Platelet desensitization by arachidonic acid is associated with the suppression of endoperoxide/thromboxane A2 binding to the membrane receptor

The inhibitory mechanism of high levels of exogenously added arachidonic acid on activation of washed human platelets was investigated. While low levels of arachidonic acid (5-10 microM) induced aggregation, ATP secretion and increase in cytoplasmic free Ca2+ concentration (first phase of activation), these platelet responses did not occur significantly at high concentrations (30-50 microM). However, much higher concentrations than 80 microM again elicited these responses (second phase). The first phase of platelet activation was inhibited by cyclooxygenase inhibitor, indomethacin, whereas the second one was independent of such treatment. Thromboxane B2 was produced dose-dependently until reaching a plateau at arachidonic acid concentrations higher than 20 microM, irrespective of the lack of aggregation and secretion at high concentrations. After that the amount of free arachidonic acid which remained unmetabolized in platelets gradually increased. High concentrations of arachidonic acid as well as other polyunsaturated fatty acids caused desensitization of platelets in response to U46619, and also depressed the specific [3H]U46619-binding to the receptor as well as other polyunsaturated fatty acids. The amount free arachidonic acid needed in platelets to suppress [3H]U46619 binding corresponded to that needed to inhibit platelet aggregation. Furthermore, arachidonic acid dose-dependently induced fluidization of lipid phase of platelet membranes as detected by 1,6-diphenyl-1,3,5-hexatriene. These results suggest that the inhibition of platelet response by high levels of arachidonic acid can be attributed to interference with endoperoxide/thromboxane A2 binding to the receptor, probably due to perturbation of the membrane lipid phase due to excess amounts of free arachidonic acid remaining in the membranes.     

Genetic parameters of egg characteristics in Japanese quail

Heritability, phenotypic and genetic correlations of egg characteristics of Japanese quail were investigated to obtain basal information on breeding, strain identification and genetic monitoring. For this study, 3230 eggs produced from 323 female were used. Measurement were taken on egg weight, yolk weight, albumen weight, shell weight, egg shape index, albumen height, specific gravity, shell thickness, shell strength and yolk color. Heritability estimates of egg characteristics were high and ranged from 0.62 to 0.84. Diverse phenotypic and genetic correlations were observed among egg characteristics. These results indicate that individual selection should be the most efficient method of improving egg characteristics and that consideration should be given to the interrelationship of characteristics to accomplish genetic improvement. The possibility exists these assays of egg characteristics can be used for strain identification and genetic monitoring without killing an individual of quail.     

Differences in growth of transplantable ascites hepatoma among various lines of Donryu rat

A total of 48 Donryu rats from 8 colonies of 5 lines were inoculated intravenously with 10(7) cells of the ascites hepatoma strain AH 66. All the conventional rats of the lines D-1 and D-2 died between 9 and 15 days after inoculation with a good growth of implanted tumor cells. On the other hand, SPF rats of the lines A-1, B-1, C and E survived for 60 days showing complete rejection of the implanted tumor cells. A 50% of conventionalized ex-SPF rats of the lines A-2 and B-2, which had been once established as SPF colonies, and thereafter had been "re-conventionalized", rejected the tumor cells. The present observations indicate that the microbial conditions of the animal, e.g. whether the animal is SPF or not, might play an important role in the growth of the implanted ascites hepatoma.     

IS421, a new insertion sequence in Escherichia coli

The nucleotide sequence of a new insertion sequence (IS) in Escherichia coli, IS421, was determined. It is 1340 bp long and contains inverted repeats of 22 bp at its termini. It is flanked by 13 bp direct repeats apparently generated upon insertion. There are two ORFs longer than 200 bp in IS421. One can encode a polypeptide of 371 amino acids (aa) and the other, which is on the other strand, can encode a polypeptide of 102 aa. The C-terminal part of the 371 aa polypeptide shows some homology to that of transposases encoded in some other known IS elements. The copy number of IS421 in chromosomal DNA was 4 for E. coli K-12 and B, and 5 for E. coli C, as determined by the Southern hybridization of restriction fragments.     

