Levels Of Po Research Articles

Modulation of the endocrine and immune systems by well-controlled hyperthermia equipment

Since high levels of hyperthermia induce immunosuppression to a certain extent (i.e., granulocytosis and lymphocytopenia) in patients, we applied mild hyperthermia in volunteers using equipment enabling well-controlled hyperthermia. Restricted control of rectal temperature at 39.4 (+/- 0.2) degrees C for 30 min was conducted and various parameters of the body were examined. The most prominent change observed during exposure to hyperthermia was elevated levels of pH and PO(2) in the blood, even in the venous blood. A transient elevation of ACTH, cortisol and growth hormone in the blood was also seen during this time. In parallel with this phenomenon, the number of total lymphocytes and those of its subsets (especially CD57(+) or CD56(+) NK cells and NKT cells) increased. More interestingly, the proportion of HLA-DR (MHC class II antigens) increased in NK and NKT cells, and their intensity on the surface of CD20(+) B cells increased. These results suggest that mild hyperthermia is important for modulation of the functions of the circulatory, endocrine and immune systems.

Nano DCPA-whisker composites with high strength and Ca and PO(4) release.

The main challenges facing composite restorations are secondary caries and bulk fracture. The objective of this study was to develop nano DCPA (dicalcium phosphate anhydrous)-whisker composites with high strength and Ca and PO(4) ion release to combat caries. Flexural strength for the nano DCPA-whisker composites at a nano DCPA:whisker mass ratio of 1:2 ranged from (148 +/- 9) MPa to (167 +/- 23) MPa, significantly higher than the (103 +/- 32) MPa of an inlay/onlay commercial control composite without Ca-PO(4) release. The nano DCPA-whisker composite released PO(4) to a concentration of (1.95 +/- 0.13) mmol/L and Ca of (0.68 +/- 0.05) mmol/L. Compared with previous conventional Ca- and PO(4)-releasing composites, the nano DCPA-whisker composites had strengths two-fold higher, and released comparable or higher levels of Ca and PO(4). In conclusion, combining nano-DCPA with whiskers yielded novel composites that released high levels of Ca and PO(4) requisite for remineralization. These high-strength composites may provide a unique combination of stress-bearing and caries-inhibiting capabilities.

Flow velocity affects internal oxygen conditions in the seagrass Cymodocea nodosa

The internal oxygen status of seagrass tissues, which is believed to play an important role in events of seagrass die-off, is partly determined by the rates of gas exchange between leaves and water column. In this study, we examined whether water column flow velocity has an effect on gas exchange, and hence on internal oxygen partial pressures ( pO 2) in the Mediterranean seagrass, Cymodocea nodosa. We measured the internal pO 2 in the horizontal rhizomes of C. nodosa in darkness at different mainstream flow velocities, combined with different levels of water column oxygen pO 2 using an experimental flume in the laboratory. Flow velocity clearly had an effect on the internal oxygen status. In stagnant, but fully aerated water the mean internal pO 2 was 6.9 kPa, corresponding to about 30% of air saturation. The internal pO 2 increased with increasing flow velocity reaching saturation of around 12.2 kPa (60% of air saturation) at flow velocities ≥7 cm s −1. Flow had a relatively larger influence on internal pO 2 at lower water column oxygen concentrations. By extrapolating linear relationships between internal and water column pO 2 in this experimental setup, rhizomes would become anoxic at a water column oxygen pO 2 of 4–4.5 kPa (∼20% of air saturation) in flowing water, but already at 6.4 kPa (∼30% of air saturation) in stagnant water. Water flow may play an important role for seagrass performance and survival in areas with poor water column oxygen conditions and may, in general, be of importance for the distribution of submerged rooted plants.

