Role of platelet-activating factor in renal function in normal rats and rats with bilateral ureteral obstruction

Platelet-activating factor (PAF) is a powerful vasodilator with important effects on kidney function. It has been suggested that the renal effects of PAF are mediated by thromboxane A2 (TxA2). We examined the effect of PAF on renal function in sham-operated rats and rats that had undergone unilateral release of bilateral ureteral obstruction (BUO) of 24-hr duration, a condition in which the synthesis of TxA2 is increased. To eliminate systemic hemodynamic changes, PAF was infused directly into the left renal artery using the lowest dose that affected renal function (2.3 x 10(-13) moles/min). Infusion of PAF significantly decreased the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) in normal rats and rats with BUO. Normal (sham-operated) rats pretreated with an inhibitor of TxA2 synthesis also had a significant decrease in GFR after administration of PAF (ERPF also decreased, but not significantly). Rats with BUO pretreated with an inhibitor of TxA2 synthesis had significantly greater basal GFR and ERPF (increases of 72 and 171%, respectively) than untreated BUO rats. Administration of PAF to the former group further increased GFR and ERPF (by 37 and 39%, respectively; P less than 0.001). The role of endogenous PAF was evaluated by administering a specific PAF receptor antagonist. Sham-operated rats pretreated with high doses of the PAF receptor antagonist had significantly higher mean arterial pressure values than normal untreated rats, and had no decrease in GFR and ERPF during PAF infusion. Rats with BUO pretreated with the PAF antagonist had a significant, dose-dependent decrease in basal GFR and ERPF. These data suggest that endogenous PAF has a vasodilatory role in obstructive nephropathy. No significant differences in eicosanoid excretion in the urine corrected per GFR were observed during infusion of PAF in any of the groups examined. In BUO rats with intact TxA2 synthesis, exogenous administration of PAF decreased renal function, presumably through further increases in the production of TxA2. However, when TxA2 production was inhibited, PAF administration increased GFR and ERPF, presumably due to its unopposed vasodilatory properties. The data suggest an important role of PAF in the hemodynamic changes seen in obstructive nephropathy.     

Energetics of Anaerobic Sodium Transport by the Fresh Water Turtle Bladder

Certain of the metabolic events associated with anaerobic sodium transport by the isolated bladder of the fresh water turtle have been investigated. The data suggest that energy for this transport arises from glycolysis and that endogenous glycogen was the major and perhaps the sole source of substrate. The rate of anaerobic glycolysis, as determined by lactate formation, correlates well with the rate as determined by glycogen utilization. Using lactate formation as the index of anaerobic glycolysis, a linear relationship was observed between glycolysis and net anaerobic sodium transport. In the absence of sodium transport, glycolysis decreased by approximately 45 per cent. Tissue ATP concentrations were maintained at about the same level under anaerobic as under aerobic conditions. Finally if it is assumed that in the conversion of glycogen to lactate anaerobically, 3 moles of ATP are generated per mole of glucose residue, an average of over 15 equivalents of sodium were transported for every mole of ATP generated.     

Effect of imidazole on renal gluconeogenesis

The metabolic effects of imidazole were tested in rat renal cortex. Imidazole enhanced the activity of renal cortical phosphodiesterase in vitro. Imidazole inhibited glucose production in a dose-dependent fashion from a variety of substrates in the gluconeogenic pathway proximal to the triose phosphates. The stimulation in renal gluconeogenesis resulting from isoproterenol and parathyroid hormone was inhibited by imidazole. These changes correlated with an inhibition of the augmented levels of renal cortical cyclic AMP levels produced by these hormones. These studies indicate that imidazole is an effective activator of phosphodiesterase in intact renal cells and lend further support to the suggestion that the stimulation of renal gluconeogenesis produced by isoproterenol and parathyroid hormone is mediated by a release of cyclic AMP.     

