Adverse effects of tempol on hidrosaline balance in rats with acute sodium overload

We studied the effects of tempol, an oxygen radical scavenger, on hydrosaline balance in rats with acute sodium overload. Male rats with free access to water were injected with isotonic (control group) or hypertonic saline solution (0.80 mol/l NaCl) either alone (Na group) or with tempol (Na-T group). Hydrosaline balance was determined during a 90 min experimental period. Protein expressions of aquaporin 1 (AQP1), aquaporin 2 (AQP2), angiotensin II (Ang II) and endothelial nitric oxide synthase (eNOS) were measured in renal tissue. Water intake, creatinine clearance, diuresis and natriuresis increased in the Na group. Under conditions of sodium overload, tempol increased plasma sodium and protein levels and increased diuresis, natriuresis and sodium excretion. Tempol also decreased water intake without affecting creatinine clearance. AQP1 and eNOS were increased and Ang II decreased in the renal cortex of the Na group, whereas AQP2 was increased in the renal medulla. Nonglycosylated AQP1 and eNOS were increased further in the renal cortex of the Na-T group, whereas AQP2 was decreased in the renal medulla and was localized mainly in the cell membrane. Moreover, p47-phox immunostaining was increased in the hypothalamus of Na group, and this increase was prevented by tempol. Our findings suggest that tempol causes hypernatremia after acute sodium overload by inhibiting the thirst mechanism and facilitating diuresis, despite increasing renal eNOS expression and natriuresis.     

Differential effect of dexamethasone on the regulation of phospholipase A2 and prostanoid synthesis in undifferentiated and phorbolester-differentiated U937 cells

The human undifferentiated histiocytic cell-line U937 can be induced to differentiate by incubation with 12-0-tetradecanoylphorbol-13-acetate (TPA) into macrophage-like cells. Dexamethasone reduced the prostaglandin production in TPA-differentiated U937 cells dose dependently, whereas undifferentiated U937 cells were dexamethasone insensitive. Concomitantly phospholipase A2, the enzyme liberating the prostaglandin precursor arachidonic acid, was inhibited by dexamethasone in TPA-differentiated but not in undifferentiated U937 cells. The activity of lysophosphatide acyltransferase, the key enzyme of fatty acid reacylation into phospholipids, remained unchanged both in undifferentiated and TPA-differentiated U937 cells. The data suggest that responsiveness to glucocorticoid-dependent regulation of prostanoid synthesis is acquired by cells of the monocyte-macrophage lineage late in differentiation.     

Control of prostanoid synthesis: role of reincorporation of released precursor fatty acids

Prostanoid synthesis is limited by the availability of free arachidonic acid. This polyunsaturated fatty acid is liberated by phospholipases and usually is an intermediate of the deacylation-reacylation cycle of membrane phospholipids. In rat peritoneal macrophages, ethylmercurisalicylate (merthiolate) or N-ethylmaleimide (NEM) dose dependently inhibited the incorporation of arachidonic acid into cellular phospholipids, at lower concentrations specifically into phosphatidylcholine. Furthermore, merthiolate could be shown to be a rather selective inhibitor of lysophosphatidylcholine acyltransferase. In contrast, phospholipase A2 activity was not affected over a wide dose range. Consequently, macrophages showed a large increase in prostanoid synthesis (prostaglandin E, prostacyclin and thromboxane) in the presence of both lysophosphatide acyltransferase inhibiting agents. Similar results were obtained with human platelets, in which merthiolate increased the release of thromboxane. Addition of free arachidonic acid also enhanced prostanoid synthesis in macrophages. At optimal concentrations, merthiolate had no further augmenting effect. It is concluded that the rate of prostanoid synthesis is not only controlled by phospholipase A2 activity, but rather by the activity of the reacylating enzymes, mainly lysophosphatide acyltransferase.     

Cell cycle-specific changes in β-adrenergic receptor concentrations in C6 glioma cells

The concentration of β-adrenergic receptors in synchronized C6 cells is lowest during mitosis and G₁ (1000–2000 receptors/cell). A rapid increase in β-receptor concentration occurs in early S phase to 9000 receptors/cell, followed by a decrease during G₂ to the low concentration found at mitosis. In non-synchronized C6 cell populations, mitotic cells have one-half of the average β-receptor concentration of the population as a whole, confirming the observations made with synchronized cells.     

Beiträge zur Cytologie des Xylems

Zusammenfassung Die vorliegenden Untersuchungen sind Einzelbeobachtungen an Xylemzellen vonVicia faba undCucurbita Pepo. Sie sollen auf die besonderen entwicklungsgeschichtlichen Verhältnisse aufmerksam machen, die bei der Tracheen- und Tracheidendifferenzierung vorliegen. Es ist anzunehmen, daß die an die Wasserleitungsgefäße direkt angrenzenden lebenden Holzparenchymzellen, hier Begleitzellen genannt, eine bedeutende Rolle bei der Differenzierung der Gefäßwandung spielen. Der geschlossene Holzparenchymmantel, der die Gefäße umgibt, ist außerdem Voraussetzung für die Erhaltung eines kontinuierlichen Wasserfadens und Aufrechterhaltung der Saugspannung in den Tracheen. Man kann daher von einer entwicklungsgeschichtlichen und physiologischen Einheit zwischen den Gefäßen und ihren Begleitzellen sprechen. So betrachtet, stellen die Xylem-Begleitzellen eine Parallele zu den Geleitzellen der Siebröhren dar, die mit diesen ebenfalls eine Funktionseinheit darstellen.Mit 12 Textabbildungen     

Effects of central alpha-MSH injections on performance in a cued discrimination task.

