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J Van Sande

Publications and source records attributed to J Van Sande.

At least 91 records · Page 5Linked to original sources
PubMed1987

Iodide-induced inhibition of adenylate cyclase activity in horse and dog thyroid.

The characteristics of the iodide-induced inhibition of cyclic AMP accumulation in dog thyroid slices have been previously described [Van Sande, J., Cochaux, P. and Dumont, J. E. (1985) Mol. Cell. Endocrinol. 40, 181-192]. In the present study we investigated the characteristics of the iodide-induced inhibition of adenylate cyclase activity in dog and horse thyroid. The inhibition of cyclic AMP accumulation by iodide in stimulated horse thyroid slices was similar to that observed in dog thyroid slices. The inhibition was observed in slices stimulated by thyroid-stimulating hormone, cholera toxin and forskolin. Increasing the concentration of the stimulators did not overcome the iodide-induced inhibition. Adenylate cyclase activity, assayed in crude homogenates or in plasma-membrane-containing particulates (100,000 x g pellets), was lower in homogenates or in particulates prepared from iodide-treated slices than from control slices. This inhibition was observed on the cyclase activity stimulated by forskolin, fluoride or guanosine 5'-[beta, gamma-imino]triphosphate, but also on the basal activity. It was relieved when the homogenate was prepared from slices incubated with iodide and methimazole. Similar results were obtained with dog thyroid. The inhibition persisted when the particulate fraction was washed three times during 1 h at 100,000 x g, in the presence of bovine serum albumin or increasing concentration of KCl. It was similar whatever the duration of the cyclase assay, in a large range of protein concentration. These results indicate that a stable modification of adenylate cyclase activity, closely related to the plasma membrane, was induced when slices were incubated with iodide. Iodide inhibition did not modify the affinity of adenylate cyclase for its substrate (MgATP), but induced a decrease of the maximal velocity of the enzyme. The percentage inhibition was slightly decreased when Mg2+ concentration increased, and markedly decreased when Mn2+ concentration increased. A detectable adenylate cyclase activity was demonstrated when intact slices were incubated in the presence of [alpha-32P]ATP, probably because of the presence of broken cells produced during the slicing. Iodide had no direct effect on this cyclase system, which confirms that iodide needs the integrity of the cell to induce the inhibition and suggests that the inhibition is not transmitted between cells.

Adenylyl Cyclase Inhibitors↗
PubMed1987

Tumor promoters as probes of protein kinase C in dog thyroid cell: inhibition of the primary effects of carbamylocholine and reproduction of some distal effects.

The acute effects of phorbol esters, used as probes of protein kinase C activation, were studied on dog thyroid slices incubated in vitro. The derivatives used were: tetradecanoylphorbol acetate (TPA), phorbol-12,13, didecanoate (PDD), phorbol-12,13-diacetate (PDA), and phorbol dibutyrate (PDBu) and as inactive controls, phorbol itself, phorbol-12, myristate and phorbol-13, acetate, in concentrations ranging from 5.10(-8) to 5.10(-6) mol/L. The active phorbol esters had no effect on basal cyclic AMP concentrations; they inhibited cyclic AMP accumulation induced by prostaglandin E1 but not that induced by thyrotropin (TSH) 1 mU/mL and forskolin 10 mumol/L. Phorbol esters like carbamylcholine acutely stimulated iodide organification and inhibited the stimulation of hormone secretion resulting from TSH, Cholera Toxin, forskolin, and Bu2-cyclic AMP action. These metabolic effects did not require the presence of extracellular Ca++, and could not be antagonized by Ca++ depletion or manganese addition. The active phorbol esters abolished the cyclic AMP independent increased PI turnover induced by TSH 10 mU/mL or carbamylcholine (Cchol) 10(-6) mol/L but did not affect the basal incorporation of 32P into phosphatidylinositol. They reduced the 45Ca efflux from preloaded slices below basal levels and blocked the increased 45Ca release induced by TSH and Cchol. They also inhibited the increase in cyclic GMP concentrations resulting from Cchol action but not the effect of the ionophore A23187 (10(-5) mol/L) nor the basal levels of cyclic GMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Alprostadil↗
PubMed1987

Dual activation by thyrotropin of the phospholipase C and cyclic AMP cascades in human thyroid.

