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Biomedical subjects

B Rapoport

Publications and source records attributed to B Rapoport.

At least 217 records · Page 12Linked to original sources
PubMed1981

Prevention by nicotinamide of desensitization to thyrotropin stimulation in cultured human thyroid cells.

The presence of 50 mM nicotinamide together with 100 milliunits/ml of TSH in the incubation medium prevented the decline in human thyroid cell cAMP from maximum, stimulated levels (15-30 min) that occurs when the cells are exposed to TSH alone. Nicotinamide in the absence of TSH did not increase thyroid cell cAMP content. TSH desensitization, and its prevention by nicotinamide, occurred in the presence or absence of 3-isobutyl-methylxanthine. 1-Methyl nicotinamide and N'-methyl nicotinamide similarly prevented TSH desensitization. Recovery from TSH desensitization was prolonged and incomplete after 72 h. The presence of 50 mM nicotinamide hastened recovery from desensitization. Desensitization of the cAMP response to 10(6) M prostaglandin E1 and 1 mM adenosine was unaffected by nicotinamide. Other inhibitors of poly(ADP-ribose) polymerase activity, 5-bromouridine, 5-bromo-2'-deoxyuridine, and thymidine (all at 50 mM) completely or partially prevented TSH desensitization. Pyridoxine (50 mM) similarly prevented this phenomenon. As with dog thyroid cells, 10(-4) M cycloheximide blocked TSH desensitization. The combination of 10(-4) M cycloheximide and 50 mM nicotinamide had a synergistic effect in augmenting the thyroid cell cAMP response to TSH stimulation.

Cells, Cultured↗
PubMed1981

Hormonal stimulation of eucaryotic cell ADP-ribosylation.

The effect of thyrotropin (TSH) on the ADP-ribosylation of endogenous thyroid cell acceptor proteins was examined. Cells were "permeabilized" at 4 degrees C in hypotonic medium and then exposed to [(32)P]- or [(3)H-adenine]NAD(+). The net incorporation of labeled ADP-ribose was measured by trichloroacetic acid precipitation. TSH (100 mU/ml) enhanced ADP-ribosylation with a maximum effect after 30-60 min in the majority of experiments. TSH stimulation was observed even when the incubation contained 1,000-fold more exogenous NAD(+) than the amount of NAD(+) contributed by the permeabilized cells, indicating an effect on enzymatic activity rather than an alteration in NAD(+) pool size or specific activity. No incorporation of radioactivity from labeled NAD(+) was observed in cells not rendered permeable to NAD(+) by hypotonic shock. TSH did not increase the rate of disappearance of trichloroacetic-precipitable radioactivity and did not contain intrinsic NAD(+) glycohydrolase activity. Alkali and snake venom phosphodiesterase, but not ribonuclease or deoxyribonuclease digestion of trichloroacetic acid precipitable thyroid cell radioactivity, revealed primarily 5'-AMP, consistent with an effect of TSH on mono-ADP ribosylation. Nicotinamide and thymidine (50 mM) inhibited both basal and TSH-stimulated ADP-ribosylation of thyroid cell protein. Dibutyryl cyclic (c)AMP (0.1 mM) inhibited endogenous ADP-ribosylation by approximately 35% but had no effect at lower concentrations. 0.5 mM isobutylmethylxanthine inhibited this reaction by approximately 60%. We suggest that TSH enhances thyroid cell ADP-ribosylation by a mechanism independent of cAMP as a second messenger, and that ADP-ribosylation plays a role in the expression of TSH.

Adenosine Diphosphate Ribose↗
PubMed1981

Insulin receptor down-regulation, prevention at a post-receptor site.

Nicotinamide (50mM) prevented insulin-mediated down-regulation of insulin receptors in IM-9 lymphoblastoid cells. Half-maximum effectiveness was between 10 and 33mM. Nicotinamide did not influence insulin binding to the cells, cell viability, insulin degradation or protein synthesis. A variety of inhibitors of ADP-ribosylation reactions besides nicotinamide, most of them pyridine analogues, similarly prevented insulin-induced receptor loss. Spermine decreased the number of insulin receptors in IM-9 cells, but this effect was not inhibited by nicotinamide.

Cells, Cultured↗
PubMed1981

Studies on the bioactivity of radioiodinated highly purified bovine thyrotropin: analytical polyacrylamide gel electrophoresis.

Highly purified bovine TSH (stored in solution at -70 C) was radioiodinated by the stoichiometric chloroamine-T method. The iodinated material ws subjected to analytical polyacrylamide disc gel electrophoresis. TSH was eluted from gel slices (1 mm width) and was analyzed for radioactivity and bioactivity. The latter was determined using the cultured thyroid cell cAMP response assay. Radioactivity in the TSH preparation migrated separately from bioactivity, but concordant with the protein bands observed in gels run in parallel. Further studies performed on bovine TSH purified in our laboratory, as well as on a different TSH preparation of exceptionally high potency (both stored as lyophilized powder) revealed a different pattern, with TSH bioactivity and radioactivity eluting concurrently. Iodination of TSH did not alter its electrophoretic migration on disc gel electrophoresis. In all preparations polymorphism of TSH bioactivity was observed, with at least four separate protein bands containing TSH bioactivity being present in our preparation. The relationship between the degree of iodination and retention of TSH bioactivity was examined. Incorporation of 125I into TSH was greatly different at two different concentrations of chloramine-T. Despite this, however, the progressive loss of TSH bioactivity was similar at both concentrations, indicating that incorporation of iodine into the TSH molecule is not itself responsible for the decrease in bioactivity. These studies indicate variability among different TSH preparations in terms of their retention of bioactivity. Significant loss of TSH bioactivity appears to occur during storage in solution. The damage to the biological activity of TSH during the iodination procedure is more likely related to the oxidation process than to the incorporation of iodine.

