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Biomedical subjects

M Steiner

Publications and source records attributed to M Steiner.

At least 379 records · Page 21Linked to original sources
PubMed1984

Modification of platelet function and arachidonic acid metabolism by bioflavonoids. Structure-activity relations.

The mechanism of the antiaggregating activity of flavonoids was studied in vitro. The activity of fifteen different compounds was tested on platelet aggregation and arachidonic acid metabolism. The effect of flavonoids on platelet adenosine 3',5'-cyclic monophosphate (cyclic AMP) levels under basal conditions, as well as after stimulation by prostacyclin (PGI2), was also measured. The glycons of flavonoids in general and the flavanone derivatives that we tested did not affect platelet function. On the other hand, flavone, chrysin , apigenin and phloretin inhibited platelet aggregation by depressing the cyclooxygenase pathway. In addition, flavone, chrysin and apigenin reduced the platelet cyclic AMP response to PGI2. This effect was probably mediated by an inhibition of adenylate cyclase. Myricetin and quercetin, however, increased the PGI2-stimulated rise of platelet cyclic AMP. Both of these flavonoids inhibited primarily lipoxygenase activity. Modification of platelet cyclic AMP metabolism through inhibition of phosphodiesterase activity was found to be the probable mechanism of their antiaggregating effect.

Arachidonic Acid↗
PubMed1984

Halide binding by the purified halorhodopsin chromoprotein. I. Effects on the chromophore.

The halorhodopsin chromoprotein, a retinal-protein complex with an apparent molecular mass of 20 kilo-daltons, exhibits all of the halide-dependent effects found for the chromophore of functional halorhodopsin in cell envelope vesicles. With increasing halide concentration (a) an alkali-dependent 580/410 nm chromophore equilibrium (attributed to reversible deprotonation of the retinal Schiff's base) is shifted toward the 580-nm chromophore and (b) the flash-induced photocycle proceeds increasingly via P520, rather than via P660. The halide-binding site(s) responsible for these effects must reside, therefore, in the chromoprotein. Chloride and bromide are about equivalent, but iodide is much less effective in these effects and in being transported. Several other anions, i.e. thiocyanate, nitrate, phosphate, and acetate, affect the absorption maximum of the chromophore but do not allow the production of P520 upon flash illumination and are not transported. However, these ions appear to compete with chloride in the flash experiments. These observations suggest that binding of anions to a relatively nonspecific site affects the protonation state of the Schiff's base in the chromophore. Either this site directly or a more specific site, connected to the first one by a sequential pathway, is involved with the photocycle intermediates and with chloride transport by halorhodopsin.

Anions↗
PubMed1984

Halide binding by the purified halorhodopsin chromoprotein. II. New chloride-binding sites revealed by 35Cl NMR.

Halorhodopsin is a light-driven chloride pump in the cell membrane of Halobacterium halobium. Recently, a polypeptide of apparent Mr = 20,000 has been purified that contains the halorhodopsin chromophore. Here we use 35Cl NMR to show that the purified chromoprotein possesses two previously unknown classes of chloride-binding sites. One class exhibits a low affinity (KD much greater than 1 M) for chloride and bromide. The second class exhibits a higher affinity (KD = 110 +/- 50 mM) for chloride and also binds other anions according to the affinity series I-, SCN- greater than Br-, NO-3 greater than Cl- greater than F-, citrate. Both classes of NMR site remain intact at pH 11, indicating that the essential positive charges are provided by arginine. Also, both classes are unaffected by bleaching, suggesting that the sites are not in the immediate vicinity of the halorhodopsin chromophore. Although the chromoprotein also appears to contain the chloride-transport site (Steiner, M., Oesterhelt, D., Ariki, M., and Lanyi, J. K. (1984) J. Biol. Chem. 259, 2179-2184), this site was not detected by 35Cl NMR, suggesting that the transport site is in the interior of the protein where it is sampled slowly by chloride in the medium. It is proposed that the purified chromoprotein possesses a channel leading from the medium to the transport site and that the channel contains the high affinity NMR site which facilitates the migration of chloride between the medium and the transport site. We have also used 35Cl NMR to study chloride binding to purified monomeric bacteriorhodopsin; however, this protein contains no detectable chloride-binding sites.