In human thyroid slices prelabeled with myo-[2-3H]inositol, thyrotropin (TSH, 3-30 mU/ml) stimulated IP3, IP2 and IP1 generation over a prolonged time course. The cAMP response was much more sensitive to TSH, peaking between 1 and 5 mU/ml. Forskolin (10(-5) M) and isoproterenol had no effect on basal IP levels, while carbamylcholine (10(-5) M, 10(-4) M) also increased IP accumulation. These data suggest that in the human thyroid, TSH activates a phospholipase C generating IP3 and diacylglycerol independently of the well-known adenylate cyclase stimulation. They validate in the human model a dual mode of action of the hormone previously proposed on the basis of indirect observations.

Cyclic AMP↗
PubMed1987

Modulation of thyroglobulin release by dog thyroid slices.

Nonbutanol-extractable 131I (NBE131I) release by dog thyroid slices in vitro has been shown previously to be primarily thyroglobulin (Tg); it is stimulated by TSH. NBE131I (Tg) release has therefore been considered as an in vitro model of thyroglobulin secretion and was further characterized in this work. TSH-stimulated NBE131I (Tg) release, like TSH-stimulated BE131I (T4, T3 and iodide) release was reproduced by forskolin, an activator of adenylate cyclase. TSH-, (Bu)2cAMP- and forskolin-stimulated NBE131I (Tg) release was inhibited by 10(-5) M carbamylcholine, an effect relieved by 10(-5) M atropine, but not by 10(-4) M 1-methyl-3-isobutylxanthine. NBE131I (Tg) release was observed in the presence of 2 mM methimazole and 2 mM perchlorate. Cooling the slices to 20 degrees C or addition of 10(-5) M monensin completely blocked the formation of apical pseudopods and BE131I release but not NBE131I (Tg) release. Inhibition by 500 microM chloroquine of intralysosomal Tg hydrolysis and BE131I release did not enhance NBE131I (Tg) release. Cytochalasin B induced a concentration-dependent increase in basal and TSH-stimulated NBE131I (Tg) release at concentrations which depressed TSH-stimulated BE131I release. Removal of Ca2+ from the medium and slices by 10(-3) M or 10(-4) M EGTA increased NBE131I (Tg) release. In conclusion, in dog thyroid slices, TSH-stimulated NBE131I (Tg) release was mediated by cAMP and inhibited by 10(-5) M carbamylcholine at a step beyond cAMP. It was not neosynthesized Tg. It did not seem to require the formation of apical pseudopods or to result from the escape from lysosomes of undegraded thyroglobulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Modulation of cyclic AMP action in the dog thyroid by its agonist and antagonist Sp- and Rp-adenosine 3',5'-monophosphorothioate.

The diastereoisomeric forms of adenosine 3',5'-monophosphorothioate, Sp-cAMPS and Rp-cAMPS, have been shown to mimic and to inhibit activation of protein kinase type I and type II by cyclic AMP. In the present work, Sp-cAMPS mimicked thyrotropin (TSH) action on thyroid hormone secretion and protein iodination in dog thyroid slices, whereas Rp-cAMPS antagonized those effects. The phosphorothioates have been tested as inhibitors or activators of the three major phosphodiesterases: the Ca2+/calmodulin-sensitive form, the cyclic GMP-stimulated form and the cyclic AMP-specific enzyme. At 100 microM Sp-cAMPS inhibited the three enzyme activities. In contrast, Rp-cAMPS failed to stimulate activity of the three enzymes. From a comparison of the biological properties of Sp- and Rp-cAMPS and 3-isobutyl-1-methyl xanthine, it is suggested that one site of action of the phosphorothioates is on the cyclic AMP-dependent protein kinases, i.e. the effects of Sp-cAMPS and Rp-cAMPS observed in intact cell can be ascribed to the agonistic and antagonistic effects on the cyclic AMP-dependent protein kinases. However, partial inhibition of phosphodiesterase activities by the phosphorothioates cannot be excluded.

Animals↗
PubMed1986

The escape of cyclic AMP from dog thyroid slices exposed to positive and negative regulators.

Incubation of dog thyroid slices with 1 mU/ml TSH resulted in enhanced intracellular and extracellular cAMP accumulation. In the absence of TSH, the intra- and extracellular cAMP concentrations remained at a constant low level. The release of cAMP from TSH-stimulated slices was inhibited by 10 microM PGA1, 1 mM probenecid or 1 mM IBMX, which are known inhibitors of cAMP escape in several tissues. Negative controls of intracellular cAMP levels are exerted in the dog thyroid by 10 microM carbamylcholine (shown to activate a Ca++- calmodulin dependent phosphodiesterase), 100 microM norepinephrine and 100 microM iodide (both inhibiting adenylate cyclase activity). The purpose of the present study was to demonstrate that these three agents do not enhance cAMP escape. The results presented here show that these agents decrease both intracellular accumulation and escape in parallel. Moreover, the escape constants obtained by numerical simulation were not greater in the presence of inhibiting concentrations of carbamylcholine, norepinephrine or iodide. Thus the inhibition by these agents of cAMP accumulation in TSH-stimulated dog thyroid slices cannot be explained by a stimulation of cAMP escape from these cells.