Preferential utilization of organic and inorganic sources of phosphorus by wheat plant

On soils of low P supply organic P (Po) makes up a similar or even larger part in soil solution than inorganic P (Pi). The ability of wheat (Triticum aestivum L., cv. Star) plants to hydrolyze and absorb this Po in comparison to similar concentrations of Pi was studied. Four concentration levels of Pi and Po were obtained by extracting two soils with deionized water in a ratio of 1:1 and concentrating the resulting filtrate by freeze drying to different degrees. The concentration of Pi varied between 5 and 36 μM and Po between 3 and 22 μM. Wheat seedlings were grown in these solutions for 12 and 24 h and acid and alkaline phosphatase activity determined. The reduction of Po concentration in solution expressed on a root length basis gave the rate of Po hydrolysis and the reduction in concentration of Pi and Po gave the P inflow into the roots. No alkaline phosphatase activity was detected. The activity of wheat root acid phosphatase increased with Po concentration in solution. Phosphorus uptake was 2 to 6 fold higher from Pi than from Po at similar concentrations of both. The rate of uptake from Pi, the inflow, as well as the rate of hydrolysis of Po increased linearly with concentration but at similar concentration the inflow was 2 to 4 times higher than the rate of Po hydrolysis. Results suggest that plants can utilize Po after hydrolysis by phosphatase, but Pi is more important and preferentially used by plants; Po may be essential for plant nutrition especially in high P-fixing soils.

Validation of quantitative BOLD MRI measurements in kidney: Application to unilateral ureteral obstruction

Blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) provides a measure of deoxyhemoglobin content and therefore an indirect measure of the partial oxygen pressure (pO(2)). The main purpose of this study was to examine the relationship between the apparent relaxation rate (R2*) in the pig kidney by BOLD imaging and renal tissue pO(2) levels measured directly by oxygen-sensitive microelectrodes. Second, BOLD imaging was applied to kidneys in pigs subjected to acute unilateral ureteral obstruction (UUO) to examine whether this condition is associated with changes in intrarenal oxygenation. Oxygen-sensitive microelectrodes were inserted in the cortex and medulla of pig kidneys (N= 6). Different arterial and intrarenal levels of pO(2) were obtained by stepwise changing the oxygen-to-nitrogen ratio supplied by a respirator. Simultaneous BOLD MRI measurements using an R2*-sensitive Echo Planar Imaging (EPI) sequence were performed on the contralateral kidney. In another group of pigs (N= 3) BOLD imaging was performed following 24 hours of UUO. When the inhaled oxygen fraction was 5% to 70%, R2* was linearly related to pO(2) levels (cortex DeltaR2*/DeltapO(2)=-1.2 ms(-1)kPa(-1), and medulla DeltaR2*/DeltapO2 =-1.7 ms(-1)kPa(-1)). Twenty-four hours of UUO was associated with an increased R2* in the cortex and a decreased R2* in medulla as compared with baseline, which remained augmented after the release of UUO, indicating that pO(2) levels were reduced in the cortex and increased in the medulla during and after release of obstruction. BOLD MRI provides noninvasive estimates of regional renal oxygen content and our study demonstrates that this technique may provide a useful tool in UUO which is associated with altered renal oxygen consumption.

Dynamics and availability of phosphorus in the rhizosphere of a temperate silvopastoral system

A field rhizosphere study was carried out over a period of 12 months on a 6-year-old silvopastoral trial in New Zealand. The trial comprised radiata pine (Pinus radiata) with lucerne (Medicago sativa) and perennial ryegrass (Lolium perenne) understoreys. The study was initiated because of the unique interrelationships between roots in silvopastoral systems and a paucity of understanding about the processes involved in phosphorus (P) dynamics in temperate silvopastoral systems. Improving our understanding in this area has important implications for nutrient management in silvopastoral systems. Rhizosphere soils were analysed to determine inorganic (Pi) and organic (Po) P fractions, macroporous resin Pi and Po, phosphatase enzyme activity, microbial biomass carbon and pH. Concentrations of labile Pi were consistently greater and Po lower in tree rhizosphere soil compared to the companion understorey, indicating that radiata pine when grown with a productive understorey mineralised Po to a greater extent than either understorey species. Tree rhizosphere soil from under lucerne and lucerne rhizosphere soil contained the lowest concentrations of total Pi and Po compared with tree under ryegrass and ryegrass rhizosphere soils. This was partly attributed to higher levels of phosphatase enzyme activity in the lucerne rhizosphere soils. The results suggest the combination of lucerne with radiata pine may enhance greater utilisation of soil P, although this requires further investigation. Lower levels of labile Po, and higher levels of labile Pi and phosphatase enzyme activity, were determined in tree and understorey lucerne and ryegrass rhizosphere soils in spring compared with autumn. This data confirmed that overall rates of soil organic P mineralisation are greatest in spring.

