Cumulative Inhibitory Effect Research Articles

Studies on the bradycardia and periodic rhythm caused by veratramine in the sinoatrial node of the guinea pig

In spontaneously beating, isolated guinea pig sinus-atria, veratramine (2.44 μM) slowed the rate of spontaneous depolarization of sinoatrial node cells throughout diastole, markedly slowed the frequency, and often (especially in the presence of high extracellular Ca 2+) induced a periodic rhythm. This rhythm consisted of periods of complete inactivity (inactive phases) alternating with periods of apparently normal beating (active phases), with a rising and falling (parabolic) frequency pattern like that of neuronal burst firing. Slight mechanical deformation of the sinoatrial node markedly attenuated the effects of veratramine, and periodic rhythm could not be produced when the sinoatrial node was pinned down for immobilization. During the active phase of periodic rhythm, the rate of spontaneous diastolic depolarization (pacemaker potential) in pacemaker cells rose and fell with the frequency, while contrariwise, the maximum rate of depolarization fell and then rose. The last beat in the active phase was followed by a small transient afterdepolarization, which had the appearance of an abortive pacemaker potential that failed to reach threshold for triggering an action potential. The effects of various programs of electrical stimulation and pacing indicated that activity of the sinoatrial node, whether spontaneous or driven, has two effects on the amplitude of afterdepolarization, a short-lasting cumulative facilitory effect and a long-lasting cumulative inhibitory effect. Veratramine periodic rhythm arises from the interplay of these two effects, with abrupt cessation of beating whenever the afterdepolarization amplitude falls below the threshold for triggering an action potential. It is suggested that the inhibitory effect may be due to inactivation of the slow inward current and the facilitory effect may be due to one or more of the depolarizing currents activated by intracellular Ca 2+.

TNP-470 (a fungus-derived inhibitor of angiogenesis) reduces proliferation of cultured fibroblasts isolated from primary pterygia: a possible drug therapy for pterygia

PURPOSE. To study drug therapy for pterygium, especially the effect of a fumagillin analog, TNP-470, a potent anti-angiogenic compound, on the growth of cultured fibroblasts obtained from primary pterygia and normal human conjunctiva. METHODS. Cultured pterygium fibroblasts (PF) were exposed to different concentrations of TNP-470 every other day for 7 days (Treatment A) and to a single dose before 4 days of culture (Treatment B). Human normal conjunctival fibroblasts (HCF) were treated with TNP-470 every other day for 7 days. The cells were observed daily by phase contrast microscopy. Cell proliferation was assessed by counting cells with a hemocytometer. Trypan blue uptake was used to determine cell viability at harvest. RESULTS. TNP-470 induced a significant inhibition of PF and HCF proliferation in a dose-dependent manner (P <. 0001). At the lowest dose of TNP-470 (100 pg/ml), the cumulative inhibitory effect of TNP-470 was more potent than the sustained inhibitory effect observed by treatment B in one high dose. Nevertheless, the cytotoxic effect was dose-dependent and more marked after treatment A than after treatment B. After washing out of the drug, partial reversibility was observed at doses lower than 5 mg/ml with a significant increase of viability. HCF were less sensitive to TNP-470 and doses less than 5 mg/ml were not cytotoxic. CONCLUSION. TNP-470 appears to have a marked inhibitory effect on PF proliferation, and it may be of considerable value in the prevention of pterygium growth and recurrence.

Modulation of adrenal cell functions by cadmium salts. 5. Cadmium acetate and sulfate effects on basal and ACTH-stimulated steroidogenesis.