Alpha-MSH has been implicated in changing attention behavior following peripheral injections, but no brain sites were studied. In the present report, alpha-MSH was injected directly into specific sites in the medial anterior hypothalamic/preoptic area (MAHPOA) while measuring performance in a visually cued discrimination task. Alpha-MSH injections resulted in reduced errors, indicated by decreased responding during noncued intervals, but no change in responding to correct cues. The improved error rate was consistent with attentional changes in a variety of paradigms. Attentional and motivational parameters were differentiated. The injected alpha-MSH appears to act on an inhibitory component of an attentional mechanism.     

Three-dimensional numerical analysis of pulsatile flow and wall shear stress in the carotid artery bifurcation.

To analyse the pulsatile flow field and the mechanical stresses in a three-dimensional carotid artery bifurcation model, computer simulation is applied. The approximation of the Navier-Stokes equations uses a pressure correction finite element method. Numerical results are presented for axial and secondary flow velocity and wall shear stresses with special emphasis on the fluid dynamics in the carotid sinus. This region is of major interest because it is affected preferentially by lesions. Detailed local flow studies as carried out here should lead to a further insight into the mechanisms of atherogenesis. The flow conditions used in the study were chosen according to Ku et al. (Arteriosclerosis 5, 293-302, 1985). The results of this numerical analysis agree in the essential features with their experimental results.     

Pertussis toxin B-subunit-induced Ca2(+)-fluxes in Jurkat human lymphoma cells: the action of long-term pre-treatment with cholera and pertussis holotoxins

The exotoxins of Bordetella pertussis and Vibrio cholera have been used to investigate signal transduction in the human T-cell lymphoma Jurkat. Stimulation of the cells, leading to an increase in cytoplasmic free calcium, could be achieved by the anti-T-cell receptor complex antibody OKT3 and by pertussis holotoxin (PTHT), or its B-subunit (PTB), but not by cholera holotoxin (CTHT) or its B-subunit (CTB). Both holotoxins ADP-ribosylated specifically G-proteins in the plasma membrane of intact cells, while their B-subunits had no ADP-ribosyltransferase activity. Incubation of the cells with CTHT led to a state of unresponsiveness to all stimulants. CTB was without any effect, indicating that the ADP-ribosyltransferase activity of cholera toxin (located in the A-subunit of the holotoxin) was necessary for the inhibition of cellular signalling. The inhibitory effect of cholera toxin on the pertussis toxin action was not due to a blockade of pertussis toxin interaction with the cell surface, because pertussis toxin was still able to ADP-ribosylate membrane proteins in cholera toxin treated intact cells. In addition, the cholera toxin mediated inhibition was not due to elevated levels of cyclic-AMP, as forskolin (a direct activator of the adenylate cyclase) and no inhibitory effect. The stimulating effect of PTHT was independent of its ADP-ribosyltransferase activity, because it could also be obtained by the B-subunit alone. In addition, the increase of cytoplasmic free calcium after stimulation by PTHT clearly preceded the ADP-ribosylation. Pre-treatment with PTHT, PTB or OKT3, led to a long lasting increase in the level of intracellular Ca2+ in Jurkat cells, which could not, therefore, be stimulated further. Inhibition by cholera holotoxin of the stimulation by OKT3 and pertussis toxin (PTHT and PTB) imply that the mitogenic effect of pertussis toxin is perhaps mediated via the T-cell antigen receptor signalling cascade. The presented data do not support the idea that a pertussis toxin-sensitive G-protein is involved in coupling the T-cell antigen receptor to the phospholipase C.     

Sporogenesis in Eusporangiate Ferns: I. Monoplastidic Meiosis in Angiopteris (Marattiales)

Angiopteris (Marattiales) undergoes the more primitive form of monoplastidic meiosis, while other ferns have evolved the polyplastidic type typical of seed plants. In monoplastidic cell division, the single plastid divides and serves as site of the microtubule organizing center (MTOC) for spindle formation resulting in coordinated division of plastid, nucleus, and cytoplasm. In plants with polyplastidic cell division, the MTOC is diffuse and generally perinuclear. Monoplastidic cell division is seen as a plesiomorphic feature that was inherited from algal ancestors containing a single plastid and modified through evolution. Monoplastidic meiosis occurs in all groups of bryophytes (although in only a few hepatics), Isoetes, Selaginella, certain generic segregates of Lycopodium, and in members of the Marattiales. It is not known to occur in psilophytes, Equisetum, leptosporangiate ferns, or seed plants. Received 30 January 2001/ Accepted in revised form 24 April 2001     

Interleukin 1 and the glomerular mesangium. I. Purification and characterization of a mesangial cell-derived autogrowth factor

The proteins expressing interleukin 1 (IL 1) activity from rat peritoneal macrophages and cultured glomerular mesangial cells were compared after purification to apparent homogeneity. The purified IL 1 shared a number of biochemical features including m.w., charge, and specific activity. These findings were extended by the results of proteolytic peptide mapping, which revealed similar breakdown oligopeptides, confirming the close resemblance of these two IL 1 species produced by macrophages and mesangial cells. The purified mesangial cell IL 1 acts as an autocrine or paracrine growth factor. The local release of this cytokine may be an important factor in glomerular diseases characterized by mesangial proliferation and matrix expansion.