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A Pontecorvi

Publications and source records attributed to A Pontecorvi.

52 records · Page 3Linked to original sources
PubMed1988

Selective degradation of mRNA: the role of short-lived proteins in differential destabilization of insulin-induced creatine phosphokinase and myosin heavy chain mRNAs during rat skeletal muscle L6 cell differentiation.

This investigation concerns the combined effects of removal and readdition of insulin and inhibition of protein and RNA synthesis on the stability of insulin-induced mRNAs during and after differentiation of rat L6A1 myoblast cells in culture. Addition of insulin accompanying the withdrawal of the mitogenic stimulus of serum to myoblasts caused an 80-fold increase in creatine phosphokinase (CK) activity which was largely accounted for by a similar increase in the amount of CK mRNA. The latter was co-ordinately induced with myosin heavy chain (MHC) mRNA but not malic enzyme (ME) mRNA. Measurements of steady-state levels of mRNA showed that removal of insulin caused CK mRNA, but not MHC mRNA, to be rapidly degraded, the effect being reversed upon readdition of the hormone. Direct measurement of 3H-labeled CK, MHC and beta-actin mRNAs confirmed the selective stabilization and destabilization of CK mRNA by the hormone. Conditions were established for a time-window during which cycloheximide (Cx) produced a virtually total arrest of protein synthesis in myotubes that was reversible upon removal of the inhibitor. Under these conditions, Cx selectively prevented the degradation of CK mRNA in a reversible manner. Actinomycin D (Act D) also arrested the loss of this mRNA. Under the same conditions of mRNA stabilization during de-induction, a superinduction of CK mRNA, but not MHC mRNA, was observed if the two inhibitors were added during induction in the continuous presence of insulin. We conclude that a short-lived protein(s), encoded by a short-lived mRNA(s), selectively regulates the stability of reversibly inducible mRNA.

Animals↗
PubMed1988

Insulin effect on thyroid hormone uptake in rat skeletal muscle.

Previous work has indicated that thyroid hormone entry into cells includes an energy-dependent, saturable process. In this study we investigated the effect of insulin on T3 uptake in rat skeletal muscle. Intact soleus muscles were preincubated for 30 minuted at 37 degrees C, pH 7.4, in modified Krebs-Ringer bicarbonate buffer in the presence or absence of insulin and then for 60 minutes after adding 50 pmol/L [125I] T3. The results showed a stimulatory effect of insulin that was half maximal at 33 nmol/L and maximal at 100 nmol/L. Addition of 10 mumol/L T3 to the incubation medium completely blocked the effect, showing that the action of insulin is exerted only on the specific component of T3 uptake. The substitution of extracellular sodium with an equimolar amount of lithium also prevented the insulin effect. [125I] T4 uptake was unaffected by insulin. These results indicate that T3 uptake in skeletal muscle is sensitive to insulin, that insulin stimulates the specific component of T3 uptake in a dose-dependent manner, and that its action requires extracellular sodium. In contrast, T4 uptake is insensitive to insulin action in accordance with previous results that indicated passive diffusion as its major pathway for cell entry.

Age Factors↗
PubMed1988

Different intracellular and intranuclear transport of triiodothyronine enantiomers in rat skeletal myoblasts.

The mechanism(s) responsible for the different biological potency of L- and D-T3 was investigated in rat L6E9 myoblasts. After incubation with intact cells at 37 C L-T3 cellular and nuclear uptakes were 91% and 70% higher than those of D-T3, respectively, but values for nuclear uptake as a fraction of cellular uptake were similar. The difference between the enantiomers was abolished at 4 C, and metabolic and endocytotic inhibitors reduced nuclear and extranuclear saturable uptake of L-T3 to a similar degree, but had little or no effect on D-T3 uptake. The affinity constants (Ka) for L- and D-T3 binding to isolated nuclei were similar, but the apparent nuclear Ka of L-T3 in intact cells was 5-fold greater than that of D-T3. The findings suggest that stereospecific transport, mainly active at the plasma membrane, occurs in rat skeletal muscle cells. This discriminative pathway of cell entry facilitates L-T3 uptake by an energy-dependent pathway not shared by D-T3 and may explain the greater potency of L-T3 than D-T3.

Animals↗
PubMed1987

Intracellular transport of 3,5,3'-triiodo-L-thyronine in rat skeletal myoblasts.