Bacteriorhodopsins↗
PubMed1984

Platelet activation studied by fluorescence polarization.

Platelet activation was elevated by changes in the fluorescence anisotropy of the sulfhydryl-reactive fluorescent probe, (5-[2-(iodoacetyl) aminacetyl]aminonaphthalene-1-sulfonic acid. The membrane-permeable fluorophore was shown to bind to a multitude of cytoplasmic and membrane proteins. Platelets were stimulated by addition of thrombin, arachidonic acid or ADP under conditions that did not induce aggregation. A sudden increase in the fluorescence anisotropy, r of moderate degree (25-33%) occurred during the first 60 s after exposure of platelets to the aggregating agents and was sustained during the entire period of observation (15-18 min). Phenylmethylsulfonyl thrombin was unable to produce these changes in fluorescence anisotropy. Preincubation of platelets with colchicine reduced r within 30-60 s after platelets were exposed to thrombin. These findings are interpreted as an indication of a general decrease in the 'motional freedom' of the fluorophores and indirectly their ligand molecules.

Adenosine Diphosphate↗
PubMed1984

Inhibition in vitro of platelet aggregation and arachidonic acid metabolism by flavone.

The effects of flavone on platelet aggregation and arachidonic acid (AA) metabolism were tested in vitro. When incubated at a concentration of 50 microM, flavone completely suppressed platelet aggregation induced by 150 microM AA in thirty-six out of forty-three subjects tested. A lower concentration (10 microM) was effective in about 50% of the donors. Flavone also inhibited the second wave of aggregation induced by epinephrine and ADP. Platelet thromboxane formation, estimated both by radioimmunoassay measurements and by studies of 14C-labeled AA metabolism, was depressed by flavone. Flavone-treated platelets preferentially utilized [14C]AA for the lipoxygenase pathway while cyclo-oxygenase activity was depressed. Adenosine 3':5'-cyclic monophosphate (cAMP) was measured in flavone-treated and control platelets. While their baseline levels were similar, flavone-treated platelets showed a lower stimulation of cAMP induced by prostacyclin (PGI2) than did controls. Phosphodiesterase activity was not affected by flavone as judged from the decay rates of PGI2-stimulated cAMP levels. From these findings we conclude that the antiaggregating activity of flavone is not a consequence of changes in platelet cAMP but is due to inhibition of cyclo-oxygenase.

Arachidonic Acid↗
PubMed1984

Fluorescence anisotropy changes in platelet membranes during activation.

Dynamic changes in platelet membrane components were evaluated by two fluorescent probes, the anion channel blocker 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) and the membrane-impermeant stachyose derivative of pyrenebutyryl hydrazide (SPBH). Fluorescence anisotropy, r, was measured in intact platelets treated with either fluorophore. Activation of platelets by thrombin, arachidonic acid, and ADP under nonaggregating conditions increased the anisotropy values of DIDS within 60-120 s. A slow return to base-line values occurred after 8-10 min. Thrombin produced an initial transient reduction of r during the first 60 s. Its effect was specific as inactivated enzyme did not induce any changes. The latter could also be prevented by omitting Ca2+ from the platelet suspension. Treatment of platelets with SPBH, a fluorophore inserted into the lipid leaflet of membranes, revealed an activation-induced increase of its fluorescence anisotropy during the first 120 s. It was followed by a 6-8 min lasting decline of r when thrombin and ADP were the stimulants. Preexposure of platelets to colchicine did not change significantly the fluorescence anisotropy pattern of either fluorophore, but cytochalasin B inhibited such changes almost completely. The findings are interpreted as demonstrating greater motional freedom in the lipid bilayer but a decrease in this parameter in membrane proteins upon stimulation of platelets.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1984

A psychoendocrine study of premenstrual tension syndrome. A model for endogenous depression?

