Studies on the regulation of cholesterol 7 alpha-hydroxylase and HMG-CoA reductase in rat liver: effects of lymphatic drainage and ligation of the lymph duct

Lymphatic drainage leads to a significant stimulation of both the cholesterol 7 alpha-hydroxylase and HMG-CoA reductase activity in rats (Bj?rkhem et al. 1978. Biochem. Biophys. Res. Commun. 85: (532-540). This finding was confirmed here and it was also shown that ligation of the lymph duct leads to a similar but less pronounced effect. Ligation of the lymph duct or lymph fistulation of bile duct-ligated or cholestyramine-treated rats did not further increase 7 alpha-hydroxylase or the HMG-CoA reductase activity. However, treatment of lymph fistula rats with cholestyramine led to a significant further stimulation of both 7 alpha-hydroxylase and HMG-CoA reductase activity. Intravenous infusion of lymph into bile fistula rats led to a significant inhibition of both cholesterol 7 alpha-hydroxylase activity and HMG-CoA reductase activity. A corresponding infusion of cholesterol-enriched Intralipid led to inhibition of HMG-CoA reductase without effect on cholesterol 7 alpha-hydroxylase activity. The results show that cholesterol 7 alpha-hydroxylase is feedback-regulated by bile acids in a situation where the flux of cholesterol to the liver is interrupted also. The possibility is discussed that there is a factor in the lymph that down-regulates cholesterol 7 alpha-hydroxylase. If such a factor exists, it requires an intact enterohepatic circulation for its effect. The stimulatory effect of cholestyramine on HMG-CoA reductase also in lymph fistula rats shows that the previously demonstrated suppressive effect of bile acids on HMG-CoA reductase is not only due to the effect of bile acids on intestinal absorption of cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanism of intestinal formation of deoxycholic acid from cholic acid in humans: evidence for a 3-oxo-delta 4-steroid intermediate

12 alpha-Hydroxy-3-oxo-4-cholenoic acid coupled to an adenosine nucleotide has been shown to be a metabolite of cholic acid in the intestinal anaerobic bacteria, Eubacterium species VPI 12708 (1987. J. Biol. Chem. 262: 4701-4707) and it has been suggested that this may be an intermediate in the conversion of cholic acid into deoxycholic acid. The possibility that the intestinal conversion of cholic acid into deoxycholic acid involves a 3-oxo-delta 4-steroid as an intermediate has been studied in the present work by use of [3 beta-3H]- and [5-3H]-labeled cholic acid. Whole cells as well as cell extracts of Eubacterium sp. VPI 12708 catalyzed conversion of [3 beta-3H] + [24-14C]cholic acid into deoxycholic acid with loss of about 50% of 3H label. When unlabeled chenodeoxycholic acid (20 microM) was added along with [3 beta-3] + [24-14C]cholic acid, then approximately 85% of the [3 beta-3H]-labeled was lost from deoxycholic acid. After administration of the same mixture to two healthy volunteers, deoxycholic acid could be isolated that had lost 81 and 84%, respectively, of the 3H label. Conversion of a mixture of [5-3H]- and [24-14C]labeled cholic acid by the above intestinal bacteria or cell extracts led to loss of 79-94 of the [5-3H] label.(ABSTRACT TRUNCATED AT 250 WORDS)     

Trade-off among antiherbivore defences in a south american blackberry (Rubus bogotensis)

Summary The idea of trade-offs among antiherbivore defences in plants is examined using data from a South American blackberry (Rubus bogotensis). Two distinct morphs of R. bogotensis, one with glandular trichomes and one without, were compared with respect to leaf toughness, number of prickles and prickle length. The two morphs were sympatric and grew under similar environmental conditions. The morph lacking trichomes had significantly tougher leaves and also tended to have more and longer prickles. Bioassay showed that Ithomiid larvae fed to a lesser extent on tough leaves than on more tender ones. Correlations between antiherbivore defences within each phenotype revealed three significant or almost significant negative relationships. The comparisons support the hypothesis that trade-offs exist among antiherbivore defences.     

