Therapeutic effect of tirilazad mesylate (U-74006F), mannitol, and their combination on experimental ischemia

The effect of tirilazad mesylate (U-74006F), mannitol, and their combination was investigated on focal cerebral ischemia induced by permanent middle cerebral artery (MCA) occlusion in rabbits. Rabbits were divided into four groups receiving vehicle, U-74006F, mannitol, and U-74006F plus mannitol. Hematocrit (hct), glucose, mean arterial blood pressure (MABP), pH, PCO2, and PO2 were measured both before and after occlusion. Seventy-two hours following the permanent MCA occlusion, the neurological outcome was assessed and a quantitative neuropathologic examination was performed in all rabbits. The neurological outcome was better in the rabbits treated with U-74006F plus mannitol than in the other groups. The size of infarction of the affected hemisphere following MCA occlusion was 49.7% in the control group, 30.6% in the U-74006F group, 47.6% in the mannitol group, and 24.1% in the U-74006F plus mannitol group. There was a statistically significant reduction in infarct size in the U-74006F plus mannitol group compared with the other groups (P < 0.05). The ratio of ischemic neurons to total neurons in the cortex was smaller in the U-74006F plus mannitol group than in the other groups. The ratio of ischemic neurons to total neurons in the subcortex was significantly lower in the U-74006F plus mannitol group than in the other groups (P < 0.05). Our data provide evidence for the beneficial effects of both U-74006F and U-74006F plus mannitol in promoting neurological recovery and preservation of the ischemic area.

Regulation of the urine concentration mechanism by the oropharyngeal afferent pathway in man

BACKGROUND

It has been reported that the oropharyngeal afferent pathway behaves as a first-order factor regulating body fluid. However, the neural mechanism has not yet been clear. This study was designed to elucidate the characteristics of the neural mechanism in man.

METHODS

Healthy human subjects kept either an isotonic or hypertonic solution in the oral cavity so as to moisten the oropharyngeal mucosa without intake for 20 min. Plasma vasopressin (AVP) concentration, urine volume and urine and plasma osmolalities were measured before and after the application.

RESULTS

The oropharyngeal application of isotonic saline induced no significant changes in plasma AVP concentration, urine volume and osmolality, while that of hypertonic saline induced a significant decrease and increase in urine volume and osmolality, respectively. The plasma AVP concentration increased significantly after the application of hypertonic saline. Mannitol also induced a significant decrease and increase in urine volume and osmolality, respectively. However, the urinary responses after the application of mannitol were delayed compared with those of hypertonic saline. There were no significant changes in plasma osmolality before and after each application.

CONCLUSION

These results suggest that the oropharyngeal afferent pathway from the oropharynx to hypothalamic AVP-producing cells takes part in the thirst mechanism regulating body fluid in humans. The oropharyngeal afferent signals may behave as sodium-chloride-sensitive osmoreceptor.

Modulation of CFTR gene expression in HT-29 cells by extracellular hyperosmolarity

Hypertonicity has pleiotropic effects on cell function, including activation of transporters and regulation of gene expression. It is important to investigate the action of hypertonicity on cystic fibrosis gene expression because cystic fibrosis transmembrane conductance regulator (CFTR), the cAMP-regulated Cl(-) channel, regulates ion transport across the secretory epithelia, which are often in a hypertonic environment. We found that adding >150 mosmol/l NaCl, urea, or mannitol to the culture medium reduced the amount of CFTR mRNA in colon-derived HT-29 cells in a time-dependent manner. Studies with inhibitors of various kinases [H-89 (protein kinase A inhibitor), bisindolylmaleimide (protein kinase C inhibitor), staurosporine (serine/threonine kinase inhibitor) and herbimycin A (tyrosine kinase inhibitor), SB-203580 and PD-098059 (mitogen-activated protein kinase inhibitors)] showed that CFTR gene expression and its decrease by added NaCl required p38 kinase cascade activity. The CFTR gene activity is regulated at the transcriptional level, since adding NaCl diminished the luciferase activity of HeLa cells transiently transfected with the CFTR promoter. This regulation requires protein synthesis. The complexity of the reactions involved in blocking CFTR gene transcription by NaCl strongly suggests that the decrease in CFTR mRNA is part of a general cell response to hyperosmolar stress.

Taurine prevents high-glucose-induced human vascular endothelial cell apoptosis

Elevated blood glucose in uncontrolled diabetes is causally correlated with diabetic microangiopathy. Hyperglycemia-triggered accelerated endothelial cell apoptosis is a critical event in the process of diabetes-associated microvascular disease. The conditionally semiessential amino acid taurine has been previously shown to protect against human endothelial cell apoptosis. Therefore, this study was designed to investigate the role of taurine in the prevention of high-glucose-mediated cell apoptosis in human umbilical vein endothelial cells (HUVEC) and the mechanisms involved. Exposure of HUVEC to 30 mM glucose for 48 h (short-term) and 14 days (long-term) resulted in a significant increase in apoptosis, compared with normal glucose (5.5 mM; P < 0.05). High-glucose-induced DNA fragmentation preferentially occurred in the S phase cells. Mannitol (as osmotic control) at 30 mM failed to induce HUVEC apoptosis. Taurine prevented high-glucose-induced HUVEC apoptosis, which correlates with taurine attenuation of high-glucose-mediated increased intracellular reactive oxygen species (ROS) formation and elevated intracellular Ca(2+) concentration ([Ca(2+)](i)) level. Antioxidants, DMSO, N-acetyl cysteine, and glutathione, only partly attenuated high-glucose-induced HUVEC apoptosis. Glucose at 30 mM did not cause HUVEC necrosis. However, both glucose and mannitol at 60 mM caused HUVEC necrosis as represented by increased lactate dehydrogenase release and cell lysis. Taurine failed to prevent hyperosmolarity-induced cell necrosis. These results demonstrate that taurine attenuates hyperglycemia-induced HUVEC apoptosis through ROS inhibition and [Ca(2+)](i) stabilization and suggest that taurine may exert a beneficial effect in preventing diabetes-associated microangiopathy.

