Hexokinase and 'glucokinase' in liver metabolism

Rat liver contains four hexokinase isoenzymes, one of which, despite often being called 'glucokinase', is no more specific for glucose than the others. However, it does differ from them in displaying a sigmoid kinetic response to glucose, requiring much higher glucose concentrations for activity, and being insensitive to physiological concentrations of glucose 6-phosphate.     

Stress induced changes in testis function

The mechanism through which chronic stress inhibits the hypothalamic-pituitary-testicular axis has been investigated. Chronic restraint stress decreases testosterone secretion, an effect that is associated with a decrease in plasma gonadotropin levels. In chronically stressed rats there was a decrease in hypothalamic luteinizing hormone-releasing hormone (LHRH) content and the response on plasma gonadotropins to LHRH administration was enhanced. Thus the inhibitory effect of chronic stress on plasma LH and FSH levels seems not to be due to a reduction in pituitary responsiveness to LHRH, but rather to a modification in LHRH secretion. It has been suggested that beta-endorphin might interfere with hypothalamic LHRH secretion during stress. Chronic immobilization did not modify hypothalamic beta-endorphin, while an increase in pituitary beta-endorphin secretion was observed. Since we cannot exclude that changes in beta-endorphin secreted by the pituitary or other opioids may play some role in the stress-induced decrease in LHRH secretion, the effect of naltrexone administration on plasma gonadotropin was studied in chronically stressed rats. Naltrexone treatment did not modify the decrease in plasma concentrations of LH or FSH. These findings suggest that the inhibitory effect of restraint on the testicular axis is exerted at hypothalamic level by some mechanism other than opioids.     

Influence of luteinizing hormone-releasing hormone agonists on human mammary carcinoma cell lines and their xenografts

The specific binding of luteinizing hormone-releasing hormone (LH-RH) agonist in estradiol-dependent MCF-7 and estradiol-independent MDA-MB-231 human breast cancer cells has been studied using [3H]Ovurelin [(D-3H-Phe6),des-Gly10-LH-RH- ethylamide]. The results of Scatchard analyses suggest the presence of a single class of receptor sites, both in cell suspensions and membrane fractions. Evaluation of these peptide receptors appears to reflect additional characteristics of biological behaviour of these human breast cancer cells. The synthetic LH-RH agonist Ovurelin [(D-Phe6),des-Gly10-LH-RH-ethylamide] can directly interfere (25-30%) with the proliferation of MDA-MB-231 human breast cancer cells in culture. The inhibitory effect of Ovurelin in vitro was negligible in the MCF-7 cell line. In the in vivo experiments the treated immunosuppressed mice bearing either MCF-7 or MDA-MB-231 xenografts responded to the high-dose LH-RH analogue Zoladex depot and Decapeptyl depot therapy. Since the MDA-MB-231 tumour was found to be ER-negative it seems possible that the regression of this xenograft results from the direct antitumor action of the LH-RH agonist.     

Chromosome banding study of the golden loach,Sabanejewia aurata balcanica from Slovakia (Cobitidae)

The karyotype of a subspecies of the golden loach,Sabanejewia aurata balcanica from eastern Slovakia was studied by conventional Giemsa staining, Ag-NOR staining, and C-banding. The diploid chromosome number was 2n = 50. The karyotype comprised 2 pairs of metacentric, 6 pairs of submetacentric and 17 pairs of subtelocentric to acrocentric chromosomes. Both metacentric pairs and 2 large subtelocentric pairs had massive pericentromeric blocks, while all other elements had only weak blocks of heterochromatin. The NORs were localized on the short arms of one middle-sized subtelocentric pair. The karyotype ofS. a. balcanica differs from that ofS. aurata kubanica, suggesting chromosomal polymorphism of this widely distributed, polytypic cobitid species. The polymorphic karyotypes of the golden loach may thus demonstrate transient stages, linking primitive and advanced cobitid karyotypes.     