Inhibition of zeaxanthin formation and of rapid changes in radiationless energy dissipation by dithiothreitol in spinach leaves and chloroplasts

Dithiothreitol, which completely inhibits the de-epoxidation of violaxanthin to zeaxanthin, was used to obtain evidence for a causal relationship between zeaxanthin and the dissipation of excess excitation energy in the photochemical apparatus in Spinicia oleracea L. In both leaves and chloroplasts, inhibition of zeaxanthin formation by dithiothreitol was accompanied by inhibition of a component of nonphotochemical fluorescence quenching. This component was characterized by a quenching of instantaneous fluorescence (F_o) and a linear relationship between the calculated rate constant for radiationless energy dissipation in the antenna chlorophyll and the zeaxanthin content. In leaves, this zeaxanthin-associated quenching, which relaxed within a few minutes upon darkening, was the major component of nonphotochemical fluorescence quenching determined in the light, i.e. it represented the `high-energy-state' quenching. In isolated chloroplasts, the zeaxanthin-associated quenching was a smaller component of total nonphotochemical quenching and there was a second, rapidly reversible high-energy-state component of fluorescence quenching which occurred in the absence of zeaxanthin and was not accompanied by F_o quenching. Leaves, but not chloroplasts, were capable of maintaining the electron acceptor, Q, of photosystem II in a low reduction state up to high degrees of excessive light and thus high degrees of nonphotochemical fluorescence quenching. When ascorbate, which serves as the reductant for violaxanthin de-epoxidation, was added to chloroplast suspensions, zeaxanthin formation at low photon flux densities was stimulated and the relationship between nonphotochemical fluorescence quenching and the reduction state in chloroplasts then became more similar to that found in leaves. We conclude that the inhibition of zeaxanthin-associated fluorescence quenching by dithiothreitol provides further evidence that there exists a close relationship between zeaxanthin and potentially photoprotective dissipation of excess excitation energy in the antenna chlorophyll.     

Iodide transport in primary cultured thyroid follicle cells: evidence of a TSH-regulated channel mediating iodide efflux selectively across the apical domain of the plasma membrane.

The transport of iodide was studied in porcine thyroid follicle cells cultured in bicameral chambers. The continuous layer of polarized follicle cells, joined by tight junctions, formed a diffusion barrier between the two compartments (apical and basal) of the culture chamber. Uptake and efflux of 125I- at either surface (apical and basolateral) of the cells were thus possible to determine. Protein binding of iodide was inhibited by methimazole (10(-3) M) in all experiments. Radioiodide was taken up by the cells from the basal medium in a thyroid-stimulating hormone (TSH)-dose dependent manner with a maximal cell/medium ratio of 125I- of about 50 in cultures prestimulated with 0.1 to 1 mU/ml for 2 days. This uptake was inhibited by perchlorate and ouabain. In contrast, 125I- was not taken up from the apical medium. In preloaded cells, iodide efflux was rapidly (within 1-2 min) and dose-dependently (0.1-10 mU/ml) stimulated by TSH. Bidirectional measurements revealed that TSH stimulated iodide efflux in apical direction, leaving efflux in basal direction unchanged. In experiments with continuous uptake of label from the basal compartment, the TSH-stimulated efflux in apical direction had a duration of 4 to 6 min and resulted in a reduction in the cellular content of radioiodide by up to 80%. Decreased levels of cellular 125I- remained for at least 15 min after TSH addition. From our observations we conclude that the TSH-regulated uptake and efflux of iodide take place at opposite surfaces of the porcine thyroid follicle cell. Acutely stimulated iodide efflux is not the result of an increased permeability for iodide in the entire plasma membrane but only in the apical domain of this membrane. This implicates the presence of an iodide channel mediating TSH-stimulated efflux across the apical plasma membrane of the follicle cell. The mechanism is suggested to facilitate a vectorial transport of iodide in apical direction, i.e., to the lumen of the intact follicle.     

Immuno-histochemical and -cytochemical Evidence Suggesting the Presence of Campylobacter jejuni and Campylobacter coli in Cases of Porcine Intestinal Adenomatosis

Antisera against a number of Campylobacter species were used in immuno-histochemical and -cytochemical studies on cases of porcine intestinal adenomatosis. Avidin-biotin-complex (ABC) and streptavidin immunoperoxidase methods were used on formalin-fixed, paraffin-embedded and frozen sections. Protein A gold method was used on formaldehyde fixed and frozen sections for immuno-cytochemistry. The antisera used were raised in rabbits by subcutaneous or intravenous injection of living or formalin treated organisms. Antisera against different serotypes of the thermotolerant, catalase positive Campylobacters, Campylobacter jejuni and Campylobacter coli gave positive reactions in the immuno-histochemical studies. The staining was found in intestinal epithelial cells both in the ileum and in the colon and was restricted to the apical cytoplasm of adenomatous epithelial cells. The staining had a granular pattern, the positive structures sometimes having the shape of Campylobacter. Epithelial cells in areas with normal differentiation of goblet cells did not stain. In contrast, no staining resulted with antisera against Campylobacter sputorum subsp. mucosalis and Campylobacter hyointestinalis. Immuno-cytochemistry, using antisera against Campylobacter jejuni showed that the positive staining in altered epithelial cells were restricted to intracellular organisms having a structure resembling Campylobacter spp.     