Adenoma↗
PubMed1981

Thyroid-stimulating immunoglobulin bioassay using cultured human thyroid cells.

Modifications are described in the cultured thyroid cell cAMP assay for TSH which make it suitable for the measurement of thyroid-stimulating immunoglobulins. Comparison was made between this assay and two others measuring cAMP responsiveness in human thyroid tissue, namely the thyroid slice and thyroid plasma membrane adenylate cyclase assays, all performed with the same tissue sample. Of immunoglobulin G (IgG) samples from 7 unselected patients with untreated hyperthyroidism associated with Graves' disease, 5 produced significant stimulation of cAMP content in cultured thyroid cells when compared to pooled normal IgG. None of these 7 produced a statistically significant increase in thyroid slice cAMP content when assayed in triplicate, the same replicate number used in the cultured thyroid cell assay. Similarly, none of the same Graves' IgG samples produced significant stimulation (vs. control IgG) in the membrane adenylate cyclase assay, in which sensitivity to TSH stimulation was very poor. With a scaled-down modification of the assay using microtiter wells and acetylation to enhance detection of cAMP in the RIA, significant TSI activity was observed in 15 of 18 (83%) IgG samples from patients with untreated Graves' disease. The data indicate the excellent sensitivity and precision of the thyroid cell cAMP assay, as well as its convenience.

Biological Assay↗
PubMed1980

Studies on the pathophysiological role of thyroidal prostaglandin E (PGE) in Graves' disease.

A potential role for prostaglandin E (PGE) of thyroid origin in the pathogenesis of the hyperthyroidism of Graves' disease was investigated in vivo. The venous-arterio prostaglandin E (PGE) concentration gradient across the thyroid was measured in 5 patients undergoing subtotal thyroidectomy for Graves' disease. This gradient (161 +/- 14 pg/ml; mean /+- SE) was significantly greater than that found in 11 patients undergoing surgery for hyperparathyroidism and thyroid nodules (64 +/- 20 pg/ml; P < 0.01). This suggests that there is a net increase in PGE output by the thyroid gland in Graves' disease, but the thyroid cell-type responsible for this increased PGE output is unknown. In contrast to previous reports, thyrotropin (TSH) did not stimulate thyroid cell PGE generation in vitro, providing evidence against a role for TSH in this phenomenon. Administration of maximal doses of indomethacin to two thyrotoxic patients did not significantly alter peripheral thyroid hormone concentrations. These data suggest that thyroidal PGE has a function other than to stimulate thyroid hormone secretion in Graves' disease.

Adult↗
PubMed1980

[Colonic angiodysplasia: report of a case and considerations].

An important etiology of gastrointestinal disease hemorrhage is the angiodisplasic in the last decades the recognition of this pathology has advanced due to the endoscopic and arteriographic techniques. Higher frequency is observed in patients older than 60 years old attributing its etiology to degenerative changes being associated between 20 and 25% with aortic stenosis. Expectant or surgical therapeutics depend on the importance of the hemorrhage and the general state of the patient, the patient that motivated this review presented previous low gastrointestinal hemorrhages. The use of selective arteriography on the last internation allowed us to make the diagnosis of colonic angio displasia.

Angiography↗
PubMed1979

Nerve lipid abnormalities in human diabetic neuropathy: a correlative study.

To study endoneurial lipid composition in human diabetic neuropathy, we biopsied sural nerves from 3 middleaged men with adult-onset diabetes mellitus. Magnitude of electrophysiological abnormalities and myelinated fiber loss paralleled the clinical severity of neuropathy in all cases. Cholesterol ester concentration was elevated to about 800% of normal in diabetic nerves. Reduction in total endoneurial lipid concentration correlated best with decrease in myelin volume as calculated from measured fiber diameters. Cholesterol, cerebroside, and most phospholipids were reduced in keeping with the severity of fiber loss in each nerve. The phosphatidylinositol-phosphatidylserine fraction was most reduced in the least affected nerves. Cerebroside nonhydroxy fatty acids in diabetic nerves were of shorter chain length and more saturated than normal. It is not yet clear whether the abnormalities of phosphatidylinositol-phosphatidylserine and cerebroside fatty acids are of pathogenetic importance or whether these changes may be the nonspecific consequence of axonal degeneration.

Adult↗
PubMed1979

Modulation by thymus-derived (T) cells of thyroid cell-stimulated prostaglandin E release by human peripheral blood mononuclear cells.

Cultures of plastic-adherent, human peripheral blood mononuclear cells generated prostaglandin E (PGE). Culture of the adherent cells (predominantly monocytes) with human thyroid cells enhanced PGE accumulation in the medium, although to a lesser degree than occurs with unseparated blood mononuclear cells. Recombination of the adherent cells with monocyte-depleted, nonadherent cells restored both basal and thyroid cell-stimulated PGE generation to the levels seen with unseparated cells. Thymus-derived (T) cells, obtained by rosetting with sheep erythrocytes, similarly enhanced both the adherent cell basal PGE production as well as the increased PGE accumulation that occurs in the presence of thyroid cells (50-120% augmentation by the T cells). Significant augmentation of thyroid cell-stimulated PGE release by 10(5) adherent cells occurred with the addition of as few as 5 x 10(4) T cells. Culture medium transfer experiments and separation of cell types during culture by a semipermeable membrane provided evidence against the possibility that the adherent cells were releasing a factor that stimulated T-cell PGE generation or that T cells were releasing a factor that enhanced adherent cell PGE generation. The results suggest instead that this T-cell effect requires direct contact with the adherent cells. These data demonstrate the importance of human T cells in the release by adherent cells of PGE, a mediator of suppressor function by some immune cells.

Adult↗