Mifepristone (RU 38486) influences expression of glycoprotein Po and morphological parameters at the level of rat sciatic nerve: in vivo observations

The observations here reported indicate that, in vivo, the expression of an important protein of peripheral myelin, the glycoprotein Po, is influenced by mifespristone (RU 38486), that is, an antagonist of progesterone (PR) and glucocorticoid (GR) receptor. In our experimental model, male rats have been treated at the first day of life with this antagonist and after repeated treatments, we have analyzed in the sciatic nerve of 20- (20d) and 30-day-old rats (30d) the mRNA and protein levels of Po. Moreover, expression of Po has also been analyzed in the sciatic nerve of animals treated during the first 30 days of postnatal life and then sacrificed at 90th day of life (90d). The results obtained have indicated that both mRNA and protein levels of Po decrease at 20d. Apparently, these effects seem to be transient because no changes are evident at the other two times of analysis. As shown by morphometric analysis, the treatment with RU 38486 is also able to induce morphological changes at the level of sciatic nerve. However, at variance to what is expected by an alteration of an important component of the myelin membranes like Po, no changes are evident at the level of the myelin compartment. On the contrary, a significant reduction of axon diameter in parallel to an increase in neurofilament (NF) density occurs since 30d. In conclusion, the present data seem to suggest that progestin and/or glucocorticoid signals are not only involved in the control of myelin compartment but also on the axon maintenance.

Actions of progesterone and its 5α-reduced metabolites on the major proteins of the myelin of the peripheral nervous system

The sciatic nerve, and the Schwann cells in particular, are able to synthesize progesterone and possess the enzymes forming the 5α-reduced and the 3α-5α-reduced derivatives of progesterone: dihydroprogesterone and tetrahydroprogesterone. Moreover, the progesterone receptor (PR) is present in the sciatic nerve and in Schwann cell cultures. These facts suggest that progesterone and its derivatives might play a role in the control of the synthesis of the two major proteins of the peripheral nervous system (PNS): the glycoprotein Po (Po) and peripheral myelin protein 22 (PMP22). We have shown that: (a) dihydroprogesterone enhances the low mRNA levels of Po in the sciatic nerve of aged male rats; (b) progesterone and its derivatives stimulate the gene expression of Po in the sciatic nerve of adult rats and in Schwann cell cultures; (c) tetrahydroprogesterone increases PMP22 gene expression in the sciatic nerve of adult rats and in Schwann cell cultures. In additional experiments, utilizing agonists and antagonists of PR and GABA A receptor, we have observed that progesterone and its derivatives control Po gene expression via the PR, while tetrahydroprogesterone modulates the expression of PMP22 through the GABA A receptor.

Effects of air bubbles and tube transportation on blood oxygen tension in arterial blood gas analysis.

Pneumatic tube transport has been reported to aggravate the error in partial pressure of oxygen (PO(2)) measurements caused by air bubbles. The aim of this study was to clarify the effect of manual and pneumatic tube methods of sample transportation and different amounts of air bubbles on arterial blood gas analysis. Blood gas samples from 15 patients and a pooled wasted blood mixture with 3 different levels of PO(2) were analyzed to determine the effects of air bubbles and manual versus pneumatic tube transportation on PO(2) levels. PO(2) increased significantly in samples containing 10% air bubbles and was exaggerated by pneumatic tube transport (from 115.63 +/- 9.31 mm Hg to 180.51 +/- 11.29 mm Hg, p < 0.001). In samples with low PO(2) ( approximately 30 mm Hg), the measurement was not aberrant regardless of the method of transportation or the amount of air bubbles contained in the specimen. However, in samples with medium and high PO(2) (> 70 mm Hg), aberrances in measurements were noted even with only 0.5% air bubbles and regardless of whether the sample was transported by manual methods or pressurized tube. The increments of PO(2) correlated positively with the amount of air introduced into the specimens. Thus, the measured PO(2) increased 8.13 and 31.77 mm Hg when 0.5% and 10% air bubbles were introduced, respectively, to samples with medium PO(2) (p < 0.05). The interaction between the amount of air bubbles and the method of transportation was significant (p < 0.001). Trapped air in the syringe should be expelled as thoroughly as possible, since the presence of only 1% air bubbles can result in aberrance in PO(2) measurement. Samples for blood gas analysis should be carried in ambient pressure to the laboratory because pneumatic tube delivery systems significantly aggravate the air bubble-related aberrance in PO(2) measurement.