Selected chromosome counts of the Czechoslovak flora III

Chromosome numbers compared with as yet published data are given for the following 12 Phanerogams (both native species and aliens) from Czechoslovakia:Ambrosia trifida L.,Cardamine chelidonia L.,Dephne cneorum L.,Epipactis albensis Nováková etRydlo,Linum flavum L.subsp flavum, Lunaria rediviva L.,Nepeta grandiflora M.BIEB.,Reseda luteola L.,Thlaspi montanum L.,Tithymalus salicifolius (Host)Klotzsch etGarcke,Tithymalus virgultosus (Klokov) Holub andVerbascum speciosum Schrad. subsp.speciosum. The chromosome number 2n=40 is presented for the first time in autogamousEpipactis albensis Nováková etRydlo. New chromosome numbers were found inCardamine chelidonia L. (2n=32) and inTithymalus salicifolius (Host) Klotzch etGarcke (2n=40). Known but less frequent cytotypes are reported inLinum flavum L. subsp.flavum (2n=28) and inVerbascum speciosum Schrad. subsp.speciosum (2n=30).     

The planktonic rotifers of the estuarine lagunar complex of Suape (Pernambuco,Brazil)

We studied spatial and temporal distribution, abundance, diversity, equitability and species associations of the rotifers of the estuarine area of Suape (Pernambuco-Brazil), based on plankton samples collected according to the tidal regime at 11 fixed stations in Suape Bay and the estuaries of Massangana, Tatuoca and Ipojuca Rivers, during February (dry season) and July (rainy season) of 1978. Concurrent hydrological and climatological data were taken. Eight species groups were established. In general, rotifers dominated in the Ipojuca River estuary and stations subject to its influence. Greatest community similarities were observed among nearby stations, during the same tide and season. Hydrological factors influenced the occurrence and distribution of some species, and a close correlation between phytoplankton and rotifers was observed. Pollution in Ipojuca River contributed to diversity.     

In vitro studies on the growth of Shigella sonnei by Lactobacillus casei and Lact. acidophilus.

The inhibitory effect of lactobacilli on growth of Shigella sonnei was studied. The effect was not due to pH alone, as addition of hydrochloric, lactic or acetic acids to culture media did not inhibit the normal growth of the shigellas. The degree of inhibition was measured by disc assay and showed that the inhibitory substance(s) can be extracellular and diffusible, varying the degrees of inhibition depending on the media tested. When broth was inoculated with mixed cultures of Lactobacillus and Shigella strains, the inhibition began at 6 h and the death phase at 9 h. The higher inhibition was produced by the mixture of lactobacilli (35.5 +/- 2.5% at 6 h culture, 57.4 +/- 1.9% at 9 h and 91.2 +/- 1.2% at 14 h). The degree of inhibition was higher when the relationship pathogen : lactobacilli was 1:10(3). The specific growth rate of lactobacilli and shigella was different in pure or mixed cultures. When the lactobacillus alone was grown for 12 h and the shigellas then added, the numbers of shigellas began to decrease immediately at 37 degrees C. This work shows that the Lactobacillus strains employed in fermented milk can be used to inhibit the growth of Sh. sonnei.     

UV-induced mutability in repair-deficientrad6-1 strains ofSaccharomyces cerevisiae is caused by a suppressor gene

TheRAD6 gene is a multifunctional gene required for DNA repair, induced mutagenesis and sporulation. The survival and revertibility of two loci in fourrad6-1 mutant strains of different origin after UV irradiation were followed. As expected, all therad6-1 strains tested were more sensitive to UV radiation in comparison withRAD6 strains. The reversion frequency per survivor intrpl-289 andarg4–17 alleles was significantly higher in all fourrad6-1 mutant strains than in wild-type strains after equal doses of UV radiation. On the basis of genetic analysis we suggest that the phenomenon of increased frequency of induced mutagenesis is caused by a suppressor gene.     

Use of whey for production of exocellular polysaccharide by a mutant strain ofXanthomonas campestris

Growth and kinetics of the production of exocellular polysaccharide was studied in a mutant strain ofXanthomonas campestris lac ⁺ during cultivation in a submerged culture in a medium containing whey. The maximum production of the polymer was observed at the initial stage of the stationary growth phase of the culture. The mean production yield was about 1.4%. The results were comparable with those obtained during cultivation on a lactose medium. Translated by Č. Novotny