Since in skeletal muscle circulating L-T3 is the only source for the hormone bound to nuclei, we investigated the intracellular and intranuclear transport of L-T3 in L6E9 rat skeletal muscle cells. The characteristics of this process were assessed by analyzing the nuclear bound L-T3 as a marker of the internalized hormone and by determining the initial rate of L-T3 uptake. [125I]L-T3 cellular uptake at 37 C reached a plateau at 2 h when the nuclear uptake, after an initial lag phase, was still increasing and represented 4.7% of the cellular uptake. Incubation at 4 C caused [125I]L-T3 cellular uptake to decrease by 77% and nuclear uptake to be abolished. A similar effect on [125I]L-T3 nuclear uptake was obtained after myoblasts were incubated at 37 C with a 1000-fold excess of unlabeled L-T3. The addition of various inhibitors of ATP production, cytoskeleton integrity, endocytosis, and Na+, K+-ATPase that did not interfere with [125I]L-T3 binding to the cell surface or to isolated nuclei caused a dose-dependent reduction of both extranuclear and nuclear uptake, ranging from 34-85%. Scatchard analysis revealed the presence on the myoblast surface of L-T3 high affinity (Ka = 1.6 X 10(9) M-1) and low affinity (Ka = 5.4 X 10(6) M-1) binding sites; other iodothyronines exhibited lower affinity for both sites. Kinetic analysis of L-T3 transport after 60-sec incubation at 23 C defined a process with a Km of 17 +/- 5.6 nM and a maximum velocity of 83 +/- 35 pmol/mg DNA. These results indicate the existence in rat myoblasts of a temperature-dependent, energy-requiring, saturable, and stereospecific L-T3 uptake mechanism, probably mediated through an endocytotic pathway, located on the myoblast plasma membrane, that may regulate L-T3 action in skeletal muscle.

Animals↗
PubMed1986

Energy-dependent uptake of 3,5,3'-triiodo-L-thyronine in rat skeletal muscle.

The uptake of [125I]T3 in rat skeletal muscle was investigated by incubating intact soleus muscles with a tracer amount of [125I]T3. At 37 C [125I]T3 uptake increased asymptotically; at 60 min the muscle contained 10% of the total [125I]T3 or 0.238 +/- 0.021% per mg wet tissue. At 0 C the [125I]T3 uptake was 1/5 of that at 37 C. The specific [125I]T3 uptake, determined by subtracting the uptake in the presence of 10 microM unlabeled T3 from the total [125I]T3 uptake, attained a plateau after 60 min. Washout experiments, done by first incubating the muscle for 60 min at 37 C or 0 C with [125I]T3 and then at 0 C for 3 h with unlabeled T3, showed that 21 +/- 2% or 58 +/- 4% of the radioactivity, respectively, was released, indicating an intracellular location of the hormone after incubation at 37 C. Addition of increasing concentrations of L-T3, D-T3 and L-T4 caused a progressive inhibition of the [125I]T3 uptake; the 50% inhibitory concentrations being 400 nM, 7 microM, and more than 15 microM, respectively. Preincubation of soleus muscles with metabolic inhibitors almost completely inhibited [125I]T3 specific uptake, with oligomycin and antimycin causing 98 +/- 4% and 81 +/- 3% reduction, respectively. Monodansylcadaverine and bacitracin, inhibitors of receptor-mediated endocytosis, reduced the specific [125I]T3 uptake in a dose-dependent manner up to 67 +/- 3% and 62 +/- 2%, respectively. These results indicate the presence of a saturable, stereospecific, and energy-dependent process responsible, at least in part, for T3 uptake in rat skeletal muscle. This specific T3 uptake may be a receptor-mediated endocytosis process.

Animals↗
PubMed1984

Lack of inhibition of anterior pituitary hormone release during chronic treatment with calcium antagonists.

Calcium antagonists are widely used for the treatment of cardiovascular disorders, especially ischaemic heart disease. It has been demonstrated that these drugs, either in vitro or acutely administered in humans, inhibit the basal and stimulated secretion of pituitary hormones by blocking calcium influx through slow calcium channels. To see if a similar effect could be detected after their chronic administration, we studied the basal, TRH- and LHRH-stimulated TSH, PRL, LH and FSH release in 18 male subjects with chronic stable angina before and on the 30th day of oral treatment with verapamil (n = 8;80 mg three times a day) or with nifedipine (n = 10; 10 mg three times a day). Neither drug had any effect on basal TSH, PRL, LH and FSH values or on their response to the specific hypothalamic-releasing hormones. These results suggest that the chronic administration of calcium antagonists, at the usual therapeutic doses, does not effect the process of stimulus-secretion coupling of anterior pituitary hormones, ruling out any impairment of the related target glands which have been expected on the basis of previous studies.

Aged↗
PubMed1984

Transitory subclinical and permanent hypothyroidism in the course of subacute thyroiditis (de Quervain).