A resistance gene analog useful for targeting disease resistance genes against different pathogens on group 1S chromosomes of barley,wheat and rye

Comparative sequence analysis of the resistance gene analog (RGA) marker locus aACT/CAA (originally found to be tightly linked to the multiallelic barley Mla cluster) from genomes of barley, wheat and rye revealed a high level of relatedness among one another and showed high similarity to a various number of NBS-LRR disease resistance proteins. Using the sequence-specific polymerase chain reaction (PCR), RGA marker aACT/CAA was mapped on group 1S chromosomes of the Triticeae and was associated with disease resistance loci. In barley and rye, the marker showed linkage to orthologous powdery mildew resistance genes Mla1 and Pm17, respectively, while in wheat linkage with a QTL against fusarium head blight (FHB) disease was determined. The use of RGA clones for R gene mapping and their role in the expression of qualitative and quantitative resistance is discussed.     

No sex at all? Extremely low genetic diversity in Gagea spathacea (Liliaceae) across Europe

Most vascular plant taxa are able to reproduce vegetatively in addition to sexual reproduction. Some plants even survive despite of (near to exclusive) sexual sterility. However, very few of these taxa are non-apomicts with a wider distribution range.     

Tree dispersion in oak-dominated forests along an environmental gradient

Summary Spatial pattern was analyzed in seventeen stands of oak-dominated forest to address the hypothesis that species tended to be aggregated under favorable conditions and widely spaced in xeric, nutrient poor conditions. Trees were sampled at 80–100 points in each stand with the distance-to-nearest neighbor method. Soil samples were collected in each stand for analysis of total nitrogen, total phosphorus, total potassium, soil pH, soil texture, and soil organic matter. Growing season precipitation was also recorded from climate stations near each stand. Quercus stellata (Wang.) dominated 10 stands, Q. marilandica (Muenchh.) dominated three stands and these species were codominant in four stands. Principal components analysis identified a soil texture/fertility gradient across the study area. Quercus stellata and all species combined were aggregated in most stands, whereas Q. marilandica was mostly randomly distributed within a stand. Small trees of all species combined tended to be aggregated and large trees were randomly dispersed in all but two stands, suggesting competition. Mean distance between large-large pairs was always greater than mean distance between small-small pairs in all stands, but this difference was only significant in one stand. Correlations between nearest neighbor distance and combined size of nearest neighbors were significant and positive in 12 of 17 stands. In all cases, however, slopes were shallow suggesting that competition is weak in these communities and has a limited effect on spacing of neighboring trees. Contrary to our hypothesis, trees were more aggregated on coarse-textured soils with low organic matter content. For all species combined, degree of aggregation was unrelated to growing season precipitation. Aggregation appears to be common in these forests because environmental stress in many stands reduces growth rates. Trees have not yet reached a size at which competition or other interactions can greatly increase interplant distances and reduce the degree of aggregation. A simple graphical model is developed to describe the relationship between patterns, stress and competition in plant communities.     

Sodium Transport in Turtle Erythrocytes : Apparent stimulation of exchange diffusion by anaerobiosis

Studies were performed on Na and K transport by red blood cells of the freshwater turtle under anaerobic and aerobic conditions. Although it had previously been assumed that cation transport in turtle red blood cells was dependent on respiration, the present data show greater Na efflux rates in N₂ than in O₂. However, ouabain inhibited Na transport by the same amount quantitatively in O₂ and N₂ gas phases. Thus there was no difference in ouabain-sensitive or "pump" Na transport rates. Na influx rates were higher in nitrogen than in air and potassium influx rates were not significantly different under aerobic and anaerobic conditions. Moreover in the absence of sodium in the bathing medium no difference between air and nitrogen could be discovered. Finally with ethacrynic acid plus ouabain there was an additional decrease in Na efflux but there was a persisting difference between air and nitrogen. These studies do not rule out the existence of a ouabain-insensitive ethacrynic acid-inhibitable flux; however, they suggest that at least part of the activation of Na efflux observed in N₂ was due to increased exchange diffusion.     