Hyperosmolar D-mannitol reverses the increased membrane excitability and the nodal swelling caused by Caribbean ciguatoxin-1 in single frog myelinated axons

The effects of hyperosmolar D-mannitol were studied on single frog myelinated nerve fibres previously poisoned with Caribbean ciguatoxin-1 (C-CTX-1), a new toxin isolated from the pelagic fish Caranx latus inhabiting the Caribbean region. In current-clamped myelinated axons, C-CTX-1 (50-120 nM) caused spontaneous and repetitive action potential discharges after a short delay. In addition, the toxin produced a marked swelling of nodes of Ranvier of myelinated axons that reached a steady state within about 90 min, as revealed by using confocal laser scanning microscopy. The increased excitability and the nodal swelling caused by C-CTX-1 were prevented or reversed by an external hyperosmotic solution containing 100 mM D-mannitol. Moreover, the C-CTX-1-induced nodal swelling was completely prevented by the blockade of voltage-sensitive sodium channels by tetrodotoxin (TTX). It is suggested that C-CTX-1, by increasing nerve membrane excitability, enhances Na(+) entry into nodes of Ranvier through TTX-sensitive sodium channels, which directly or indirectly disturb the osmotic equilibrium between intra- and extra-axonal media resulting in an influx of water that was responsible for the long-lasting nodal swelling. The fact, that hyperosmolar D-mannitol either reversed or prevented the neurocellular actions of C-CTX-1, is of particular interest since it provides the rational basis for its use to treat the neurological symptoms of ciguatera fish poisoning in the Caribbean area.

Marked increase of guanylin secretion in response to salt loading in the rat small intestine

Guanylin and uroguanylin are intestinal peptides that stimulate guanylate cyclase C and cause chloride secretion. These peptides show topological instability due to two disulfide bonds. The disulfide bonds were reduced and S-carboxymethylated to cleave the bonds and obtain stable and sole derivatives. We established a new and reliable RIA system for the stable derivatives from both peptides. With the use of this system, the response of the peptides to salt loading of the rat small intestine was evaluated. The lumen of the small intestines of Sprague-Dawley rats was perfused in vivo with Krebs-Ringer solution containing different concentrations of salt or mannitol. Mature guanylin, proguanylin, and mature uroguanylin were found in the perfusate in the basal state. The highest salt loading (200 mM NaCl for 20 min) increased the guanylin secretion about threefold (1.9 +/- 0.2 vs. 5.4 +/- 0.5 pmol/min), with the effect lasting for 60 min. The uroguanylin secretion was less affected. Hyperosmolar mannitol also caused a significant but smaller increase of guanylin secretion. Increased guanylin could lead to increased salt and water secretion of the intestine; thus members of the guanylin family have potential roles in the regulation of water and salt metabolism in the small intestine.

Effects of mannitol or catalase on the generation of reactive oxygen species leading to DNA damage by Chromium(VI) reduction with ascorbate

Interaction of Cr(VI) and ascorbate in vitro generates Cr(V), Cr(IV), Cr(III), carbon-based alkyl radicals, COO(*)(-), (*)OH, and ascorbate radicals and induces DNA interstrand cross-links at guanines. To determine which specific Cr species and free radicals cause DNA damage, we investigated the effects of mannitol and catalase on the formation of reactive intermediates, Cr-DNA associations, DNA polymerase-stop sites, and 8-hydroxydeoxyguanosine (8-OHdG) adducts induced by Cr(VI)/ascorbate in a Hepes buffer. EPR spectra showed that mannitol trapped reactive Cr(V), forming a stable Cr(V)-diol complex, and inhibited the radicals induced by Cr(VI)/ascorbate, whereas catalase or heat-denatured catalase enhanced the levels of Cr(V) without altering the radical signals. Mannitol markedly inhibited the retarded gel electrophoretic mobility of supercoiled plasmids and the formation of DNA polymerase-stop sites induced by Cr(VI)/ascorbate, but catalase did not. On the other hand, mannitol reduced only 32% of the Cr-DNA adducts induced by Cr(VI)/ascorbate, suggesting that Cr monoadducts (possibly DNA-Cr-mannitol adducts) are the major lesions generated in the Cr(VI)/ascorbate/mannitol/DNA solution. Native catalase but not heat-denatured catalase protected approximately 25% of the Cr-DNA adducts induced by Cr(VI)/ascorbate, suggesting that hydrogen peroxide may be involved. Mannitol could not completely inhibit the formation of 8-OHdG adducts induced by Cr(VI)/ascorbate, indicating that this DNA damage may be generated before the action of mannitol to trap Cr(V) and reactive oxygen species. Alternatively, Cr-peroxide intermediates may also lead to 8-OHdG formation to account for the incomplete prevention by mannitol. Catalase or heat-denatured catalase partially protected the formation of 8-OHdG adducts induced by Cr(VI)/ascorbate, suggesting an effect of proteins. Together, the results from this study suggest that the primary species generated during the reduction of Cr(VI) by ascorbate are hydroxyl radicals and Cr(V) species, responsible for the formation of 8-OHdG and DNA cross-links, respectively.

Effects of mannitol and dimethylthiourea on helicobacter pylori-induced IL-8 production in gastric epithelial cells

The present study aims at investigating the effects of mannitol and dimethylthiourea, known hydroxyl radical scavengers, on lipid peroxidation as an indicative of oxidative damage, NF-kappa B activation and IL-8 production by Helicobacter pylori in gastric epithelial cells. A human gastric epithelial cell line, AGS, treated with or without mannitol and dimethylthiourea, was incubated in the absence or the presence of H. pylori. As a result, H. pylori significantly stimulated the productions of lipid peroxide and IL-8. Treatment with H. pylori resulted in the activation of two species of NF-kappa B dimers (a p50/p65 heterodimer and a p50 homodimer). Mannitol and dimethylthiourea significantly inhibited lipid peroxide production, NF-kappa B complex formation and IL-8 production by H. pylori. In conclusion, mannitol and dimethylthiourea may attenuate H. pylori-induced gastric inflammation by inhibiting lipid peroxidation and NF-kappa B activation and thereby decreasing IL-8 production.

[Mathematical coupling and "regression to the mean". A statistical case history]

"Regression to the mean" (RTM) is a statistical phenomenon originating from the random variation of variables rather than a true association between the variables. RTM is closely linked to mathematical coupling; unawareness of these phenomena may lead to misinterpretation of data. A study examining intracranial pressure before and after infusion of manitol is presented, in which mathematical coupling caused a highly significant (but spurious) correlation between the analysed data. The significance of RTM and mathematical coupling is demonstrated by analysis of a data set derived from random numbers.