Sixty-two patients affected with subacute thyroiditis (SAT) were followed for a mean period of 14 months (range 1-40), by monitoring thyroid hormone levels in basal condition, pituitary TSH reserve, antithyroglobulin (TgAb) and antimicrosomal antibodies ( MsAb ), in order to study the natural course of the disease and to characterize its intermediate phase. In the first phase the mean serum iodothyronine levels were within normal limits, nevertheless elevated T3 and T4 levels were detected in 34 (54%) and 20 (32%) patients, respectively. The next phase was characterized by normal serum iodothyronine levels; TRH stimulation test, however, showed a significant increase of pituitary TSH reserve in 35 (56%) patients. All parameters reverted gradually towards normal in all but 3 patients, who showed overt permanent hypothyroidism. TgAb and MsAb were positive in the early stage in 15 (24%) and 40 (64%) patients, respectively, disappearing at the end of the follow-up period in all but one patient; this particular patient belonged to the group of 3 patients affected with permanent hypothyroidism. Our data indicate that the onset of SAT is characterized by transient hyperthyroidism and that transient subclinical hypothyroidism characterizes the next phase. TRH stimulation test is required for the diagnosis of the latter and for the identification of the few who develop permanent hypothyroidism.

Adolescent↗
PubMed1982

[Inhibition of the biosynthesis of thyroglobulin with propranolol in the rat].

Thyroglobulin biosynthesis was studied in thyroid glands of rats treated during 30 days with a daily dose of propranolol, a non-selective beta-adrenergic blocking drug. Studies were carried out by extraction of soluble proteins from homogenates after incubation of the glands in presence of [3H]-4,5-L-leucine and [3H]-D-1-galactose. Thyroglobulin 19S, 12S and 4-8S soluble proteins were separated and identified by ultracentrifugation in a saccharose gradient. The glands of rats treated with propranolol showed a decreased amount of soluble proteins as well as a decreased incorporation of [3H] labeled markers. 19S thyroglobulin is poorly represented, but very large amounts of the 12S monomer are present; this suggests an impairment in the dimerization of the 12S subunit, absent in normal controls. This impairment could be due to a structure modification. Propranolol reduces the biosynthesis of thyroglobulin in thyroid gland as well as the formation of T3 from T4 in peripheral tissues; its therapeutical use against thyrotoxicosis is thus justified. The study of its action on the dimerisation of the 12S subunit could be of interest to clear the mechanism of thyroglobulin biosynthesis.

Animals↗
PubMed1982

[Inhibition of the biosynthesis of thyroglobulin in the thyroid gland of rats by isoniazid].

Groups of rats have been treated for one month with a daily dose of 50 mg/kg of body weight/day of isoniazide a product used therapeutically in man against tuberculosis. The animals submitted to this experiment showed an increase of thyroid weight (39%) and a decrease of its content in water soluble proteins, including thyroglobulin and precursors. These proteins have been labeled in vitro by [3H]-4,5-L-leucine and by [3H]-galactose, by incubation of isolated glands during 4 h in a medium containing this labeled marker. The decrease of thyroglobulin-like proteins was of 20-37% for [3H]-D-1-galactose, labeled fraction and of 46-53% for the [3H]-leucine labeled fraction. Two thirds of the radioactive protein sedimented by ultracentrifugation in a sucrose gradient were present in a 12S monomer of thyroglobulin. This suggests an impairment of biosynthesis of 19S thyroglobulin, in which two of the subunit are associated. Under experimental conditions adopted this 19S protein was labeled by [3H]-leucine, but not by [3H]-galactose. Two other antituberculous agents studied, ethambutol and rifamizine, exerted not the same effects on thyroid gland in rats. Therefore a control of thyroid function appear to be necessarily only in man treated by isoniazine.

Animals↗
PubMedDate not supplied

Molecular genetics of benign thyroid disease.

Thyroid diseases include forms amenable to alterations in genes involved in functional regulatory processes, morphofunctional development, hormogenesis and hormone functional expression. A number of genetic diseases are consequent of a point mutation, the cause of the replacement of a single nucleotide which may alter the chromosome number structure and morphology. Among structural anomalies there is deletion, duplication, inversion, translocation and isochromosome formation. Among thyroid diseases, the underlying cause of some of them is represented by alterations in genes regulating the thyroid function, alterations in genes of thyroid differentiation. Less common are the alterations in genes connected with the synthesis of proteins involved in hormone transport while alteration in genes encoding thyroid hormone receptors and in genes involved in thyroid neoplastic transformation are extensively described in literature. The studies of molecular biology will allow in-dept knowledge of the pathogenesis of thyroid disease associated to genetic alterations.