1-Methyl-3-isobutylxanthine↗
PubMed1985

Transcriptional control of thyroglobulin gene expression by cyclic AMP.

Transcription of thyroglobulin (Tg) gene is under the positive control of thyrotropin (TSH). The mechanism of this control has been further investigated. Rats were treated with triiodothyronine (T3) to decrease their endogenous TSH production. Following the intravenous injection of bovine TSH, a 3-fold stimulation of Tg gene transcription could be detected in isolated nuclei as early as 1 h after treatment. The TSH effect was also observed in tissue fragments incubated in vitro under conditions where a concomitant stimulation of cAMP accumulation was detected. Forskolin, a universal activator of adenylate cyclase, was able to mimic TSH action on Tg gene transcription. We conclude that TSH controls transcription of Tg gene directly via its known interaction with receptors on thyrocytes and that cAMP is a physiological mediator of this effect.

Animals↗
PubMed1985

Islet-activating protein discriminates between different inhibitors of thyroidal cyclic AMP system.

TSH-induced cyclic AMP accumulation in dog thyroid slices is inhibited by norepinephrine through an alpha 2-adrenergic receptor, by carbamylcholine through a muscarinic cholinergic receptor, and by iodide. The inhibitory effect of iodide bears on the adenylate cyclase, but the exact mechanism of its action is still unknown. It is known that norepinephrine acts through activation of the Ni subunit of the cyclase, and that carbamylcholine, activating a phosphodiesterase, acts independently of Ni. IAP (islet-activating protein) has been shown to inactivate the Ni subunit. We studied the effect of IAP on the inhibitory action of iodide, norepinephrine, and carbamylcholine on cyclic AMP accumulation in TSH-stimulated thyroid slices. Incubations of 15 or 22 h, and relatively high concentrations of IAP (250 ng/ml) were necessary to demonstrate an effect of IAP on thyroid slices. We report here that, under those conditions, inhibition of cyclic AMP accumulation by norepinephrine, but not by carbamylcholine or iodide, was suppressed by IAP treatment. These results indicate that the cyclase inhibition by iodide, is either not mediated by Ni, or if mediated by Ni, involves a mode of regulation of this coupling protein that is different from that by which the other 'Ni-mediated' inhibitory hormones act on the enzyme.

Adenylate Cyclase Toxin↗
PubMed1985

Further characterization of the iodide inhibitory effect on the cyclic AMP system in dog thyroid slices.

Iodide inhibits cyclic AMP accumulation in the thyroid by a process which is prevented by inhibition of iodide uptake and of thyroid peroxidase. By a similar process, it also exerts other independent effects such as the enhancement of iodinated protein release. Iodide inhibited the stimulation of adenylate cyclase by prostaglandin E1, cholera toxin and forskolin. The action of iodide was not relieved by phosphodiesterase inhibitors and was not additive with the effect of norepinephrine or adenosine. Iodide did not decrease the cellular level of ATP. The data are compatible with an inhibition of adenylate cyclase beyond the level of the receptor, presumably at the level of the catalytic unit or its interaction with the positive transducing unit NS. The effect of iodide required TSH for its expression but not for its installation. It was decreased under all conditions in which iodide organification was decreased: decreased iodide or increased methimazole concentration, absence of calcium in the medium, etc. However, the relation between iodide binding to proteins and effect was not linear. The effect was not relieved by washing in the absence of iodide and in the presence of perchlorate, but it was partly reversible in the presence of methimazole propylthiouracyl or thiourea. It was not relieved by cooling to 20 degrees C and cytochalasin b, which block stimulated thyroglobulin hydrolysis and iodothyronine release, nor by actinomycin D, cycloheximide, puromycin, mepacrine or indomethacin. The data suggest that iodide binds to a saturable cell component by a reaction which is reversible only in the presence of thiol-containing drugs.

1-Methyl-3-isobutylxanthine↗
PubMed1984

Reduction due to ageing of TSH-stimulated thyroid hormone release in the cream hamster.