In vitro and in vivo cadmium toxicity studies focus almost exclusively on CdCl2 effects. Only a few studies have used adrenocortical cells and tissue to determine cadmium salt effects during stress of adrenocorticotropin stimulation. Because several biologically relevant water-soluble cadmium salts exist, this study extended work with CdCl2 to evaluate the acute adrenocortical cell steroid secretory responses to non-lethal cadmium acetate (CdAc2) and CdSO4 concentrations. Control or ACTH-stimulated cultured Y-1 mouse adrenal tumor cells (ATCC) which secrete 20alpha-dihydroprogesterone (20-DHP) were incubated for 0.5 h in serum-free medium (FMEM) with or without 0.5, 1.0, 5.0, 10.0, 50.0, 100.0, 500.0 and 1000.0 microg CdAc2 or CdSO4/ml FMEM (1.9, 3.8, 19.0, 38.0, 190.0, 380.0 and 1900.0 micromol/L, respectively). For each salt, cell viability was measured at the end of the incubation using live cell trypan blue exclusion. In addition, cumulative CdAc2 effects during 4 h incubations and effect reversibility were determined for control and stimulated cells. After each experimental incubation, the 20-DHP secreted into the medium was determined by radioimmunoassay. Over 80% of all control or ACTH-stimulated cells were viable after incubation in the presence or absence of various CdAc2 or CdSO4 concentrations. Cadmium acetate and sulfate inhibited basal and ACTH-stimulated steroid secretion in a dose-dependent manner. For basal steroid secretion the CdAc2 concentration that first significantly inhibited was 0.5 microg/ml medium (1.9 micromol/L); stimulated secretion was significantly inhibited beginning at 5.0 microg/ml (19.0 micromol/L) and the concentration reducing stimulated 20-DHP secretion by 50% (IC50) was 5.6 microg/ml (21.3 micromol/L). Similarly, the first CdSO4 concentration to significantly inhibit basal and ACTH-stimulated steroid secretion was 10.0 microg/ml medium (39.0 micromol/L); the IC50 was 7.8 microg/ml (29.8 micromol/L). Except that basally secreting Cd2+-treated cells almost doubled 20-DHP secretion after Cd2+ removal and subsequent incubation with ACTH, all basal and ACTH-stimulated steroid secretion was irreversibly inhibited by every CdAc2 concentration. All CdAc2 concentrations initiated and maintained cumulative inhibitory effects on basal and ACTH-stimulated steroid secretion over a 4 h period. Reversibility and cumulative CdSO4 treatment studies were not conducted. Based on the results from the present studies, both CdAc2 and CdSO4 appeared to incrementally inhibit control and ACTH-stimulated steroidogenesis without affecting cell viability and to be more potent inhibitors of adrenocortical cell steroid secretion than CdCl2. Finally, CdAc2 effects on control and stimulated cells were cumulative and irreversible.

Isoforms of Glutamine Synthetase in the Marine Coccolithophorid Emiliania huxleyi (Prymnesiophyceae)

Two isoenzymes of glutamine synthetase (EC 6.3.1.2), GS1 and GS2, have been purified from cells of Emiliania huxleyi using Cibacron blue dye ligand chromatography and gel filtration, separated by ion-exchange chromatography on Mono-Q and partly characterized. Each enzyme is a homohexamer with a molecular mass of 402 kDa for GS1 and 501 kDa for GS2. The molecular mass of the subunits of GS1 and GS2 was estimated to be 61 and 78 kDa, respectively. As in higher plants, GS1 is slightly more thermostable than GS2 and much less stimulated by thiols than GS2. For these reasons, GS1 was designated as the cytosolic enzyme and GS2 as the chloroplastic one. Although the Kms for NH2OH are about the same, GS2 possesses a much higher affinity for glutamine than GS1. As in bacteria, ATP appears to play an important role in the allosteric regulation of GS2. l-Ala and CTP are potent inhibitors of GS1 activity. CTP, carbamoyl-phosphate and l-Ala exert a cumulative inhibitory effect on GS1 activity. GS2 is also inhibited to some extent by l-Ala and l-His. NH2-terminal sequence analysis of GS2 did not show any homology with bacteria, cyanobacteria or higher plants.