Iodinated radiographic contrast media inhibit shear stress- and agonist-evoked release of NO by the endothelium

1 We have used isolated arterial preparations from the rabbit and dog to investigate whether non-ionic iodinated radiographic contrast media (IRCM) modulate nitric oxide (NO) release. The tri-iodinated monomers iopromide and iohexol were compared with the hexa-iodinated dimer iodixanol. 2 The vasodilator effects of iohexol (300 mg ml-1) and iodixanol (320 mg ml-1) were assessed in cascade bioassay. Increasing concentrations of iohexol or iodixanol caused concentration-dependent relaxations of the detector tissue which were insensitive to 100 microM NG-nitro L-arginine methyl ester (L-NAME) and 10 microM indomethacin, whereas viscosity-associated relaxations induced by the 'inert' agent dextran (MW 80,000; 1-4%) were attenuated by inhibition of NO synthesis. 3 Relaxations of endothelium-intact rings to acetylcholine (ACh) were attenuated by preincubation with iohexol or iodixanol, whereas relaxations to sodium nitroprusside (SNP) in endothelium-denuded rings were unaffected. Inhibitory activity did not correlate with either molarity or iodine concentration. Mannitol caused inhibition of both ACh- and SNP-induced responses. 4 In isolated perfused arteries the depressor responses to iodixanol (320 mg ml-1) and iopromide (300 mg ml-1) administered as close arterial bolus attained a plateau with maximal dilatations of approximately 25% and approximately 60%, respectively. Addition of 100 microM NG-nitro L-arginine (L-NOARG) and/or 10 microM indomethacin to the perfusate had no effect on the responses to either agent. 5 We conclude that IRCM exert direct effects on the endothelium that inhibit NO production rather than its action on vascular smooth muscle. Shear stress-induced stimulation of NO production by IRCM is unlikely to contribute to their vasodilator activity in vivo when administered during angiography despite high intrinsic viscosity.

Posttreatment with the immunosuppressant cyclosporin A in transient focal ischemia

Cyclosporin A (CsA) reduces ischemic brain damage when administered in such a way that its penetration across the blood-brain barrier is enhanced. Since only pretreatment has previously been used in focal ischemia, the objective of the present study was to establish whether posttreatment is efficacious and to assess the window of therapeutic opportunity for CsA. To that end, CsA was given 5 min to 6 h after the start of reperfusion following 2 h transient ischemia, and infarct volume was assessed after 48 h by triphenyltetrazolium chloride staining. Attempts were made to circumvent the BBB to CsA by an intracerebral needle lesion, by an increase in the intravenous CsA dose, or by osmotic opening with intracarotid mannitol. The results were compared to those obtained with FK506. Intravenous CsA in a dose of 10 mg/kg failed to reduce infarct volume, unless preceded by a needle lesion. That procedure, and an increase in CsA dose to 50 mg/kg, reduced infarct volume to about 50% of control, but the higher dose had toxic side effects. The coupled intracarotid infusion of mannitol and CsA (10 mg/kg) was more efficacious, without overt side effects. However, mannitol proved dispensable since CsA alone reduced infarct volume to 30% of control, with a therapeutic window of 3-6 h. When given after 5 min of reflow, CsA reduced infarct volume to 10% of control and was clearly more neuroprotective than FK506. Possibly, this is because CsA blocks the mitochondrial permeability transition pore which is opened under adverse conditions.

Three actin cross-linking proteins, the 34 kDa actin-bundling protein, alpha-actinin and gelation factor (ABP-120), have both unique and redundant roles in the growth and development of Dictyostelium

The contribution of three actin cross-linking proteins, alpha-actinin (alphaA), gelation factor (ABP-120), and the 34 kDa actin-bundling protein to cellular functions has been studied in three single mutant (alphaA-, 120-, and 34-) and three double mutant (alphaA-/120-, 34-/alphaA-, 34-/120-) strains of Dictyostelium generated by homologous recombination. Strains alphaA-/120- and 34-/alphaA- exhibited a reduced rate of pinocytosis, grew to lower saturation densities, and produced small cells in shaking cultures. All strains grew normally in bacterial suspensions and on agar plates with a bacterial lawn. Slow growth under conditions of reduced temperature and increased osmolarity was observed in single mutants 34- and alphaA-, respectively, as well as in some of the double mutant strains. Motility, chemotaxis, and development were largely unaltered in 34-/alphaA- and 34-/120- cells. However, 34-/alphaA- cells showed enhanced aggregation when starved in suspension. Moreover, morphogenesis was impaired in both double mutant strains and fruiting bodies of aberrant morphology were observed. These defects were reverted by re-expression of one of the lacking cross-linking proteins. The additive and synthetic phenotypes of these mutations indicate that actin cross-linking proteins serve both unique and overlapping functions in the actin cytoskeleton.

ERK activation by urea in the renal inner medullary mIMCD3 cell line

Urea- and NaCl-inducible extracellular signal-regulated kinase (ERK) phosphorylation exhibited dissimilar kinetics. Among cell lines examined, the effect of urea was unique to mIMCD3 inner medullary collecting duct cells and MDCK cells. Urea-inducible ERK activation was approximately 10-fold less sensitive to the MEK inhibitor, PD-98059, than was that of NaCl. This difference did not appear to be accounted for by differential activation of MEK isoforms. Interestingly, the inhibitor of p38 activation, SB-203580, abrogated the effect of both urea and NaCl upon both ERK and MEK activation; however, the former was much less sensitive to the inhibitor. Consistent with this observation, NaCl was much more effective than urea at inducing p38 phosphorylation. The effect of hypertonic stress (e.g., sorbitol 100 mM) could be blocked by appropriate medium dilution such that isotonicity was maintained. In marked contrast, the effect of hyperosmotic urea could not be blocked in this fashion, implying the absence of dependence upon cell volume. Together, these data suggest that cells of the renal inner medulla are potentially uniquely responsive to urea and that urea and hypertonic stressors induce ERK activation through distinct mechanisms.

Urea induces macrophage proliferation by inhibition of inducible nitric oxide synthesis

BACKGROUND

Atherosclerosis is a major cause of morbidity and mortality in chronic renal failure and is associated with the proliferation of macrophages within atherosclerotic lesions.

METHODS

Because the progression of atherosclerosis as a consequence of decreased nitric oxide synthesis has been described, we investigated the correlation between the inhibition of inducible nitric oxide synthase (iNOS) by urea, macrophage proliferation as assayed by cell counting, tritiated thymidine incorporation and measurement of cell protein, and macrophage apoptosis.

RESULTS

Urea induces a dose-dependent inhibition of inducible nitric oxide synthesis in lipopolysaccharide-stimulated mouse macrophages (RAW 264.7) with concomitant macrophage proliferation. Macrophage proliferation, as determined by cell counting, became statistically significant at 60 mM urea, corresponding to a blood urea nitrogen level of 180 mg/100 ml, concentrations seen in uremic patients. iNOS protein expression showed a dose-dependent reduction, as revealed by immunoblotting when cells were incubated with increasing amounts of urea. The decrease of cytosolic DNA fragments in stimulated macrophages incubated with urea shows that the proliferative actions of urea are associated with a decrease of NO-induced apoptosis.

CONCLUSIONS

Our data demonstrate that the inhibition of iNOS-dependent NO production caused by urea enhances macrophage proliferation as a consequence of diminished NO-mediated apoptosis.