Chronic hypoxia-induced morphological and neurochemical changes in the carotid body.

The carotid body (CB) plays an important role in the control of ventilation. Type I cells in CB are considered to be the chemoreceptive element which detects the levels of PO(2), PCO(2), and [H(+)] in the arterial blood. These cells originate from the neural crest and appear to retain some neuronal properties. They are excitable and produce a number of neurochemicals. Some of these neurochemicals, such as dopamine and norepinephrine, are considered to be primarily inhibitory to CB function and others, such as adenosine triphosphate, acetylcholine, and endothelin, are thought to be primarily excitatory. Chronic hypoxia (CH) induces profound morphological as well as neurochemical changes in the CB. CH enlarges the size of CB and causes hypertrophy and mitosis of type I cells. Also, CH changes the vascular structure of CB, including inducing marked vasodilation and the growth of new blood vessels. Moreover, CH upregulates certain neurochemical systems within the CB, e.g., tyrosine hydroxylase and dopaminergic activity in type I cells. There is also evidence that CH induces neurochemical changes within the innervation of the CB, e.g., nitric oxide synthase. During CH the sensitivity of the CB chemoreceptors to hypoxia is increased but the mechanisms by which the many CH-induced structural and neurochemical changes affect the sensitivity of CB to hypoxia remains to be established.

PHOSPHATE AND SULFATE RETENTION BY NONVOLCANIC SOILS WITH ANDIC PROPERTIES

Soils with andic properties have a high anion retention capacity, which is mainly related to the large amounts of active Al and Fe compounds that they contain. The phosphate (PO 4 ) and sulfate (SO 4 ) sorption capacity of soils with andic properties from Galicia, NW Spain, was investigated. Phosphate sorption experiments were conducted by adding 1.6, 16.1, and 48 mM KH 2 PO 4 to soils, and those of sulfate by adding 0.4 and 1.6 mM K 2 SO 4 (ratio of soil:solution, 1:10). The pH of the extracts was measured, as were the levels of PO 4 (only in the PO 4 experiments), SO 4 , Si, and dissolved organic carbon. The soils retained much higher amounts of PO 4 than of SO 4 . Surface horizons displayed a higher capacity than subsurface horizons for retaining PO 4 but not for retaining SO 4 . The PO 4 retention capacity was related to the sum of contents of oxalate extractable-Al (Al o ) and -Fe (Fe o ), which tended to increase with soil organic carbon content and was mainly attributed to the presence of Al-humus complexes. Sorption of PO 4 primarily produced displacement of dissolved organic carbon, Si, and SO 4 into solution and increases in solution pH, whereas sorption of SO 4 only generated increases in solution pH. The low ability of SO 4 anions to displace sorbed organic C mainly explains why surface horizons retained similar or even smaller amounts of SO4 than subsurface horizons, despite the higher Al o and Fe o contents of the former. The results emphasize the different affinities of PO 4 and SO 4 for reactive surfaces and the interaction of organic C in sorption processes.

Properties of Tablets Containing Granulations of Ibuprofen and an Acrylic Copolymer Prepared by Thermal Processes