Sequential activation of the triple excitatory transmission to the circular muscle of guinea-pig colon

The aim of this study was to resolve the temporal relationships of the triple excitation of the circular muscle of guinea-pig colon that occurs in response to activation of the intrinsic excitatory nerves by using atropine and tachykinin NK 1 and NK 2 receptor selective antagonists to define the relative contribution of the transmitters involved. In organ bath experiments, performed in the presence of blockers of inhibitory innervation, a train of electrical pulses at 5 Hz for 300 s produced a sustained contraction of the circular muscle of guinea-pig colon: the sequential addition of atropine (1 μM), of the tachykinin NK 1 receptor antagonist, SR 140333 (0.3 μM) and of the tachykinin NK 2 receptor antagonist, MEN 11420 (1 μM) produced a cumulative inhibitory effect and progressively delayed the onset of the contractile response to nerve stimulation. In the presence of peptidase inhibitors, atropine was less effective in inhibiting the contractile response for prolonged periods of stimulation: however, the pattern of inhibition of the evoked response produced by the sequential addition of blocker drugs was not substantially affected. The selective tachykinin NK 3 receptor agonist, senktide, produced a concentration-dependent contraction of guinea-pig colon. The sequential addition of atropine (1 μM), SR 140333 (0.3 μM) and MEN 11420 (1 μM) reproduced the effect of the same drugs on the response to electrical nerve stimulation. The peptide blocker of N-type voltage-dependent calcium channels, ω-conotoxin (0.1 μM) produced a partial inhibitory effect of the response to senktide. The ω-conotoxin-resistant response to 1 μM senktide was inhibited and delayed by the progressive application of atropine, SR 140333 and MEN 11420, similar to the effect observed in the absence of ω-conotoxin. In sucrose gap, single-pulse electrical field stimulation produced a fast excitatory junction potential which was largely (>90%) inhibited by atropine; application of a low concentration of the potassium channel blocker, 4-aminopyridine (30 μM), markedly enhanced the atropine-resistant excitatory junction potential which was abolished by the NK 1 receptor antagonist, GR 82334. We conclude that, during prolonged electrical or chemical stimulation of excitatory motorneurons, there is a sequential, time-dependent activation of the three excitatory mechanisms in the circular muscle of guinea-pig colon: the pattern of activation is relatively independent of the intensity of stimulation and/or the mechanisms of secretion of released transmitters. Postjunctional factors predominate in determining the relative contribution of the three transmitters, acetylcholine, substance P and neurokinin A, in producing excitation of the circular muscle.

Interference of interleukin-10 with human immunodeficiency virus type 1 replication in primary monocyte-derived macrophages.

Previously we demonstrated an inhibitory effect of interleukin-4 (IL-4) on establishment of human immunodeficiency virus type 1 (HIV-1) infection in primary macrophages. The reported similarities between the biological effects of IL-4 and IL-10 prompted us to study the effect of IL-10 on HIV-1 replication. Treatment of primary macrophages with IL-10 resulted in inhibition of HIV-1 infection. This inhibitory effect was specific for macrophages, since IL-10 did not interfere with HIV-1 replication in primary T cells. Semiquantitative PCR analysis excluded an inhibitory effect of IL-10 on virus entry and reverse transcription. Effects of IL-10 on HIV-1 long terminal repeat-driven chloramphenicol acetyltransferase activity also could not be demonstrated in a transient expression system in primary derived macrophages. In agreement with this, Northern (RNA) blot analysis demonstrated equal amounts of viral RNA species irrespective of IL-10 treatment, also excluding an inhibitory effect on elongation of virus transcription. Monocyte-derived macrophages (MDM) treated with IL-10 after HIV-1 inoculation showed accumulation of apparently mature p24 protein suggestive of an inhibitory effect at the level of virus assembly. IL-10 treatment of MDM prior to HIV-1 inoculation did not result in accumulation of p24 protein. Immunoblot analysis indeed showed the absence of mature p24 and gp120 but accumulation of the Pr53 gag-encoded protein in HIV-1-inoculated, IL-10-pretreated MDM, suggesting an inhibitory effect at the level of protein processing. A combination of IL-4 and IL-10 resulted in a cumulative inhibitory effect on HIV-1 replication in MDM. The recent observation that in the course of HIV-1 infection a shift occurs in the production of IL-2/gamma interferon toward enhanced IL-4 and IL-10 production and the reported shift from preferential macrophage-tropic towards preferential T-cell-tropic HIV-1 variants with progression of disease suggest that cytokines have an important role in the in vivo regulation of HIV-1 tropism.