We studied 42 women with severe Premenstrual Tension Syndrome (PMTS) and compared their clinical features and adrenocortical function with those seen in major depressive disorders. Self-report scales demonstrated that PMTS was very distressing, but the disturbance did not meet the RDC for Major Depressive Disorder -- endogenous subtype. Twenty-four hour urinary free cortisol estimation did not indicate cortisol hypersecretion and abnormal Dexamethasone Suppression Test results occurred much less frequently than is usual in endogenous depression. Adrenocortical function did not differ significantly between follicular and premenstrual phases. PMTS does not appear to be a psychoendocrine model for endogenous depression.

Adult↗
PubMed1984

Plasma prolactin and severe premenstrual tension.

It has been suggested that elevated luteal phase prolactin (PRL) levels may have an important role in causing some of the symptoms of the premenstrual tension syndrome (PMTS). Thirty-seven women suffering from severe premenstrual dysphoria were selected for this study. Single morning and afternoon serum PRL evaluations were performed during the follicular (day 9) and late luteal (day 26) phases of the menstrual cycle. PRL was measured by an established double antibody radioimmunoassay technique. All mean PRL values were within the normal range. Only afternoon mean PRL levels showed a tendency for a premenstrual increase. The significance of this statistical finding is unclear, since one-third of the subjects showed a decrease in premenstrual PRL levels. Twenty-four hour PRL secretory profiles recorded on days 9 and 26 in two women with extremely severe PMTS and in two asymptomatic matched control subjects also failed to show a significant correlation between PRL levels and PMTS. Thirty subjects participated in a treatment trial using bromocriptine. A marked rebound hyperprolactinemia was observed in a subgroup of women nine days after cessation of bromocriptine. This was associated with no detectable effect on mood, behavior, or menstrual regularity. Thus, our data fail to show any specific relationship between PRL and PMTS.

Adult↗
PubMed1984

In vivo study of LDH isoenzyme activities in heart, liver and testis cytosols of gossypol-treated rats.

LDH isoenzyme activities of heart, liver and testis homogenates were measured in rats treated for 15 or 30 days with 30 mg gossypol acetic acid/kg body weight daily, a dose which severely suppressed sperm motility. No differences in LDH activities of the examined organs were found in comparison with control animals. LDH-X, the main LDH isoenzyme in spermatozoa and testicular germ cells from primary spermatocytes onwards was also unaffected. These results contrast with in vitro experiments on human, rabbit, and boar spermatozoa, purified bovine LDH-X and rat testis homogenate which show dose-dependent inhibition of LDH-X after incubation with gossypol. Our results therefore suggest that inhibition of LDH by gossypol is not the primary cause of sperm immotility.

Animals↗
PubMed1984

Circadian hormone secretory profiles in women with severe premenstrual tension syndrome.

The circadian secretory profiles of serum prolactin, growth hormone and cortisol were measured in two women suffering from severe premenstrual tension syndrome and in two asymptomatic control subjects. Subjects and controls were screened and included after a rigorous selection process. Blood samples were obtained every 30 min over a period of 24 h in each woman both on day 9 (follicular phase) and day 26 (luteal phase) of the menstrual cycle. There was no relationship between the hormonal secretory profiles and the premenstrual tension syndrome.

Adult↗
PubMed1984

Ethanol raises prostacyclin in vivo and in vitro.

Moderate doses of ethanol were shown to induce a significant rise in prostacyclin (PGI2) concentration in cultures of endothelial cells derived from umbilical veins. Administration of 32 g of ethanol to six volunteers elevated plasma levels of PGI2 in parallel with those of blood alcohol. Although not specific for ethanol, this alcohol induced the largest change in PGI2. Withdrawal of the stimulant alcohol caused prompt reduction of the elevated prostacyclin to baseline values. The activity of ethanol appears to be due to a direct stimulation of cyclooxygenase. The release of [14C]arachidonic acid from prelabeled endothelial cells was decreased by ethanol. PGE2 production was also enhanced by exposure of endothelial cells to ethanol. The physiologic significance of these alcohol-induced changes in PGI2 levels remains to be established.

Adult↗