The in vitro secretion by thyroid lobes from young (2-month-old) and from "aged" (more than 21 months old) male cream hamsters was estimated by measuring the butanol-extractable 125I (BE-125I) released into the medium after 2 and 4 h of incubation in the presence or absence of thyroid stimulating hormone (TSH). Lobes were fixed at the end of incubation for examination by both light and electron microscopy. Other lobes from both groups were collected for estimation of cyclic AMP contents. BE-125I release by lobes from aged animals after TSH stimulation was significantly lower than that of young animals. Similarly, pseudopods resorbing colloid, the morphological markers of secretion, were much less prominent in the aged group than in the young group. As this observation and the reduced BE-125I release contrast with an equivalent increase of cyclic AMP in both the young and aged groups, it is suggested that the age-dependent defect resulting in reduced hormone secretion is located at a step beyond the generation of cyclic AMP in the cascade of events occurring between binding of TSH to plasma membrane receptors on the target cell and hormone release.

Aging↗
PubMed1984

Iodide organification defect in a cold thyroid nodule: absence of iodide effect on cyclic AMP accumulation.

A follicular adenoma of the thyroid was 'hot' one hour after 99mTc pertechnetate administration, but 'cold' 24 h after 131I iodide administration. Incubation of the tissue in vitro demonstrated a defect in iodide binding to proteins that was abolished by addition of an H2O2 generating system. In this tissue iodide failed to inhibit TSH-induced cyclic AMP accumulation. The results show that iodide oxidation is required for its inhibitory action on cyclic AMP accumulation in human thyroid.

Adenoma↗
PubMed1983

Effect of thyrotropin-releasing hormone on dog thyroid in vitro.

The in vitro action of thyrotropin-releasing hormone (TRH) on the cyclic AMP level and iodine metabolism in dog thyroid, has been studied. TRH inhibited cyclic AMP accumulation and subsequent secretion in slices stimulated by thyrotropic hormone (TSH), prostaglandin E1, cholera toxin and to a lesser extent forskolin. The effect of TRH was suppressed in a medium deprived of calcium or in the presence of isobutylmethylxanthine. TRH also stimulated iodide binding to proteins, but not cyclic GMP accumulation. Although all these characteristics of TRH action on dog thyroid fit those of prostaglandin F1 alpha in this tissue, TRH effects were not relieved by indomethacine. The possibility of a TRH action through other known inhibitors of the cyclic AMP system in dog thyroid such as: acetylcholine, alpha-adrenergic agents, adenosine, iodide were checked and ruled out. The possible involvement of other neurotransmitters, such as ATP or vasoactive intestinal peptide were studied but could not be substantiated. Our data suggest the existence of a direct negative action of TRH on the thyroid itself besides its stimulatory role at the pituitary level. The great variability of the TRH effect was overcome by pretreatment of the dog by pyridostigmine, an acetylcholinesterase inhibitor.

1-Methyl-3-isobutylxanthine↗
PubMed1983

Stimulation by forskolin of the thyroid adenylate cyclase, cyclic AMP accumulation and iodine metabolism.

Forskolin, a diterpene hypotensive drug, activates adenylate cyclase in brain and in some other tissues (Seamon et al., 1981). Forskolin activated adenylate cyclase in particulate preparations and enhanced cyclic AMP accumulation in slices of dog thyroid. These effects were maximal within minutes and remained constant afterwards. The action of forskolin on intact cells disappeared rapidly after washing. It reproduced two known cyclic AMP-mediated TSH effects: the activation of secretion and of protein iodination. Forskolin thus provides a very convenient tool for the study of the action of defined elevations of cyclic AMP level in thyroid cells. The activation by forskolin of adenylate cyclase was not reduced by Mn2+ which uncouples TSH and PGE1 action. This suggests that in the thyroid also, forskolin acts beyond the receptor level. The effect of forskolin on cyclic AMP accumulation was inhibited by the known negative regulators of this system in the thyroid, acetylcholine, iodide, norepinephrine, PGF1 alpha and adenosine. On the other hand, forskolin potentiated the effects of TSH, PGE1 and cholera toxin. These data show that, though it does not require the receptors for its action, forskolin does not uncouple them from the catalytic unit of adenylate cyclase.

Adenylyl Cyclases↗
PubMed1983

Immunocytochemical localization of protein kinases and calmodulin in dog thyroid cells.

By immunocytochemical methods, the protein effectors of known intracellular signal molecules were demonstrated in the thyroid follicular cell and their localization investigated. Cyclic AMP protein kinase subunit RII was clearly located in the nucleus. Protein kinase subunits RI and C were in the cytosol and on the apical membrane. Cyclic GMP kinase and calmodulin were mostly found in the cytoplasm and at the apical membrane; they were poorly represented in the nucleus. The only membrane underlined by several markers was the apical membrane, i.e. the site of iodination, oxido reduction and H2O2 generation.

Animals↗