Ammonium chloride inhibits pyruvate oxidation in rat liver mitochondria: a possible cause of fatty liver in Reye's syndrome and urea cycle defects.

1. Earlier studies with liver slices showed that inhibition by NH4+ of the oxidation of palmitate to CO2 was greater than total oxidation, whereas salicylate exerted a stronger inhibitory effect on the latter. We have now investigated the effects of NH4Cl and salicylate on ADP-induced O2 consumption by mitochondria (State 3 rate) respiring on pyruvate, and oxidation of [1-14C]- and [2-14C]-pyruvate to 14CO2. 2. The rate of State 3 respiration was inhibited and plateaued at 45% with 10 mmol/l NH4Cl. 3. Oxidation of [1-14C]pyruvate was not significantly affected by either NH4Cl or salicylate. Oxidation of [2-14C]pyruvate was strongly inhibited and plateaued at 70% with 1 mmol/l NH4Cl (IC50 = 0.125 mmol/l). ADP (1 mmol/l) increased the rate of decarboxylation of [2-14C]pyruvate but the extent of NH4Cl inhibition was not affected. Salicylate had a slight activating effect in the absence or presence of NH4Cl. 4. These results indicate that NH4Cl inhibits the oxidative metabolism of acetyl-CoA in the tricarboxylic acid cycle. Therefore, inhibition of fatty acid oxidation to acetyl-CoA as well as its further oxidative metabolism occurring under hyperammonaemia (> 0.1 mmol-1.49 mmol/l in Reye's syndrome patients) may be one of the causes of fatty acidaemia. 5. The cumulative inhibitory effects of NH4+ and fatty acyl derivatives on mitochondrial oxidative metabolism and production of ATP, as well as the uncoupling effects of salicylate, may contribute to some of the pathophysiology observed in patients with Reye's syndrome, and enzyme defects of the urea cycle.

Iloprost and tissue-type plasminogen activator differently affect platelet aggregation in platelet-rich plasma and in whole blood

Platelet aggregation in platelet-rich plasma (PRP) is more sensitive to agonists and more resistant to antagonists than that in whole blood. In this study, we show that the presence of neutrophils in whole blood accounts at least in part for diminished platelet aggregation in whole blood. The platelet-inhibitory effect of neutrophils relates to the release of nitric oxide and not to elastase or adenosine. Furthermore, two unrelated platelet inhibitors, iloprost and tissue-type plasminogen inhibitor, decrease platelet aggregation to a greater extent in whole blood than in PRP. However, these agents exert cumulative or synergistic inhibitory effects with neutrophils on platelet aggregation in PRP. Thus, the inhibition of platelet aggregation in vivo may relate to the interaction between neutrophils and platelet-inhibitory agents.

OVERVIEW: Modulation by Sex Steroids and [d-TRP6, Des-Gly-NH210]Luteinizing Hormone (LH)-Releasing Hormone Ethylamide of α-Subunit and LHβ Messenger Ribonucleic Acid Levels in the Rat Anterior Pituitary Gland

LHRH and sex steroids play a major and direct regulatory role in the secretion of LH by the anterior pituitary gland. The aim of the present study was to investigate the interactions between sex steroids, more especially the potentiating effect of progesterone (P) in the presence or absence of a low dose of 17 beta-estradiol (E2) and/or dihydrotestosterone (D) on mRNA levels encoding the alpha- and beta-subunits of LH in both female and male rats. We also studied the effect of 2-week treatment with the LHRH agonist [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide on the same parameters. After treatment with the LHRH agonist (5 micrograms daily), the accumulation of mRNA encoding the alpha-subunit was stimulated by approximately 3-fold while the LH beta mRNA concentration remained unchanged. Ovariectomy performed 14 days earlier, increased pituitary alpha and LH beta mRNA levels by 3.7- and 8.8-fold, respectively, while orchiectomy performed 14 days earlier increased alpha and LH beta mRNA levels by 6- and 6.5-fold, respectively. The present data demonstrate that although P alone exerts no effect on alpha and LH beta mRNA levels in castrated animals, treatment with P markedly potentiates the inhibitory effect of E2 on both mRNA levels in female as well as male rats. In addition, P potentiates the inhibitory effect of D on LH beta mRNA levels in castrated female rats. Furthermore, the present study illustrates the importance of the cumulative inhibitory effects of relatively low doses of E2 and D on mRNAs encoding both LH subunits. Moreover, the present observation of a differential modulation of alpha-subunit and LH beta mRNA levels after chronic treatment with an LHRH agonist offers an explanation for the high plasma levels of free alpha-subunit found in patients treated with LHRH agonists.