The objective of this study was to investigate the properties of tablets containing granulations of ibuprofen (Ibu) and Ammonio Methacrylate Copolymer, Type B (Eudragit RS PO) prepared by hot-melt processing. Tablets were compressed from granules prepared by hot-melt granulation (HMG) or direct compression (DC). For the hot-melt extrusion (HME) process, tablets were prepared by cutting the extrudate, manually. The physicochemical properties of tablets were investigated using thermal analysis, powder X-ray diffraction analysis, tablet hardness, and drug dissolution. The effect of thermal treatment of tablets on the dissolution characteristics of Ibu was also investigated. The results demonstrated that the Ibu lowered the glass transition temperature (Tg) of the Eudragit RS PO and the softened polymer functioned as a thermal binder in the granulation. Ibu was demonstrated to be an effective plasticizer for Eudragit RS PO in the thermal processes. The efficiency of the granulation process increased with increasing levels of Eudragit RS PO in the powder blend. Higher levels of Eudragit RS PO in the tablets prepared by HMG or HME resulted in a decrease in the dissolution rate of the Ibu. An increase in the amount of Ibu in the tablets prepared by HMG or DC led to a decrease in the initial dissolution rate of the Ibu. Following the thermal treatment of the Ibu tablets prepared by HMG, the dissolution rate was significantly decreased due to structural changes in the tablets that resulted from the fusion and coalescence of plasticized polymer particles, causing a reduction in tablet porosity. The Ibu tablets prepared by HME demonstrated minimal changes in their release properties following thermal treatment even at temperatures higher than the Tg of the polymer. HME was shown to be a novel method to prepare matrix tablets and stable dissolution properties were obtained when tablets were stored at 40°C for 30 days.

Whole gut washout ameliorates the progression of acute experimental pancreatitis

Background: Septic complications are mainly responsible for deterioration of a patient with acute pancreatitis. Intestinal tract is accepted as the main source of pancreatic or peripancreatic infection. Material andmethods: Acute pancreatitis was induced in 40 Sprague-Dawley rats by ligation of the main biliopancreatic duct. Animals were divided into two groups. The first group of animals (n = 20) received high volume polyethylene glycol-3500 (GoLYTELY) for 6 hours through a silastic catheter introduced into the proximal part of the jejunum from a puncture gastrostomy during the initial laparotomy. The second group animals (n = 20) did not receive any treatment. Half of the animals from each group were sacrificed 72 hours later and tissue samples were taken from mesenteric lymph nodes, pancreas, spleen, and liver for bacteriologic cultures. Cecum cultures were also prepared. Blood samples at 72 hours were obtained for the measurement of amylase, lactic dehydrogenase (LDH), lactic acid, alanine aminotransferase (ALT), glucose, calcium, arterial pH, base excess, partial oxygen pressure, bicarbonate, leucocyte count, and hematocrit levels. The pancreas was examined histopathologically. The remaining half of the animals from each group were allowed to survive until death. Results: The levels of amylase, LDH, ALT, lactic acid, pH, pO 2, bicarbonate and base excess for the rats in group I were significantly lower when compared with the rats in group II ( P <0.05). Positive mesenteric lymph node cultures were detected in 30% of group I animals whereas they were positive in 90% of group II animals ( P = 0.0198). Distant organ cultures were positive in 8 animals (liver 5, spleen 2, pancreas 1) in group II, whereas only one positive distant organ culture (liver) was established in group I ( P >0.05). Histopathological scoring observed in the pancreas were less severe for the rats in group I when compared with the rats in group II ( P = 0.012). The rats in group I survived longer than the rats in group II (median survival 6.8 days versus 17.3 days, P <0.001). Conclusions: Whole gut washout with high-volume polyethylene glycol in pancreatitis reduced the blood levels of enzymes and increased the survival. Whole gut washout for acute pancreatitis appears effective to ameliorate the prognostic factors in blood and this modality may be a promising treatment method in acute pancreatitis.

Factors influencing tissue concentration of vascular endothelial growth factor in colorectal carcinoma

OBJECTIVE: Vascular endothelial growth factor (VEGF) promotes proliferation of various tumor cells by stimulating angiogenesis. Experimentally, hypoxia and energy depletion are known to induce angiogenesis by increasing VEGF expression. We investigated whether factors reflecting the general condition of the patients influence the tissue concentration of VEGF in colorectal carcinoma. METHODS: Tissue concentrations of VEGF in 81 colorectal carcinomas, 81 normal mucosas, and 30 colonic adenomas were determined. The expressions of VEGF and its receptor in cancer tissue were evaluated immunohistochemically. For the assessment of the general preoperative condition of the patients, the nutritional status was evaluated and arterial blood gas was analyzed. RESULTS: The mean concentration of VEGF in the cancer tissue was significantly higher than that in the normal colonic mucosa and colonic adenoma. Tumor size, histological grade, serum cholinesterase, and arterial level of PO 2 were the independent factors that influenced the tissue concentration of VEGF in colorectal cancer. Immunohistochemically, the VEGF-positive cancer tended to have an increased expression of VEGF receptor, kinase insert domain–containing receptor (KDR). In patients with positive KDR in the tumor, the arterial levels of PO 2 and O 2 saturation were significantly lower than those in patients without its expression. CONCLUSION: Tissue content of VEGF or expression of KDR in colorectal carcinoma may be associated with disease status, including nutritional status, systemic oxygenation, and tumor progression. The systemic-local regulating mechanism of VEGF or KDR may play an important role in the constant growth of tumor cells, especially in wasted colorectal cancer patients.

