medium is decreased during TSH stimulation and enhanced during stimulation with EGF. The pretreatment of follicles with iodide abolishes the growth promoting effect of conditioned medium from thyroid follicles on fibroblasts and endothelial cells. We conclude that local growth factors like IGF I and EGF are responsible for thyroid cell proliferation whereas TSH stimulates specific function and hypertrophy of thyroid cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Evidence that thyroid growth autoregulation is mediated by an iodolactone.

For further investigating the mechanism of the known autoregulation of thyroid follicle growth and function by iodine, we tried to detect iodolactone (6-iodo-8,11,14-eicosatrienoic-delta-lactone) in isolated porcine thyroid follicles and investigated the effects of in vitro synthesized iodolactone on EGF induced thyroid cell proliferation as well as on TSH induced cycli AMP formation. In vitro synthesis of iodolactone was performed with lactoperoxidase catalyzed iodination of arachidonic acid. With gas chromatography-mass spectrometry a molecular mass of 391 m/z corresponding to the derivatization product of iodolactone was found. An ethanol/chloroform extract of isolated thyroid follicles preincubated with KI (10uM) and arachidonic acid (1uM) revealed an identical substrate. This indicates the ability of thyroid follicles to form iodolactone. Iodolactone (0.1-1.0 uM) dose-dependently inhibited EGF induced thyroid cell growth. This growth inhibiting effect of iodolactone was found to be 50-fold more pronounced than the inhibitory effect of KI (4 x 10(-5] on thyroid cell proliferation. In contrast to the effect of iodide, the inhibitory effect of iodolactone on thyroid cell growth could not be abolished by methimazole (1mM). The basal as well as TSH (0.5 U/l) induced cyclic AMP formation was not changed by iodolactone. These experiments suggest a physiological role of iodolactone as a mediator of the known inhibitory effect of iodide on thyroid growth.

Animals↗
PubMed1990

Growth regulation of porcine thyroid follicles in-vitro by growth factors.

Primarily intact thyroid follicles were isolated from explanted thyroid glands of hogs immediately after sacrifice. These intact thyroid follicles had a preserved polarity, still contained thyroglobulin, could be liberated from contaminating mesenchymal single cells and could be kept in culture for at least 14 days. They respond to bovine TSH (1 mU/ml) with a 10-fold increase in cAMP production within 15 min, trapp and organify iodine and secrete thyroid hormones. In contrast to thyroid monolayers, prepared from these thyroid follicles, intact thyroid follicles did not proliferate in response to bTSH (1-1000 uU/ml) stimulation. When thyroid follicles, however, were stimulated with EGF (1-5 ng/ml) a dose dependent increase in cell number as well as [3H]-thymidine incorporation into acid precipitable DNA was seen. The growth response of thyroid follicles to EGF (5 ng/ml) in comparison to thyroid monolayer cells was 275% versus 145% increase in cell number within 6 days. With IGF I, a proliferative response of thyroid follicles was found, and this was synergistic with simultaneous incubation with EGF. When thyroid follicles were incubated with EGF together with TSH, a dose dependent inhibition of [3H]-thymidine incorporation as well as cell number with increasing amounts of TSH (1-1000 mU/ml) occurred. The comparable effect was found, when thyroid follicles were stimulated to growth with IGF I (100 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Release of an endothelial cell growth factor from cultured porcine thyroid follicles.

It has been proposed from in vivo studies that thyroid angiogenesis during thyroid enlargement may be due to paracrine mitogenic factors released by epithelial thyroid cells. To study this paracrine growth regulating communication between thyroid cells and endothelial cells in vitro, culture medium from isolated porcine thyroid follicles was investigated for a growth promoting effect on porcine aortal endothelial cells. Serum-free conditioned medium (CM) from thyroid follicles in suspension culture contains a dose-related mitogenic activity which stimulates endothelial cell growth up to 197%. Stimulation of the thyroid follicles with TSH (1 mU/ml) significantly reduced the mitogenic activity for endothelial cells in CM to 131%. Thyroid hormones had no influence on mitogenic activity in CM. When follicles were treated with iodide (20 microM) during CM production, no proliferation of endothelial cells was observed by this CM. In contrast, CM from epidermal growth factor-treated thyroid follicles significantly enhanced the mitogenic activity for endothelial cells up to 235%. The mitogenic activity was precipitable by saturated ammonium sulfate, showed high affinity to heparin by chromatography on heparin-sepharose, and was abolished after treatment of CM with trypsin. On gel electrophoresis the heparin-binding fraction showed a double band with a mol wt of 15 and 15.5 k. These data show a paracrine mitogenic activity on endothelial cells released by thyroid follicles which is regulated by TSH, epidermal growth factor, and iodide in parallel with the direct effect of these substances on thyroid cell growth. The data suggest that the mitogenic factor is a polypeptide, which belongs to the heparin-binding growth factors.

Animals↗
PubMed1987

Evidence that thyroid growth promoting activity of immunoglobulin preparations is due to contamination with EGF.