DAYLENGTH AND LIGHT RESPONSES IN GROWTH AND FERTILITY OF GLOSSOPHORA KUNTHII (PHAEOPHYTA, DICTYOTALES) FROM PACIFIC SOUTH AMERICA1

ABSTRACTExcised ligulae of Glossophora kunthii (C. Ag.) J. Ag. were cultured in photoperiods of 4–24 h and photon fluence rates of 10–75 μmol.m−2.s−1. Daylength interacted with irradiance on the growth of the ligulae. Maximal growth of primary ligulae occurred in long‐day regimens with high irradiances suggesting an effect of irradiance on photosynthesis and growth. In contrast, growth of secondary ligulae was greatest in short‐day regimes. Differences were significant at the highest irradiance tested. Differentiation of tetrasporangia on the ligulae is a short‐day photoperiodic response. Daylengths of 8.5 h or less induced a sharp increase in numbers of fertile ligulae and tetrasporangia attaining maturity. Interruptions of the dark period decreased the development of tetrasporangia; the number of interruptions had a cumulative inhibitory effect. Differentiation of reproductive structures was influenced by interactions of photoperiod and irradiance. Maximum numbers of tetrasporangia were formed at short‐day regimes and low irradiances; differentiation was completely inhibited at long‐day conditions and high irradiance.

The effect of wood‐derived inhibitors on 2, 3‐butanediol production by Klebsiella pneumoniae

Four potential inhibitors, hydroxymethylfurfural, furfural, syringaldehyde and vanillin, were assayed over a range of concentrations and times to simulate the amounts that might be expected to accumulate when the hydrolyzed water-soluble fraction from steam-treated aspenwood was added in a fed-batch mode to K. pneumoniae. Combinations of the individual materials resulted in a cumulative inhibitory effect. Prolonged incubation could alleviate some of the inhibition.

Effects of low doses of aspirin, 10 mg and 30 mg daily, on bleeding time, thromboxane production and 6-keto-PGF1α excretion in healthy subjects

To compare the long term effects of two low doses of aspirin taken daily, we performed a placebo-controlled cross-over study in 19 normal subjects. Aspirin 10 mg daily for 3 weeks caused a significant inhibition by 61 ± 12 percent of platelet thromboxane B 2 generation but had no effect on the Simplate bleeding time. Aspirin 30 mg daily for 3 weeks reduced thromboxane B 2 production by 94 ± 5 percent and caused a significant prolongation of the bleeding time, 1.6 times the control value. No cumulative inhibitory effects were observed after the first week of treatment. Both doses did not effect the urinary excretion of 6-keto-PGFla.

Cumulative inhibitory effect of low-dose aspirin on vascular prostacyclin and platelet thromboxane production in patients with atherosclerosis.

The relationship between the antithrombotic and antiplatelet effects of aspirin is complex, since aspirin influences other systems that protect against thrombosis as well as inhibiting platelet function. We investigated possible cumulative effects of low-dose aspirin on vascular production of prostacyclin in patients with documented atherosclerotic cardiovascular disease. Candidates for coronary artery vein graft bypass ingested 20 mg of aspirin daily during the week before surgery, and platelet aggregation, platelet formation of thromboxane A2 (TXA2), aortic and saphenous vein production of prostacyclin (PGI2), and hemostatic status were measured at the time of the bypass surgery. Low-dose aspirin markedly inhibited platelet aggregation responses and reduced TXA2 generation by greater than 90%, effects similar to those observed with much higher doses of aspirin. Both aortic and saphenous vein production of PGI2 were inhibited by 50% compared with PGI2 produced by vascular tissues of control subjects who received no aspirin preoperatively (51 +/- 10 pg 6-keto-PGF1 alpha/mg aortic wet weight [mean +/- SEM] in aspirin-treated subjects vs 130 +/- 16 pg/mg in control subjects, and 71 +/- 8 pg/mg saphenous vein wet weight vs 131 +/- 17 pg/mg). Blood loss at surgery was not significantly increased by preoperative low-dose aspirin as measured by chest tube drainage (754 +/- 229 ml in aspirin-treated subjects vs 645 +/- 271 ml in control subjects), hematocrit nadir (31.2 +/- 1.9% vs 31.8 +/- 1.7%), or transfusions (2.2 +/- 1.3 units of red blood cells vs 2.2 +/- 1.7 units).(ABSTRACT TRUNCATED AT 250 WORDS)