Inhibition of CD11-CD18 complex prevents acute lung injury and reduces mortality after peritonitis in rabbits.

Acute lung injury is frequent after severe peritonitis. The aim of this study was to investigate whether inhibition of the adhesion molecule CD11-CD18 on polymorphonuclear leukocytes (PMNs) would have any beneficial effects on pulmonary function and mortality in an animal model reproducing these clinical conditions. Acute peritonitis was induced in 36 rabbits by intraperitoneal injection of zymosan (0.6 g/kg) suspended in mineral oil; 20 were pretreated with a murine-specific IgG2a anti-CD18 monoclonal antibody, 16 (controls) with nonspecific purified murine IgG (1 mg/kg). The animals were followed for 10 d, then killed for histologic examination of the lungs. Blood samples were taken on Days 0, 1, 3, 7, and 10 for red blood cell (RBC), white blood cell (WBC), and platelet counts, pH, PO(2), PCO(2), carbon dioxide content (HCO(3)(-)) measurements, and renal and liver tests. Treatment with the anti-CD18 monoclonal antibody reduced mortality by approximately 40% (p < 0.05). PO(2) was higher in these treated animals than in the control animals throughout the study (p < 0.05 on Day 1, 3, and 10). On Day 1 control animals had significant leukopenia, whereas anti-CD18-treated animals had a moderate increase of the number of circulating WBC compared with baseline values (p < 0.05 between groups). The lungs of the anti-CD18-treated animals showed minor signs of inflammation and PMN infiltration whereas controls had interstitial and intra-alveolar edema and a large number of granulocytes. Quantification of PMNs by morphometry showed that there were constantly less granulocytes in the lungs of the animals treated with the anti-CD18 antibody (p < 0.001). PMN infiltration correlated with the levels of PO(2) (p < 0.001). Lung tissue of anti-CD18-treated rabbits contained less malonyldialdehyde, a by-product of membrane lipid peroxidation by PMN oxygen radicals (950 +/- 120 versus 1,710 +/- 450 pM/mg of protein) and, conversely, more of the antioxidant alpha-tocopherol (136 +/- 22 versus 40 +/- 9 ng/mg of protein), than the control rabbits (p < 0.01). In this particular model of ARDS the monoclonal antibody against the CD11-CD18 complex had a beneficial effect, reducing PMN infiltration and oxygen radical release in the lungs, preventing alveolocapillary membrane damage, improving gas exchange and, finally, significantly reducing mortality.

Mechanical properties of bioactive amorphous calcium phosphate/methacrylate composites

Objectives. The aim of this study was to determine whether amorphous calcium phosphate (ACP)-containing composites, which have the ability to release mineralizing levels of Ca and PO 4 ions, have appropriate mechanical properties for use as base and lining materials. Methods. Composites of pyrophosphate-stabilized ACP particulates (mass fraction of 40%) and photo-activated methacrylate resins (mass fraction of 60%) were tested for biaxial flexure strength (BFS), diametral tensile strength (DTS), and compressive strength (CS). Hydroxyapatite (HAP; mass fraction of 40%), and micro-sized glass (mass fraction of 50%) composites as well as a commercial visible light curable base/liner were also tested. The significance between mean values was determined by Student–Newman–Keuls multiple comparisons ( p<0.05). Results. BFS of dry and wet (24 h at 37°C in water) ACP composites (60.3 and 62.0 MPa, respectively) were significantly lower than those of the comparison materials (79.2–109.3 MPa). CS values were likewise lower (62.9 MPa dry and 67.6 MPa wet vs 80.6–196.8 MPa) except for the wet base/liner (58.5 MPa). DTS of the dry ACP composite (21.8 MPa) was comparable with that of the HAP (22.8 MPa) and glass (25.5 MPa) composites, but lower than that of the base/liner (36.2 MPa). DTS decreased significantly when the ACP composite was wet (17.8 MPa). Significance. These results suggest that the remineralizing ACP polymeric composites, although mechanically weaker in some respects than other polymeric composites, have properties suitable for use as base and lining materials.