Iron-dependent human platelet activation and hydroxyl radical formation: involvement of protein kinase C

BACKGROUND

Iron is an important modulator of lipid peroxidation, and its levels have been associated with the progression of atherosclerosis. Little is known about the possibility that this metal, when released from tissue stores, may modulate the reactivity of blood cell components, in particular platelets. Therefore, we investigated a possible link between iron, oxygen free radical formation, and platelet function.

METHODS AND RESULTS

Human whole blood was stimulated with collagen 2 micrograms/mL, and an irreversible aggregation with thromboxane (Tx)B2 formation was observed (15+/-4 versus 130+/-10 ng/mL). Deferoxamine (DSF), a specific iron chelator, and catalase, an H2O2 scavenger, inhibited collagen-induced whole-blood aggregation. The aggregation was accompanied by an increase in hydroxyl radical (OH.) levels (30+/-8 versus 205+/-20 nmol/L dihydroxybenzoates), which were reduced by DSF and by 2 specific OH. scavengers, mannitol and deoxyribose. Iron (Fe2+) dose-dependently induced platelet aggregation, TxB2 formation (6+/-2 versus 135+/-8 ng/mL), and protein kinase C (PKC) translocation from the cytosol to the cell membrane when added to platelets that have been primed with a low concentration of collagen (0.2 micrograms/mL). In the same system, an increase in OH. levels was observed (37+/-12 versus 230+/-20 nmol/L dihydroxybenzoates). Mannitol and deoxyribose, but not urea, were able to reduce OH. formation, PKC activation, and platelet aggregation. Selective inhibition of PKC activity by GF 109203X prevented iron-dependent platelet aggregation without influencing OH. production.

CONCLUSIONS

The present study shows that iron can directly interact with human platelets, resulting in their activation. Its action is mediated by OH. formation and involves PKC activity. Our findings provide an additional contribution to the understanding of the mechanism(s) by which iron overload might promote atherosclerosis and coronary artery disease.

Partially folded intermediates during trypsinogen denaturation

The equilibrium unfolding of bovine trypsinogen was studied by circular dichroism, differential spectra and size exclusion HPLC. The change in free energy of denaturation was delta GH2O = 6.99 +/- 1.40 kcal/mol for guanidine hydrochloride and delta GH2O = 6.37 +/- 0.57 kcal/mol for urea. Satisfactory fits of equilibrium unfolding transitions required a three-state model involving an intermediate in addition to the native and unfolded forms. Size exclusion HPLC allowed the detection of an intermediate population of trypsinogen whose Stokes radii varied from 24.1 +/- 0.4 A to 26.0 +/- 0.3 A for 1.5 M and 2.5 M guanidine hydrochloride, respectively. During urea denaturation, the range of Stokes radii varied from 23.9 +/- 0.3 A to 25.7 +/- 0.6 A for 4.0 M and 6.0 M urea, respectively. Maximal intrinsic fluorescence was observed at about 3.8 M urea with 8-aniline-1-naphthalene sulfonate (ANS) binding. These experimental data indicate that the unfolding of bovine trypsinogen is not a simple transition and suggest that the equilibrium intermediate population comprises one intermediate that may be characterized as a molten globule. To obtain further insight by studying intermediates representing different stages of unfolding, we hope to gain a better understanding of the complex interrelations between protein conformation and energetics.

Effects of hyperosmolarity and ion substitutions on amino acid efflux from the ischemic rat cerebral cortex

The contributions of sodium and chloride ions and of osmotic stresses to the ischemia-evoked efflux of excitotoxic and other amino acids were explored using a rat four vessel occlusion model. Replacement of Na+ with choline or N-methyl-D-glucamine (NMDG) and of Cl- with sulfate or gluconate was used to evaluate the contribution that these ions make to amino acid efflux. The contribution of ischemia-evoked swelling to amino acid release was studied by applying mannitol or sucrose to minimize the cell volume increases and the compensatory regulatory volume decrease evoked efflux of amino acids. Aliquots of artificial cerebrospinal fluid (aCSF), appropriately adjusted for ion replacement or 150 mM mannitol or sucrose, were pipetted into cortical cups 35 min prior to ischemia and perfusate samples were obtained prior to, during and following ischemia (20 min) and reperfusion (40 min). Replacement of Na+ by NMDG depressed basal (normoxic) efflux of most amino acids, with choline substitution having little effect. During ischemia NMDG substitution increased glutamate and GABA efflux and choline enhanced the release of aspartate, glutamate, GABA and taurine. A reduction in extracellular Na+ would facilitate reversal of Na+-dependent transporters with extrusion of amino acids. Another possible explanation for the elevated release is that the absence of Na+ would inhibit the Ca2+/Na+ counter transport system, with a deleterious accumulation of intracellular Ca2+. Chloride replacement with sulfate or gluconate enhanced the efflux of aspartate, glutamate, GABA and taurine during ischemia. Removal of Cl- would depolarize cells, and block the Cl--dependent action of inhibitory amino acid transmitters, with both actions enhancing the ischemic injury and, consequently, amino acid release. Exposure to hyperosmotic mannitol (150 mM) aCSF enhanced ischemia-evoked release of some amino acids (taurine, GABA) and decreased that of aspartate and phosphoethanolamine. Sucrose aCSF enhanced the ischemia-evoked release of most amino acids. A potential explanation for these observations is that both agents may be able to rapidly penetrate the plasma membranes of ischemic neurons, actually contributing to the release of other osmolytes. The unanticipated nature of many of the observations made during these manipulations of the aCSF serves to accentuate the complex nature of the mechanisms responsible for the ischemia-evoked amino acid efflux into the interstitial spaces.

Free radical involvement in endothelium-dependent responses of the rat thoracic aorta in moderate hypoxic conditions

This study investigates the effects of agents which act on the production or efficacy of free radicals on the hypoxic responses of rat aorta rings. Under moderate hypoxic conditions, the resting tension of the rings was not changed but in rings precontracted with 5-hydroxytryptamine, there was a relaxation followed by a contraction. Removal of the endothelium with saponin suppressed relaxation to acetylcholine and abolished the contractions produced by hypoxia. In rings with a functional endothelium, hypoxic vasoconstriction was strongly inhibited by mannitol and exifone, but was not reduced by N(G)-nitro-L-arginine methyl ester, superoxide dismutase + catalase, or deferoxamine. Hypoxic vasodilatation was only partially inhibited by mannitol. To conclude, hypoxic constriction of the rat thoracic aorta is largely endothelium-dependent and involves free radicals whereas hypoxic dilatation is partially endothelium-dependent and partially involves free radicals. There is also indirect evidence for lack of direct involvement of nitric oxide/endothelium-derived relaxing factor (NO*/EDRF), hydroxyl radical (OH*) and superoxide anion in the hypoxic constriction and relaxation of the rat aorta.