Low-dose aspirin inhibits platelet and venous cyclo-oxygenase in man

In a group of normal subjects we have compared rates of recovery of venous prostacyclin (PGI 2) and platelet thromboxane B 2 (TXB 2) production after a single 300 mg dose of aspirin. Marked inhibition of both venous PGI 2 synthesis and platelet TXB 2 synthesis persisted for the 72 hours duration of the study. We also examined the effect of four daily doses of 40 mg aspirin on platelet and vessel wall prostaglandin biosynthesis. This produced a cumulative inhibitory effect on TXB 2 production with 98.6 per cent mean inhibition at 72 hours. At this time 81 – 100 per cent inhibition of PGI 2 was demonstrated in the four subjects studied. We conclude that the cyclo-oxygenase enzyme in human vein is sensitive to inhibition by very low doses of aspirin. No evidence was found to substantiate the view that rapid recovery of vessel wall cyclo-oxygenase activity occurs after inhibition by a single dose of aspirin.

Effect of water pollutants and other chemicals upon the activity of lipase in vitro.

Lipase preparations were treated in vitro with 100 chemicals of various classes, many of which are environmental pollutants, to determine their effect upon enzyme activity. The greatest inhibition was caused by mercuric ion and certain heavy metal cations; almost as inhibiting were pentachlorophenol, dicofol, 2,4,5-trichlorophenol, and DDT. Less inhibition was found with other inorganic salts, organo-metals, other organic chemicals, and some pesticides. Apart from dichromate ion, the anions studied had a low to negligible effect on lipase. A mixture of 10 inorganic salts had an approximately cumulative inhibitory effect on enzyme activity. None of the chemicals studied caused a measurable activation of the enzyme.

Inhibition of Specific Immune Responses by Feeding Protein Antigens

Abstract Single and multiple intragastric feedings of ovalbumin (OVA) to high-responder BDF1 mice resulted in virtually complete unresponsiveness to later parenteral immunization with OVA in Al(OH)3 adjuvant, as indicated by antibody titers in Farr assays and in passive cutaneous anaphylaxis (PCA) assays for IgE antibodies. Repeated feedings of partially tolerizing doses of antigen had a cumulative inhibitory effect on subsequent responsiveness. Slight increases in primary antigen binding were detected in the serum of antigen-fed mice not given parenteral immunization, although rates of clearance of radiolabeled OVA from the blood were similar in normal and tolerant animals. Serum recovered from tolerant mice 7 or 14 days after feeding did not inhibit antibody responses of normal recipients. Responsiveness of normal or OVA-primed syngeneic spleen cells was substantially reduced upon transfer into recipients that were previously fed OVA, when compared with transfer into saline-fed recipients. The differences in responsiveness of lymphocytes transferred into OVA- and saline-fed mice were completely eliminated by irradiation (850 R) of the recipient animals either 7 or 20 days after feeding and immediately before the transfer. The results indicated that the state of tolerance after ingestion of OVA is actively maintained, but did not support the hypothesized mediation of this tolerance by orally induced antibodies or serum factors that have been associated with unresponsiveness to ingested antigens in similar experimental systems.