Chromosome Aberrations↗
PubMedDate not supplied

Molecular biology of thyroid neoplasms.

Thyroid tumorigenesis proceeds through the progressive accumulation of alterations in genes involved in the regulation of cell proliferation and differentiation accompanying the acquisition of phenotypic, biological and clinical characteristics of increasing malignancy and dedifferentiation. The molecular alterations specific to thyrocyte carcinogenesis are examined. Ras mutations seem to represent an early occurrence in thyroid tumorigenesis being common to both benign and malignant follicular tumors; they would represent the early mutational events able to enhance the cell proliferation. Subsequent alterations in several genes will probably result in the determination of a follicular or papillary phenotype. In particular, mutational events activating ret, met and trk thyrokinase receptors direct the tumor growth and development towards the papillary type. Progression towards a follicular phenotype would instead occur in two stages: first there is the loss of function of genes on chromosome 11q13 which may direct the tumor cell towards the phenotype of follicular adenoma, second, there is the inactivation of the probable suppressor oncogene on chromosome 3p which might be fundamental in the transition from adenoma to follicular carcinoma. Undifferentiated or anaplastic tumors are characterized by the presence of p53 gene mutations.

Cell Division↗
PubMedDate not supplied

Clinical and laboratory follow-up in differentiated thyroid carcinoma.

Thyroid carcinoma is the most frequent endocrine malignant neoplasm even if a rare occurrence (0.5%-1.0%) of all human malignant tumors. Primary differentiated (papillary and follicular) forms represent over 90% of the total. Since recurrence of thyroid carcinoma can occur even after several years, patients must undergo a life-long follow-up. Thyroglobulin, being organ-specific, plays a major role as tumor marker and it is used essentially in the monitoring and follow-up of patients with differentiated thyroid carcinoma, both during L-thyroxine suppressive therapy and when it is discontinued or after recombinant TSH administration. The presence of antithyroglobulin antibodies masks the real value of thyroglobulin and therefore, at the same time, antithyroglobulin antibodies should always be determined.

Algorithms↗
PubMedDate not supplied

Hyperthyroidism with concurrent thyroid cancer.

The occurrence of thyroid malignancy is considered a rare event in hyperthyroid patients. With the aim of assessing the clinical relevance of this association, we have analyzed the incidence of thyroid cancer in hyperthyroid patients treated by surgery. The incidence of thyroid cancer was retrospectively evaluated in 202 hyperthyroid patients who underwent thyroidectomy during a twenty-year period. A thyroid cancer was diagnosed in 12 cases (5.9 per cent). Histologic examination revealed the presence of papillary carcinoma in 9 cases, follicular carcinoma in 1 case and Hürthle cell carcinoma in 2 cases. The association between thyroid cancer and hyperthyroidism was more frequent in toxic adenomas (17.8 per cent) than in toxic diffuse (5.3 per cent) or multinodular goiters (1.7 per cent). In 8 patients they presented as an occult carcinoma (maximum diameter below 1 cm), but unfavourable histologic features, such as local invasiveness and multifocality, were found in 5 of them. Follow-up data indicate that all 12 patients are currently alive and apparently free of disease. Hyperthyroid patients, particularly those affected by toxic adenomas, should be carefully evaluated to exclude the presence of concurrent malignancy. A special attention should be made moreover to the presence of "occult" lesions that, in our study was characterized in a higher proportion (62.5 per cent) of cases, by unfavourable histologic features.

Adult↗
PubMedDate not supplied

Growth hormone in inflammatory bowel disease.

Crohn's disease and ulcerative colitis are inflammatory diseases of the gastrointestinal tract characterized by chronic relapsing inflammation and catabolism. Growth hormone/insulin-like growth factor-I axis is important in inflammatory bowel disease, because of the effects on epithelial cell kinetics, collagen deposition and immunomodulation. The potential of growth hormone as a therapeutic option in inflammatory bowel disease has been proven in various clinical settings. Acquired growth hormone resistance in inflammatory bowel disease seems to be mediated by a combination of undernutrition and active inflammation. In particular, proinflammatory cytokines, such as TNF-a and interleukin-6, have been implicated as potential mediators of growth hormone resistance. The introduction of anti-TNF-alpha monoclonal antibodies has proven very efficacious in patients with inflammatory bowel disease. By reducing cytokines levels in inflammatory cells of intestinal mucosa, infliximab could interfere with cytokine-induced growth hormone resistance. Recent in vivo data have shown that acquired growth hormone resistance in patients with inflammatory bowel disease may be reversed after the administration of anti-TNF-alpha therapy.

Animals↗