A pertussis toxin-sensitive GTP-binding protein plays a role in the G0-G1 transition of rat hepatocytes following establishment in primary culture

Acute spontaneous c-myc gene expression and sustained increase of a GTP-binding protein(s) (G-protein) which is sensitive to islet-activating protein (IAP), pertussis toxin, occurred early during primary culture of adult rat hepatocytes. Following these earlier events, DNA synthesis was demonstrated in response to EGF and insulin. Addition of IAP immediately after plating of primary cultures inhibited c-myc expression and the hormone-induced DNA synthesis. Addition at 24 h or later following cell inoculation, however, produced only weak effects on DNA synthesis, even though the IAP-sensitive G-proteins were completely inactivated. We conclude that the IAP-sensitive G-protein(s) plays a role in the earlier process(es) of the G0-G1 transition, which is essential for the initiation of growth factor-dependent DNA synthesis.     

Cell swelling induced by the permeant molecules urea or glycerol induces immediate high amplitude thyrotropin and prolactin secretion by perifused adenohypophyseal cells

The permeant molecules, urea and glycerol, evoked a prompt secretory burst of TSH and PRL when added to the extracellular medium of acutely dispersed anterior pituitary cells. Secretion of both hormones was proportional to the concentration of urea or glycerol between 26 and 104 mM (r greater than 0.89, P less than 0.001). Equivalent concentrations of the impermeant molecule, mannitol, did not induce secretion. The acute TSH and PRL secretory responses to TRH, hyposmolarity, and permeant molecules were qualitatively indistinguishable. These data support our hypothesis that cell swelling and resultant plasmalemma expansion is a potent inducer of hormone secretion. Since the secretory response to permeant molecules was not reduced in a Ca2+-free medium containing 0.1 mM EGTA, an increase in Ca2+ transport across the plasmalemma to raise cytosol Ca2+ concentration does not appear involved.     

Mutagenesis of human granulocyte colony stimulating factor

To define the structure-function relationship, we have made a number of mutants of human granulocyte colony-stimulating factor (hG-CSF) by in vitro mutagenesis. The results indicate that most of the mutations located in the internal and C-terminal regions of the molecule abolished the activity, whereas the mutants without N-terminal 4, 5, 7, or 11 amino acids retained the activity. N-terminal amino acids were also altered by cassette mutagenesis using a synthetic oligonucleotide mixture. Among them, KW2228, in which Thr-1, Leu-3, Gly-4, Pro-5 and Cys-17 were respectively substituted with Ala, Thr, Tyr, Arg and Ser, showed more potent granulopoietic activity than that of intact hG-CSF both in vitro and in vivo.     

The direct activation of human multidrug resistance gene (MDR1) by anticancer agents

Enhanced expression of a multidrug-resistance gene (MDR1) is observed in some cancer patient, but any regulatory mechanisms of MDR1 gene expression in this phenomenon is not yet known. In this study, the regulation of MDR1 gene was analysed by transient expression assays in the presence of anticancer agents. We found that MDR1 promoter could be activated directly on the addition of anticancer agents including vincristine, daunomycin, adriamycin and colchicine. The results suggest that the level of MDR1 mRNA expression is associated with previous chemotherapy, including drugs that select the multidrug resistance phenotype.     

Effect of cell cholesterol content on apolipoprotein B secretion and LDL receptor activity in the human hepatoma cell line, HepG2

Human hepatoma HepG2 cells were used to study the effects of cholesterol loading and depletion on apolipoprotein B (apoB) secretion and low-density lipoprotein (LDL) receptor activity. Exposure of HepG2 cells to cholesterol and oleic acid, which elevated intracellular cholesterol levels, stimulated apoB secretion and reduced receptor-mediated uptake of LDL, whereas recombinant complexes of apolipoprotein A-I with dimyristoylphosphatidylcholine, which depleted the cellular cholesterol pool, inhibited apoB secretion and up-regulated LDL receptors. Significant negative correlation (r = -0.92, P less than 0.001) between the levels of apoB secretion and LDL uptake was found. These data suggest that the cholesterol content of the cells may induce concomitant changes in apoB secretion and LDL receptor activity.