Dominant-negative effect on adhesion by myelin Po protein truncated in its cytoplasmic domain.

The myelin Po protein is believed to hold myelin together via interactions of both its extracellular and cytoplasmic domains. We have already shown that the extracellular domains of Po can interact in a homophilic manner (Filbin, M.T., F.S. Walsh, B.D. Trapp, J.A. Pizzey, and G.I. Tennekoon. 1990. Nature (Lond.). 344:871-872). In addition, we have shown that for this homophilic adhesion to take place, the cytoplasmic domain of Po must be intact and most likely interacting with the cytoskeleton; Po proteins truncated in their cytoplasmic domains are not adhesive (Wong, M.H., and M.T. Filbin, 1994. J. Cell Biol. 126:1089-1097). To determine if the presence of these truncated forms of Po could have an effect on the functioning of the full-length Po, we coexpressed both molecules in CHO cells. The adhesiveness of CHO cells expressing both full-length Po and truncated Po was then compared to cells expressing only full-length Po. In these coexpressors, both the full-length and the truncated Po proteins were glycosylated. They reached the surface of the cell in approximately equal amounts as shown by an ELISA and surface labeling, followed by immunoprecipitation. Furthermore, the amount of full-length Po at the cell surface was equivalent to other cell lines expressing only full-length Po that we had already shown to be adhesive. Therefore, there should be sufficient levels of full-length Po at the surface of these coexpressors to measure adhesion of Po. However, as assessed by an aggregation assay, the coexpressors were not adhesive. By 60 min they had not formed large aggregates and were indistinguishable from the control transfected cells not expressing Po. In contrast, in the same time, the cells expressing only the full-length Po had formed large aggregates. This indicates that the truncated forms of Po have a dominant-negative effect on the adhesiveness of the full-length Po. Furthermore, from cross-linking studies, full-length Po, when expressed alone but not when coexpressed with truncated Po, appears to cluster in the membrane. We suggest that truncated Po exerts its dominant-negative effect by preventing clustering of full-length Po. We also show that colchicine, which disrupts microtubules, prevents adhesion of cells expressing only the full-length Po. This strengthens our suggestion that an interaction of Po with the cytoskeleton, either directly or indirectly, is required for adhesion to take place.

Respiratory responses of the salt marsh animals, Fundulus heteroclitus, Leiostomus xanthurus, and Palaemonetes pugio to environmental hypoxia and hypercapnia and to the organophosphate pesticide, azinphosmethyl

In tidal saltmarshes in South Carolina hypoxic (low O 2) and hypercapnic (high CO 2) conditions occur frequently. In the summer, water Po 2 was measured in the upper marshes and over a 24-h period ranged from 9 to 170 torr and Pco 2 ranged from 0.3 to 12 torr. These conditions depend on the stage of the tide and the time of day. The respiratory responses to different levels of Po 2 and Pco 2 of the grass shrimp, Palaemonetes pugio, the spot fish, Leiostomus xanthurus, and the killifish or mummichog, Fundulus heteroclitus living and feeding in the saltmarsh were investigated. Mean oxygen uptake in P. pugio, L. xanthurus, and F. heteroclitus at normoxic Po 2 (130–150 torr) and low Pco 2 (< 0.6 torr) was 17.5, 17.1, and 9.5 μmol · g −1 · h −1 and 16.3, 24.5, and 10.5 μmol · g −1 · h −1 at high Pco 2 (= 7 torr), respectively. The critical Po 2 for all species was between 30 and 35 torr. Mean whole body lactate concentrations in P. pugio, L. xanthurus, and F. heteroclitus at Pco 2 < 0.6 torr are 3.5, 2.4, and 2.3 μmol · g −1, respectively, in normoxia and 12.3, 4.5, and 11.0 μmol · g −1 ( p < 0.05; Dunn's pairwise test) in hypoxia and Pco 2 < 0.6 torr. In these saltmarsh animals there appears in general to be no specific effects on oxygen uptake of environmental fluctuations in CO 2 over a wide range of Po 2. The organophosphate pesticide, azinphosmethyl, appears to have no effect on the oxygen uptake of these three species at concentrations of 10 μg · l −1 for fish and 2 μg · l −1 for shrimp.