A Case of Neospora Associated Bovine Abortion in Sweden

Neospora caninum is a recently recognized protozoan organism that causes fatal neuromuscular disease in dogs and abortions and stillbirths in cattle and other animals (Dubey & Lindsay 1993). The parasite is morphologically similar and phylogenetically very closely related to the cyst-forming coccidium Toxoplasma gondii (Ellis et al. 1994, Holmdahl et al. 1994). This group of parasites has a two-host life cycle principally involving a carnivorous definitive host and a herbivorous or omnivorous intermediate host. However, with N. caninum, there is as yet no knowledge of any definitive host harbouring sexual stages of the parasite. The only known route of transmission is vertical from mother to foetus (Dubey & Lindsay 1993).     

Interactions among juveniles of two freshwater crayfish species and a predatory fish

Two freshwater crayfish species, Astacus astacus L. and Pacifastacus leniusculus Dana, co-occur in some Swedish lakes. Observational studies indicate that the introduced, North American species P. leniusculus may gradually replace the native A. astacus, but the mechanism behind the replacement is not known. This study examined the direct effects of interspecific competition between the crayfish, and indirect effects of competitive interactions and fish (European perch, Perca fluviatilis L.) predation. Three different experiments with young-of-the-year (YOY) crayfish were performed. P. leniusculus was strongly dominant over similar-sized A. astacus in interference competition for shelter in a laboratory experiment. However, in a 35-day experiment in outdoor pools, A. astacus growth and survival were about equally affected by interactions with conspecifics and P. leniusculus. In contrast, P. leniusculus was significantly more affected by intraspecific competition than by competition with A. astacus, suggesting asymmetric competition between the two species. The presence of perch in outdoor ponds with mixed-species groups of the two crayfish species resulted in considerably higher predation rates on A. astacus than on P. leniusculus. Both species showed strong antipredator responses to perch by increasing refuge use. I suggest that higher perch predation rates on A. astacus originate from P. leniusculus being the superior species in interspecific competition for shelter. Because of displacement from refuges, A. astacus individuals become more exposed to the predator. This indirect effect of interactions among the two cray-fish species and the predator may be important in the observed in situ replacement of A. astacus by P. leniusculus.     

Habitat shift in roach (Rutilus rutilus) induced by pikeperch (Stizostedion lucioperca) introduction: predation risk versus pelagic behaviour

Changes in the fish community structure and habitat use were followed after the introduction of pikeperch (Stizostedion lucioperca) to the roach-dominated Lake Gjersjøen. Quantitative echosounding showed that the density of juvenile roach (Rutilus rutilus) was dramatically reduced in pelagic areas, from 12 000–15 000 fish/ha to 250 fish/ha, while total fish density remained unchanged in littoral areas. At the same time, the habitat segregation between different size groups of roach was altered as larger roach utilized the pelagic zone after pikeperch introduction. The loss of the pelagic refuge for juvenile roach increased the availability of juvenile roach to littoral predators, notably perch. In littoral areas, the fish community changed from one dominated by roach (> 95%) to one dominated by perch (> 50%).     

Characterization of a non-detergent PS II-cytochrome b/f preparation (BS)

A non-detergent photosystem II preparation, named BS, has been characterized by countercurrent distribution, light saturation curves, absorption spectra and fluorescence at room and at low temperature (–196°C). The BS fraction is prepared by a sonication-phase partitioning procedure (Svensson P and Albertsson P-Å, Photosynth Res 20: 249–259, 1989) which removes the stroma lamellae and the margins from the grana and leaves the appressed partition region intact in the form of vesicles. These are closed structures of inside-out conformation. They have a chlorophyll a/b ratio of 1.8–2.0, have a high oxygen evolving capacity (295 mol O₂ per mg chl h), are depleted in P700 and enriched in the cytochrome b/f complex. They have about 2 Photosystem II reaction centers per 1 cytochrome b/f complex.The plastoquinone pool available for PS II in the BS vesicles is 6–7 quinones per reaction center, about the same as for the whole thylakoid. It is concluded, therefore, that the plastoquinone of the stroma lamellae is not available to the PS II in the grana and that plastoquinone does not act as a long range electron transport shuttler between the grana and stroma lamellae.Compared with Photosystem II particles prepared by detergent (Triton X-100) treatment, the BS vesicles retain more cytochrome b/f complex and are more homogenous in their surface properties, as revealed by countercurrent distribution, and they have a more efficient energy transfer from the antenna pigments to the reaction center.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F_v variable fluorescence - LHC light-harvesting complex - PpBQ phenyl-p-benzoquinone - PQ plastoquinone pool - P700 reaction center of PS I - PS I, PS II Photosystem I, II - Q_A first bound plastoquinone accepter - RC reaction centre