The effects of mannitol, albumin, and cardioplegia enhancers on 24-h rat heart preservation

During 24 h in vitro heart preservation and reperfusion, tissue damage occurs that seriously reduces cardiac function. Prevention of free radical production during preservation and reperfusion of ischemic tissue using free radical scavengers is of primary importance in maintaining optimal heart function in long-term preservation protocols. We examined whether mannitol (68 mM) and albumin (1.4 microM) in combination with other cardioplegia enhancers decreased free radical formation and edema and increased cardiac function during 24-h cold (5 degrees C) heart preservation and warm (37 degrees C) reperfusion in the Langendorff-isolated rat heart. The performance of mannitol-treated hearts was significantly decreased compared with that of hearts without mannitol treatment after 24 h of preservation with regard to recovery of diastolic pressure, contractility (+dP/dt), relaxation (-dP/dt), myocardial creatine kinase release, coronary flow, and lipid peroxidation. Albumin-treated hearts demonstrated higher cardiac function (contractility and coronary flow especially) than hearts not treated with albumin or hearts treated with mannitol, and this appears to be due to the positive effects of increased cellular metabolism and the enhancement of membrane stability.

Photo-oxidative killing of human colonic cancer cells using indocyanine green and infrared light

Despite of the approval of Photofrin in various countries, chemically defined sensitizers for photodynamic therapy (PDT) are still needed for the absorption of light in the infrared spectrum, which provides a maximal penetration of light into tissue. Therefore, both the efficacy and the mechanism of action of the clinically approved dye indocyanine green (ICG) and laser irradiation were investigated in vitro. For the investigation of phototoxic effects, HT-29 cells were incubated 24 h prior to irradiation by using different concentrations of ICG (10-500 microM). In each experiment, cells were irradiated using a continuous wave (cw)-diode laser (lambda(ex) = 805 nm, 30 J cm(-2), 40 mW cm(-2)). After laser irradiation, cell viability of dark control and of cells incubated with 500 microM ICG was 1.27+/-0.11 or 0.28+/-0.05 respectively. Using 100 microM ICG and D2O, cell viability was further decreased from 0.46+/-0.03 (H2O) to 0.11+/-0.01 (D2O). Using D2O and 100 microM ICG, the concentration of malondialdehyde, a marker of lipid peroxidation, increased from 0.89+/-0.10 nmol 10(-6) cells to 11.14+/-0.11 nmol 10(-6) cells. Using 100 microM ICG and laser irradiation sodium azide or histidine (50 mM), quenchers of singlet oxygen reduced the cell killing significantly. In contrast, when using mannitol, a quencher of superoxide anion and hydroxyl radical, cell killing was not inhibited. According to the present results, photoactivated ICG seems to kill colonic cancer cells due to the generation of singlet oxygen and the subsequent formation of lipid peroxides. Therefore, ICG might present a promising photosensitizer for PDT; first clinical results confirm these findings.

The physiological properties of human red cells as derived from kinetic osmotic volume changes

Volume changes were originally used for studying the dynamic properties of glucose transport in red cells. As an extension it has been found possible to examine the interplay of three functional proteins evolved for the physiological role of human erythrocytes in transporting carbon dioxide and bicarbonate. The proteins chiefly concerned in this investigation were the cytoplasmic carbonic anhydrase and the two membrane transporting proteins, namely the band 3 anion exchanger and the unique bicarbonate transporter, which are distinct from the anion exchanger. The rates of anion membrane transport measured and the volume changes may be more than two orders of magnitude faster than those which regulate cationic movement in red cells, but this may only be an adaptation for the physiological role of red cells. The new concepts derived from the studies and their possible wider applications to physiological mechanisms are briefly discussed.

Apoptosis in developing anthers and the role of ABA in this process during androgenesis in Hordeum vulgare L

Intra-nucleosomal cleavage of DNA into fragments of about 200 bp was demonstrated to occur in developing anthers, in which microspores had developed into the mid-late to late uni-nucleate stage in situ, i.e. at the verge of mitosis. The same was observed, but to a much larger extent, if these anthers were pre-treated by a hyper-osmotic shock. Pretreatment of anthers before the actual culture of microspores was required for optimal androgenesis of microspores. The use of the TUNEL reaction, which specifically labels 3' ends of DNA breaks, after intra-nucleosomal cleavage of DNA, revealed that DNA fragmentation mainly occurred in the loculus wall cells, tapetum cells and filament cells. TUNEL staining was absent or infrequently observed in the microspores of developing anthers in situ. Electron microscopy studies showed condensed chromatin in nuclei of loculus wall cells in the developing anthers. These observations at the chromatin and DNA level are known characteristics of programmed cell death, also known as apoptosis. Features of apoptosis were infrequently found in microspores from freshly isolated mature anthers. However, most tapetum cells had disappeared in these anthers and the remaining cell structures showed loss of cellular content. The viability of microspores in pre-treated anthers was comparable to those in freshly isolated anthers and almost four times higher than in anthers from control experiments. This observation was correlated with three to four times less microspores showing TUNEL staining and a two times higher level of ABA in the anther plus medium samples than in controls. Addition of ABA to the controls enhanced the viability and lowered the occurrence of apoptosis linked characteristics in the microspores. These data suggest that pre-treatment is effective in stimulating androgenesis because it leads to an increase in ABA levels which protects microspores from dying by apoptosis.

Effect of compensatory organic osmolytes on resistance to freeze-drying of L929 cells and of their isolated chromatin

(1) Compensatory organic osmolytes are stabilizers of macromolecular structures. During acclimation to dehydration or high salinity, they accumulate in cells and effectively protect them against disruption that might otherwise result from increased inorganic ion concentrations. (2) Circular and electric dichroism, analysis of the kinetics of digestion by micrococcal nuclease, and UV spectra between 190 and 305 nm were used to investigate the resistance to dehydration upon freezing or freeze-drying that could confer such compounds to chromatin isolated from cultured L929 cells. Some work was also done on intact cells in vivo. (3) Sorbitol, sucrose, and trehalose appear to protect isolated chromatin very effectively; proline is less effective. (4) These compounds also effectively protect chromatin from the disrupting effects of NaCl. (5) Cells loaded and grown with sorbitol, sucrose, or proline can tolerate larger decreases in hydration than control cells. They cannot, however, tolerate complete dehydration.

Mannitol at clinical concentrations activates multiple signaling pathways and induces apoptosis in endothelial cells

BACKGROUND AND PURPOSE

Hyperosmotic mannitol therapy is widely used in the clinical setting for acute and subacute reduction in brain edema, to decrease muscle damage in compartment syndrome, and to improve renal perfusion. Though beneficial rheological effects commonly are attributed to mannitol, its direct effects on endothelial cells are poorly understood.