The effects of gossypol and chloroquine interaction on serum electrolytes of protein-malnourished rats

Serum sodium (Na), potassium (K), chloride (Cl), phosphate (Po), and calcium (Ca) were assayed in adult male Wistar rats fed a low protein diet (LP) and a normal protein diet (control, NP) and administered gossypol (GP) and chloroquine (CQ) alone and in combination (GPCQ), for 4 and 8 weeks. Gossypol was administered at 20 mg/kg body wt/rat/day in Goya oil and chloroquine at 5 mg/kg body wt/rat for 3 days/week in distilled water. The data, analyzed by two-way ANOVA, showed that the interaction had significant effects on the serum levels of Na, K, and Po (P<0.001) but not on chloride and calcium (P>0.05). Serum levels of sodium, potassium and phosphate in LP rats were significantly lower than in NP rats. In LP and NP rats, the levels of Na, K, and Po at 8 weeks were significantly higher than at 4 weeks; and GPCQ treatment produced significantly lower sodium levels in LP and NP rats, lower phosphate in LP rats and higher phosphate in NP-fed rats than GP or CQ administered alone. Potassium level in GPCQ was between levels in Gp- and CQ-treated rats. The administration of gossypol and chloroquine together may not adversely affect serum electrolytes in protein-malnutrition state any more than gossypol or chloroquine administered alone.

Effect of tillage and fertilization on inorganic and organic soil phosphorus

This study was conducted to evaluate the impact of tillage and fertilization practices on soil organic carbon (organic-C) and the distribution of phosphorus between inorganic (Pi) and organic (Po) pools in a clay and sandy loam soil under a continuous corn (Zea mays L.) production system. Tillage treatments were established in the fall of 1981. The soils for this study were sampled (0- to 10-cm and 10- to 20-cm) in June 1988. Treatments consisted of three types of tillage: (i) conventional (CT): fall moldboard ploughing with two spring diskings; (ii) reduced (RT): with either fall chisel ploughing (1981–1986) or no fall tillage (1987) followed by one spring disking, and (iii) no-till (NT); and two types of fertilization (i) inorganic (I): 170 kg N ha−1. 80 kg P2O5, ha−1, 75 kg K2O ha−1, and (ii) organic fertilizer (O): dairy manure applied to give 170 kg N ha−1 plus 80 kg P2O5, ha−1 from inorganic P fertilizer. Even though a lime application was made in the fall of 1985, soil pH was significantly lower in the I fertilizer treatments. Reduction of tillage intensity resulted in a lower pH in the surface layer of the sandy loam soil. Tillage did not affect soil organic-C, or total soil Po (soil-Po) in either soil. Compared with the I fertilizer treatment, the O fertilizer treatment resulted in increased levels of soil organic-C and soil-Po only in the sandy loam soil. Labile levels of Po in the soil were not affected by treatments. Increased soil-Po levels possibly resulted from an increase in stable Po complexes. Moderately labile Po levels were not affected by treatments in the clay soil. In the sandy loam soil, O fertilization decreased moderately labile Po levels in the surface layer of the NT treatment, and increased this P fraction in the 10- to 20-cm soil layer of the RT and CT treatments. In the surface layer of both soils, labile levels of Pi were greater for the O fertilization treatment (approximately 40 and 47% higher for the clay and sandy loam, respectively), and were lower under CT. Increased labile Pi levels were associated with the O fertilizer treatment in the 10- to 20-cm depth increment in the sandy loam soil only, suggesting a greater downward movement of P with manure applications. Key words: Conventional tillage, zero-tilled, no-till, reduced tillage, manure, P fractionation