Immunoglobulin (IG) preparations may be contaminated with growth factors. Therefore, we investigated whether the growth promoting activity in IG preparations (thyroid growth stimulating immunoglobulins = TGI) from patients with sporadic goitre may be caused by contaminating EGF (epidermal growth factor). EGF in sera as well as in indifferently prepared IG of patients with recurrent goitre (n = 23), Graves' disease (n = 19) and normals (n = 17) was determined by EGF receptor assay. Comparatively, the ability for stimulating thyroid cell growth was determined in these IG preparations (2 mg/ml). EGF in ammoniumsulphate (AS) precipitates was about 2-fold higher than serum EGF. The growth promoting activity of indifferent IG preparations correlated with the EGF content. After additional purification on protein A-sepharose, neither EGF, nor a growth promoting activity was found in these IG preparations. We therefore conclude, that the growth promoting activity of crude IG preparations may be due to a contamination with EGF.

Animals↗
PubMed1987

Hypertrophy and hyperplasia during goitre growth and involution in rats--separate bioeffects of TSH and iodine.

Goitre growth was investigated in rats receiving a low iodine diet (less than 0.1 microgram iodine/g) and either 1 g/l KClO4 or 1 g/l propylthiouracil (PTU), or a combination of KClO4 or PTU with 50.82 nmol/1 T3 in tap water for 3 weeks. To investigate goitre involution, rats with iodine-deficient goitres were treated for 3 weeks either with T3 (0.5 microgram T3/day = 0.768 nmol/day), iodide (0.5 or 2.7 micrograms KI/day) or a combination of T3 with both iodide doses. Histology together with total DNA distinguished between hypertrophy and hyperplasia of the gland. During goitre growth there was highly significant correlation between goitre weight and TSH serum level (r = 0.93, P less than 0.001). Thyroid total DNA, however, was only weakly correlated to TSH but was inversely related to the degree of iodine deficiency. During goitre regression, TSH levels were normalized, histological signs of hypertrophy had disappeared, and thyroid weight was nearly normalized in all therapy groups. Total DNA, however, was normalized only with 2.7 micrograms KI/day (95 +/- 18 micrograms DNA/gland), and still elevated in all other groups. The highest DNA levels were found under T3 therapy (143 +/- 21 micrograms DNA/gland) and under 0.5 microgram KI/day (161 +/- 19 micrograms DNA/gland). Reduction of total DNA was independent of TSH, but followed replenishment of the iodine content of the glands. We conclude that TSH mainly induces hypertrophy, whereas thyroid hyperplasia is mainly regulated by the intracellular iodine content.

Animals↗
PubMed1987

Inhibition of cAMP formation by EGF in thyroid follicles is mediated by intracellular Ca++.

The mechanism of cAMP-inhibition by EGF was studied in isolated porcine thyroid follicles. EGF inhibited TSH-induced cAMP-formation maximally by 40%, this effect remained up to 1 h of pre-incubation. The calcium-ionophore A 23 187 also inhibited cAMP-formation, but its effect was relieved after 1 h. The phorbolester TPA had a biphasic influence on cAMP-formation, with a transient increase (5 min) before a sustained inhibition (60 min); the inhibitory effect was mimicked by the diacylglycerol 1-oleoyl-2-acetyl-glycerol. Exogenous arachidonic acid had only a small and transient inhibitory effect on cAMP-formation. We conclude, that EGF inhibits cAMP-formation by a raise of intracellular Ca++, as well as by the direct activation of proteinkinase C, indicating, that a phosphorylated product could be a mediator for the inhibition of adenylate cyclase.

Animals↗
PubMed1987

Paracrine interaction between thyrocytes and fibroblasts.

Cell free supernatants (conditioned medium) of isolated porcine thyroid follicles, stimulated with EGF (5 ng/ml) or TSH (1-1000 microU/ml), were tested for a mitogenic activity for fibroblasts. Whereas TSH-conditioned medium dose-dependently stimulated [3H]thymidine incorporation into DNA of fibroblasts, only a weak stimulation was found with EGF. However, when the changes in cell number were determined, a significant increase was only found with EGF-conditioned medium from thyroid follicles. The cause of this discrepancy is a dose-dependent stimulation of [3H]thymidine incorporation into fibroblasts by cAMP and thyroid hormones. Cyclic AMP, however, does not stimulate growth of fibroblasts. IGF I production is stimulated in fibroblasts by basal as well as EGF stimulated conditioned medium of thyroid follicles. In contrast, TSH-conditioned medium inhibited IGF I production in fibroblasts. Conditioned medium itself is free of detectable IGF I. As IGF I stimulates not only growth of fibroblasts, but also of thyrocytes, we conclude, that conditioned medium from thyrocytes stimulates IGF I production in fibroblasts, which itself stimulates fibroblast and thyrocyte growth.

Animals↗
PubMed1986

Inherited thyroxine-binding globulin excess. Study in a kindred.

A three-generation family with hereditary high thyroxine-binding globulin (TBG) serum levels has been studied. All patients were clinically euthyroid and did not have a goiter. Four females of the eleven members of the kindred had elevated TBG (range: 34-56 micrograms/ml), total thyroxine (T4) and total triiodothyronine (T3) levels, but normal free T4 (fT4) and normal response of thyroid stimulating hormone (TSH) to intravenous application of thyrotropin-releasing hormone (TRH). Microheterogeneity of TBG studied by isoelectric focusing showed a normal pattern. No variations of the four main bands as seen in other causes of TBG excess like liver diseases, estrogen therapy or pregnancy could be measured. The changes in TBG concentration seem to be due to an abnormal gene expression controlling synthesis of TBG.

Adolescent↗