METHODS

We studied the effect of hypertonic and hypotonic stress on bovine aortic endothelial (BAE) cells, using mannitol, urea, and sodium chloride and medium dilution in vitro.

RESULTS

Exposure to incremental osmolar concentrations of 300 mOsm of each osmotic agent increased apoptosis in BAE cells (mannitol congruent withNaCl>urea). Induced programmed cell death was detected by DAPI staining of intact cell nuclei, and by TUNEL and DNA fragmentation ladder assays. Mannitol-induced apoptosis exhibited dose dependence (42% of cells at 300 mOsm [P<0.0001] compared with 1.2% of control cells) and was also observed in bovine smooth muscle cells. Mannitol-induced apoptosis was attenuated approximately 50% in the presence of cycloheximide or actinomycin D. Hypertonic mannitol and NaCl, but not urea, increased tyrosine phosphorylation of the focal adhesion contact-associated proteins paxillin and FAK. Hypotonic medium, which did not lead to apoptosis, increased protein tyrosine phosphorylation of FAK but not of paxillin. Addition of mannitol or NaCl also produced sustained increases in c-Jun NH2-terminal kinase (JNK) activity. In addition, hypertonic mannitol increased intracellular free [Ca2+] in a dose-dependent manner. Chelation of intracellular Ca2+ with quin2-AM (10 micromol/L) inhibited mannitol-induced apoptosis approximately 50%, as to a lesser extent did inhibition of tyrosine kinase activity with herbimycin (1 micromol/L).

CONCLUSIONS

We have shown that hypertonic mannitol exposure induces endothelial cell apoptosis, accompanied by activation of tyrosine and stress kinases, phosphorylation of FAK and paxillin, and elevation of intracellular free [Ca2+]. The apoptosis is attenuated by inhibition of transcription or translation, by inhibition of tyrosine kinases, or by intracellular Ca2+ buffering. These data suggest that clinical use of the osmotic diuretic mannitol may exert direct deleterious effects on vascular endothelium.

Prevention of acute hyponatremia by mannitol: an unanticipated mechanism

PURPOSE

To evaluate the effectiveness and mode of action of the osmotic diuretic mannitol to prevent the development of acute hyponatremia in a setting designed to mimic the acute hyponatremia observed on the day of surgery.

RESULTS

Hyponatremia (129+/-1 mM, fall of 10+/-1 mM, p <0.01) was induced by the intraperitoneal administration of half-isotonic saline plus DDAVP to rats (n = 8); hyponatremia was due to a positive balance of electrolyte-free water (EFW). Rats given mannitol (10 mmol/kg body wt) in addition to the hypotonic saline plus DDAVP had only a minor degree of hyponatremia (plasma [Na+] 136+/-1 mM, fall 3+/-2 mM, p >0.05). All the mannitol given was excreted over the 16 h of observation, but the urine volume was not higher in these rats. The higher rate of excretion of EFW was due to a marked reduction in the rate excretion of Na+ with mannitol. This antinatriuresis was also present when mannitol was given intravenously.

CONCLUSIONS

Although mannitol increased the excretion of EFW, the mechanism required an enhanced renal reabsorption of Na+ rather than an increase in the urine flow rate.

Urea inhibits the Na-K pump in human erythrocytes

Recent studies have established that urea alters the activity of several volume-sensitive cation transport pathways. However, it has remained unclear whether urea has any effect on transport pathways that are not volume-sensitive. We examined the effect of urea on Na-K pump in the human erythrocytes. In cells from nine subjects, 500 mM urea inhibited 52 +/- 10% of the pump activity measured as the ouabain-sensitive (OS) K influx. Urea inhibited the OS K influx reversibly, in a concentration-dependent manner. [3H] oubain binding, a measure of the number of Na-K pump sites remained unchanged with urea. Urea decreased the Vmax for ouabain-sensitive K influx, but did not alter the apparent K(m) for external K. Furthermore, urea did not alter the apparent K(m) for intracellular Na. The ion turnover per pump site was decreased in the presence of urea. Thus, physiologically relevant urea concentration inhibit the Na-K pump in human erythrocyte. The inhibition of the Na-K pump by urea suggests that the effects of urea may not be limited to volume-sensitive transporters, but may be more widespread.

Luciferase: a sensitive and quantitative probe for blood-brain barrier disruption

A novel method for quantitative analysis of blood-brain barrier (BBB) disruption is described, using luciferase as a probe in a murine model system. Purified luciferase was delivered to mouse brain by osmotic BBB disruption with hypertonic mannitol; control animals received an intracarotid inoculation of saline prior to infusion of luciferase. Delivery of luciferase to brain tissue was then assessed by enzyme assay of tissue extracts, and by immunohistochemical staining. Luciferase activity in the brain of mannitol-treated animals was found to be significantly elevated (approx. sevenfold), when compared to activity in control (saline-treated) mice. This finding was confirmed by quantitative immunohistochemical staining of tissue sections, using a luciferase-specific antibody. These studies showed that there was an eight-fold elevation in the level of extravascular luciferase particles within the brain of mannitol-treated animals, as compared to controls. Taken together these data show that purified recombinant luciferase can be used as a sensitive probe, with which to study the integrity of the BBB.

Comparative effects of glycerol and Urografin on cochlear blood flow and serum osmolarity

Glycerol, an osmotic diuretic, has been used for the diagnosis and treatment of endolymphatic hydrops. Hearing improvements in hydropic ears are attributed to its dehydrating effect. In addition to this effect, glycerol also increases cochlear blood flow. Urografin, another hyperosmotic agent used for vasography, is similarly known to increase local blood flow. The present study compared these two hyperosmotic agents, glycerol and Urografin, in their effects on cochlear blood flow and serum osmolarity. Laser Doppler flowmetry on the lateral wall of the cochlea revealed that the increase in cochlear blood flow with a 30-min infusion (0.025 ml/min) of 76% Urografin continued for a longer time than with a 30-min infusion (0.025 ml/min) of 50% (v/v) glycerol. The significant increases appeared at 20 and 30 min after the infusion with the former; 10, 20, 30, 40, 50 and 60 min after the infusion with the latter. Intravenous infusion of these agents also caused elevation in serum osmolarity. This elevation was appreciably greater with Urografin infusion (maximal increase: about 30 mOsm on average) than with glycerol infusion (maximal increase: about 6 mOsm on average), and the former elevation appeared to be longer lasting than the latter. These differences were ascribed to differences between glycerol and Urografin with respect to the creation of an osmotic gradient across the capillary walls of cochlear blood vessels. Since glycerol penetrates the interstitial space and moves into inner ear fluids, the gradient may decline faster. It would be assumed that a higher concentration of the hyperosmotic agent in the capillary blood causes more vasodilatation and lowering of blood viscosity. Alternatively, direct action of these agents on the vascular wall may affect some biological processes, leading to vasodilatation in different degrees and durations with different agents. Hearing improvement with glycerol administration in hydropic ears was also discussed from the perspective of cochlear blood flow.