Does sex make a difference? Genetic diversity and spatial genetic structure in two co-occurring species of Gagea (Liliaceae) with contrasting reproductive strategies

Gagea lutea and G. spathacea are spring geophytes naturally co-occurring in woodlands, characterised by contrasting reproductive strategies probably caused by divergent ploidy levels. The hexaploid G. lutea relies on vegetative reproduction by subterranean bulbils in young stages but completely switches to sexual reproduction once a certain bulb size is attained. The nonaploid G. spathacea seems to be sterile and reproduces only vegetatively; the plants continue to form bulbils even in the rare event of flowering. This study used AFLP genotyping to investigate the consequences of these reproductive strategies for genetic diversity. For 150 and 100 samples from three Western Pomeranian populations of G. lutea and G. spathacea, respectively, AFLP fingerprints were analysed for three different spatial scales, the patch, the transect, and the region. Applying a threshold for genotypic identity of <0.05 simple matching distance, 22?C30 genets were detected in the three G. lutea populations, with all genets confined to single populations. Clonal genets consisted of 2?C9 samples and extended over up to 28?m, but never occupied the whole length of a transect; 67?C75% of all patches had different genets. Genetic distances between genets within populations were similar to those recorded between populations. Genotyping of G. spathacea revealed a single clonal genet for all three populations sampled within a distance of 30?km. The absent genetic diversity confirms the suspected sexual sterility. Gagea spathacea seems to be one of the few non-apomictic, fully clonal vascular plants able to occupy a significant range solely by dispersal of vegetative diaspores.     

Cytochrome P-450 pathway in renal function of normal rats and rats with bilateral ureteral obstruction.

Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) are decreased and mean arterial pressure (MAP) and renal vascular resistance (RVR) are increased after unilateral release of bilateral ureteral obstruction (BUO) of 24 hr duration. An imbalance between vasoconstrictor and vasodilator substances may explain these hemodynamic changes. We examined the role of the cytochrome P-450 pathway in this setting. After unilateral release of BUO, GFR and ERPF (ml/min/kg body wt) were significantly lower in these rats than in sham-operated rats (SOR) 1.14 +/- 0.09 vs 6.7 +/- 0.5 and 3.09 +/- 0.2 vs 23.5 +/- 3.4, respectively). BUO rats had significantly higher MAP (mm Hg) and RVR (mm Hg/ml/min/kg body wt) than SOR (155 +/- 5 vs 120 +/- 1 and 29.1 +/- 1.7 vs 3.2 +/- 0.4, respectively). SOR given 3-methylcholanthrene and beta-naphthoflavone to induce the cytochrome P-450 system had no significant changes in renal function, RVR, or MAP. SOR given ketoconazole to inhibit the cytochrome P-450 system had significantly lower GFR (4.8 +/- 0.5) than temporal control rats without significant changes in ERPF (21.2 +/- 4.6), MAP (127 +/- 6), or RVR (4.2 +/- 0.9). Rats with BUO given ketoconazole had lower but not significantly different GFR (0.84 +/- .1) and ERPF (2.61 +/- .4) than BUO controls. Values for MAP did not differ in BUO rats given ketoconazole versus BUO temporal controls. BUO rats given 3-methylcholanthrene and beta-naphthoflavone had significantly higher GFR and ERPF (2.01 +/- 0.24 and 6.66 +/- 1.36, respectively) and significantly lower RVR (14.7 +/- 3.9) than control rats with BUO; MAP was unchanged. Microsomal preparations from indomethacin-treated isolated kidneys obtained from BUO rats when compared with preparations obtained from SOR had significantly less activity of the P-450 cytochrome-dependent omega/omega-1 hydroxylase (103 +/- 6 vs 130 +/- 7 pmol hydroxyeicosatetraenoic acids produced per mg of protein/min, P < 0.02) and the P-450 cytochrome-dependent epoxygenase (11 +/- 0.3 vs 30 +/- 4 pmol lipoxyeicosatrienoic acids produced per mg of protein/min, P < 0.04). Indomethacin-treated microsomes prepared from kidneys of BUO rats converted significantly less 14C-arachidonic acid through the P-450-dependent hydroxylases (13.5 +/- 0.8 vs 17.0 +/- 0.1% of 14C-arachidonic acid converted to 19- and 20-hydroxyeicosatetraenoic acids, P < 0.02), and significantly less through the epoxygenases (1.4 +/- 0.4 vs. 3.8 +/- 0.5% of 14C-arachidonic acid converted to epoxyeicosatrienoic acids).(ABSTRACT TRUNCATED AT 400 WORDS)