Effect of Potassium Sorbate on the Microbiological Quality of Butter

Butter samples treated with potassium sorbate and sodium chloride were analyzed weekly for bacteriological qualities after storage at different temperatures. Addition of 0.1% potassium sorbate and incorporation of 2% sodium chloride plus 0.1 percent potassium sorbate resulted in inhibition of mold growth in all the samples at the end of 4 weeks at 18 C and 5 C. However the effect of potassium sorbate alone was less pronounced, irrespective of storage temperature. As regards coliform count in control butter, it increased rapidly at 22 C, but decreased when butter was stored at 5 C or – 18 C. Addition of potassium sorbate to butter samples stored at 18 C reduced the coliform count to zero after 4 weeks. while butter with added potassium sorbate and sodium chloride showed a zero count after 1 week, indicating a cumulative inhibitory effect.

The cumulative inhibitory effect of repetitively flashed stimuli on the recovery process of the human visual evoked potential to a test stimulus

Cumulative inhibitory effects produced by visual response to flashed conditioning stimuli were measured by means of the amplitude reduction of the visual evoked potential (VEP) to a test stimulus. Four kinds of conditioning stimuli were used: a single conditioning stimulus and 3 repetitive conditioning stimuli with interstimulus intervals (ISIs) of 100, 200 and 400 msec, respectively. The VEP amplitude for the test stimulus was reduced most when the stimulus was paired with the single conditioning stimulus. It still remained small when the test stimulus was paired with the repetitive conditioning stimulus of 400 msec ISI, increased significantly when the ISI was shortened from 400 to 200 msec. Explanations of the VEP behaviors in terms of stimulus relevance, task difficulty and the recovery rate of the cortical excitability were discussed.

Effects of amino acids, adenine nucleotides and inorganic pyrophosphate on glutamine synthetase from Anabaena cylindrica

Glutamine synthetase ( l-glutamate: ammonia ligase (ADP-forming), EC 6.3.1.2) from Anabaena cylindrica was inhibited by alanine, glycine,serine and aspartate. The effects of alanine and serine were uncompetitive with respect to glutamate, while those of glycine and aspartate were non-competitive and mixed type respectively. Different pairs of amino acids and their various combinations caused a cumulative inhibition of the enzyme activity. Glutamine synthetase was also inhibited by ADP and AMP and both nucleotides affected the enzyme competitively with respect to ATP and non-competitively for glutamate. Inorganic pyrophosphate, between 2 and 3 mM, produced a very pronounced inhibition of enzyme activity. The inhibition by PP i was uncompetitive for ATP. Various combinations of the adenine nucleotides, PP i and P i exerted a cumulative inhibitory effect on the enzyme activity, as did the amino acids, in different combinations with either adenine nucleotides, PP i or P i. The effects of the adenine nucleotides and the amino acids were more pronounced at higher concentrations of ammonia. Except for serine similar responses of these effectors were obtained with increasing concentrations of Mg 2+. It is proposed that changes in the free concentrations of Mg 2+ are important in energy-dependent regulation of the enzyme activity in this alga.

Proceedings: Bi-weekly chlorambucil treatment of chronic lymphocytic leukemia.

Because the lymphocytes of chronic lymphocytic leukemia (CLL) are known to proliferate slowly, it was postulated that intermittent therapy might have a cumulative inhibitory effect on tumor cells while permitting normal cells to recuperate between doses. Sixty-two evaluable patients with CLL were treated with chlorambucil given orally as a single pulse every 2 weeks. The initial dose was 0.4 mg/kg; subsequent doses were increased by 0.1 mg/kg until toxicity or disease control was achieved. Responses were obtained in 6 of 8 (75%) previously untreated patients with indolent disease, in 18 of 31 (61%) previously untreated patients with active disease, in 7 of 14 (50%) previously treated patients not shown to be resistant to alkylating agents, and in 2 of 9 (22%) patients resistant to prolonged daily chlorambucil therapy. The over-all effectiveness in patients with CLL not previously resistant to chlorambucil was 31 of 53 (58%), with five complete remissions (9%). Hematologic toxicity was usually mild and never life-threatening. Gastrointestinal toxicity, which occurred in 23 of 62 patients, was usually mild and easily controlled with anti-emetics. It is concluded that bi-weekly oral administration of chlorambucil is effective therapy for CLL with response rates similar to daily continuous chlorambucil. Hematologic toxicity is considerably less than with daily treatment.