[Intestinal permeability in the first year of life. The effect of diarrhea]

OBJECTIVE

The permeability of the intestinal mucosa to lactulose and mannitol was explored longitudinally in infants at 1, 3-4 and 11-12 months of age. This was also evaluated during the episodes of diarrhea that they suffered during follow-up.

PATIENTS AND METHODS

Sugar excretion was measured by gas chromatography in five-hour urine samples.

RESULTS

A decrease in lactulose excretion was observed, which became significant at 11-12 months of age (p = 0.02). No changes were detected in mannitol excretion, although this showed a tendency to decrease. The lactulose/mannitol (L/M) ratio remained unchanged. During the 15 episodes of diarrhea observed in these infants during the 12 month follow-up, a considerable increase in this ratio was seen, due mainly to increased lactulose excretion.

CONCLUSIONS

It is hypothesized that the decrease in lactulose excretion between one and 11-12 months of age is part of the maturational process of the intestinal barrier, while diarrhea results in increased permeability due to damage to the absorptive epithelium.

Effect of high-glucose concentrations on the expression of collagens and fibronectin by fibroblasts in culture

Extracellular matrix macromolecules such as collagen and fibronectin are progressively altered during aging and age-related diseases like diabetes. We investigated the effect of high-glucose concentration (mimicking diabetic conditions) and the influence of in vitro cell aging [comparing 4th-passage fibroblasts (P4) to 15th-passage fibroblasts (P15)] on collagen and fibronectin synthesis. Fibroblasts were incubated at postconfluency with radiolabeled precursors, [3H] proline for collagen, [35S] methionine for fibronectin. We report that in control conditions (5 mM glucose) collagen III production increased with in vitro cell aging. High glucose concentrations (10 and 15 mM) increased specifically collagen III synthesis both at the mRNA and protein levels, without alteration of collagen I production in P4 and P15 cells. Fibronectin synthesis was also increased both during in vitro cell aging and in high glucose-treated P4 fibroblasts. Taken together, these data suggest similarities between changes of phenotypic expression of collagen and fibronectin induced by in vitro cell aging and conditions imitating diabetes.

An acute experiment on retrograde intestinal peristalsis with emesis using decerebrated dogs

This acute experiment using decerebrated dogs was a new model for studies of central and peripheral mechanisms of intestinal motility with emesis, and was undertaken to clarify the relationship between intestinal contractions and the retrograde transport of intestinal contents with emesis. Contractility of the small intestine was recorded by five force transducers. Reflux of mannitol solution injected into the small intestine through the proximal duodenum was recorded by a magnetic flow meter. Retching was induced by vagal afferent stimulation, intramuscular apomorphine, or intragastric copper sulfate. Intestinal contractility was enhanced preceding retching caused by these emetic stimuli. Characteristic contractions in the oral direction were observed in the small intestine before and during retching. These contractions originated in the caudal or middle intestine and conducted to the duodenum intermittently, rather than continuously. Reflux of mannitol solution to the proximal duodenum was observed just after the initiation of retching, and was sometimes observed repeatedly during retching. These results suggest that intestinal contents are repeatedly transported to the proximal duodenum during retching by intermittent retrograde contractions. Acute experiments using decerebrated dogs seem to be useful and essential for studies of central and peripheral mechanisms of emesis.

The influence of mannitol on renal function during and after open-heart surgery

Mannitol is often included in the priming solution of the heart-lung machine used during cardiopulmonary bypass (CPB). This study was set up to evaluate the effect of different doses of mannitol on human patients. Patients receiving 10 g of mannitol (n = 18) had an increased diuresis only during the bypass period (mean time = 87 min) when compared with a control group (n = 19) who did not receive mannitol. Patients receiving 20 g of mannitol (n = 19) had a significantly greater diuresis than both the control group and the 10 g group and the diuresis continued on throughout the immediate postbypass period (total mean time approximately 3 h). Patients receiving 30 g of mannitol (n = 20) also had a significantly greater diuresis that continued on during the first hour in the intensive care unit (ICU) (total mean time approximately 4 h). After 6 h in the ICU, all three groups of mannitol-treated patients equally demonstrated a trend towards an increased diuresis over the control group, which became a significant increase by 12 h in the ICU (p = 0.001) despite indications that the mannitol had been cleared from the body. These results suggest that there is an improvement of renal function post-CPB if mannitol is included in the CPB prime which may be due to an amelioration of the ischaemic effects of bypass on the kidneys.

A decrease in renal medullary tonicity stimulates anion transport in Henle's loop of rat kidneys

To investigate the effect of reduction in renal medulla osmolality on loop of Henle (LOH) net bicarbonate reabsorption, clearance and microperfusion experiments were performed on Sprague-Dawley rats. The decrease of renal medulla osmolality was induced by intravenous infusion of either a large dose of mannitol (mannitol protocol) or a hypotonic solution (hypotonic protocol) delivered at a rate to match the sodium and bicarbonate load of the control period. During the mannitol protocol, clearance data demonstrated a rise in glomerular filtration rate (GFR), renal plasma flow, urine pH, and fractional bicarbonate excretion. On the contrary, microperfusion experiments, performed in the absence of mannitol in the tubular perfusate, revealed a significant increase both in the absolute and fractional LOH bicarbonate transport. During the hypotonic protocol, there was a decrease in GFR, associated with an increase in fractional excretion of bicarbonate. In the microperfusion experiments, hypotonic saline, similar to mannitol, stimulated absolute and fractional LOH bicarbonate transport. Net reabsorption of chloride, measured under the same experimental conditions, was also found to be activated. Therefore, the intravenous infusion of hypotonic solution affected the LOH transepithelial net reabsorption of both bicarbonate and chloride. We hypothesize that the increase in the transport rate of these two anions, along the same segment and in similar experimental conditions, may be mediated, at least in part, by decreased medullary tonicity, which is one factor common both to hypertonic mannitol and hypotonic saline infusion.

Degeneration in vivo of rat hippocampal neurons by wild-type Alzheimer amyloid precursor protein overexpressed by adenovirus-mediated gene transfer

In an attempt to elucidate the pathological implications of intracellular accumulation of the amyloid precursor protein (APP) in postmitotic neurons in vivo, we transferred APP695 cDNA into rat hippocampal neurons by using a replication-defective adenovirus vector. We first improved the efficiency of adenovirus-mediated gene transfer into neurons in vivo by using hypertonic mannitol. When a beta-galactosidase-expressing recombinant adenovirus suspended in 1 M mannitol was injected into a dorsal hippocampal region, a number of neurons in remote areas were positively stained, presumably owing to increased retrograde transport of the virus. When an APP695-expressing adenovirus was injected into the same site, part of the infected neurons in the hippocampal formation underwent severe degeneration in a few days, whereas astrocytes near the injection site showed no apparent degeneration. These degenerating neurons accumulated different epitopes of APP, and beta/A4 protein (Abeta)-immunoreactive materials were undetected in the extracellular space. A small number of degenerating neurons showed nuclear DNA fragmentation. Electron microscopic examinations demonstrated that degenerating neurons had shrunken perikarya along with synaptic abnormalities. Microglial cells/macrophages were often found in close proximity to degenerating neurons, and in some cases they phagocytosed these neurons. These results suggest that intracellular accumulation of wild-type APP695 causes a specific type of neuronal degeneration in vivo in the absence of extracellular Abeta deposition.

Effect of glucose on the expression of the angiotensinogen gene in opossum kidney cells

To investigate whether D(+)-glucose has a stimulatory effect on the expression of the angiotensinogen (Ang) gene in opossum kidney (OK) cells, we used OK cells with a fusion gene containing various lengths of the 5'-flanking regulatory sequence of the rat Ang gene fused with the human growth hormone (hGH) gene as a reporter, stably integrated into their genomes. The level of expression of the fusion gene was quantified by the amount of immunoreactive-human growth hormone (IR-hGH) secreted into the medium. The addition of D(+)-glucose stimulated the expression of pOGH (Ang N-1498/+18) in OK 27 cells in a dose-dependent manner (5 to 25 mM), whereas the addition of D-mannitol, L-glucose and 2-deoxy-D-glucose (25 mM) had no effect. The stimulatory effect of D(+)-glucose (25 mM) was blocked by the presence of staurosporine or H7 (an inhibitor of protein kinase C) or U73122 (an inhibitor of phospholipase C and A2) but not blocked by the presence of Rp-cAMP (an inhibitor of cAMP-dependent protein kinase A). The addition of D(+)-glucose (25 mM) also stimulated the expression of pOGH (Ang N-960/+18) and pOGH (Ang N-688/+18) in OK 960 and OK 688 cells, respectively. It had no stimulatory effect, however, on the expression of pOGH (Ang N-280/+18) and pOGH (Ang N-35/+18) in OK 280 and OK 35 cells, respectively. The addition of D(+)-glucose also had no effect on the expression of pTKGH in OK 13 cells, an OK cell line, into which had been stably integrated a fusion gene, pTKGH containing the promoter/enhancer DNA sequence of the viral thymidine-kinase (TK) gene fused with a human growth hormone gene as a reporter. These studies demonstrate that the stimulatory effect of high D(+)-glucose concentration (25 mM) on the expression of the angiotensinogen-growth hormone fusion genes in OK cells is mediated via the 5'-flanking region of the angiotensinogen gene and the protein kinase C signal transduction pathway. Our data indicate that a high glucose concentration may activate the renin-angiotensin system in the renal proximal tubular cells.

In vivo and in vitro regulation of [3H]glyburide binding to brain sulfonylurea receptors in obesity-prone and resistant rats by glucose

Select brain neurons increase their firing rate when ambient glucose levels rise, possibly via a neuronal ATP-sensitive K+ (KATP) channel and its associated sulfonylurea receptor (SUR). We used receptor autoradiographic binding of 20 nM [3H]glyburide (in the presence or absence of Gpp(NH)p which blocks binding to low-affinity sites) to assess the in vivo and in vitro effects of altering glucose availability upon high- and low-affinity binding to brain SUR. Since the brain's ability to monitor and regulate glucose metabolism is critical to maintenance of energy balance, testing was done in chow-fed male Sprague-Dawley rats which had an underlying predisposition to develop either diet-induced obesity (DIO-prone) or to be diet-resistant (DR-prone) when subsequently fed a high-energy diet. Under control conditions, both in vivo and in vitro studies showed DIO-prone rats to have reduced levels of low-, but not high-affinity [3H]glyburide binding in most forebrain areas. As compared to equiosmolar infusions of mannitol, 60 min unilateral intracarotid glucose infusions at 4 mg/kg/min in awake rats reduced low-affinity [3H]glyburide binding in numerous hypothalamic and amygdalar areas of both DR- and DIO-prone rats with little effect on high-affinity binding. Only in the paraventricular nucleus of DR-prone rats was there a phenotype-specific downregulation of low-affinity binding. Brain sections from other rats were incubated with [3H]glyburide in the presence of 0, 5 or 10 mM glucose. The resultant in vitro effects of glucose were more variable and widespread than intracarotid infusions. Here, glucose often increased low-affinity [3H]glyburide binding, particularly in DR-prone rats at 5 mM. Again, there was little effect on high-affinity binding. Thus, glucose may affect the firing of glucose-responsive neurons by indirectly altering KATP channel function via its effects on low-affinity cell body SUR.

Deep cervical lymph flow following the infusion of mannitol in rabbits

Jugular lymph flow of anesthetized rabbits in response to infusion of mannitol solutions differing in osmolarity were measured. Either an isotonic (310 mosmol), hypotonic (100 mosmol), or hypertonic (605 mosmol) mannitol solution was infused into either the internal carotid artery (ICA) or the right lateral ventricle (RLV). Lymph was collected continuously and measured over a 60 min preinfusion period, as well as during mannitol infusion and intermittent recovery periods. The mean peak flow rates of hypertonic infusion for the first 30 min via ICA and RLV were 2.2 +/- 0.4 (12% decrease) and 5.0 +/- 1.0 microliter/min (72% increase), over those of isotonic infusates which were 2.5 +/- 0.3 microliters/min (via ICA) and 2.9 +/- 0.5 microliters/min (via RLV), respectively. In contrast, lymph flow rates of hypotonic infusate for the first 30 min via ICA and RLV were 3.9 +/- 0.8 microliters/min and 2.3 +/- 0.4 microliters/min, respectively. A decrease both in intracranial pressure and in lymph flow following hypertonic mannitol infusion via ICA were observed. However, intracranial pressure and lymph formation were increased following hypertonic infusion via RLV. The results indicate that the changes in jugular lymph flow could be affected by the changing in osmolarity of mannitol infusate.

Inhalation of dry-powder mannitol increases mucociliary clearance

Inhalation of hypertonic saline stimulates mucociliary clearance (MCC) in healthy subjects and those with obstructive lung disease. We investigated the effect of inhaling the osmotic agent mannitol on MCC. We used a dry-powder preparation of mannitol British Pharmacopea (BP) which was encapsulated and delivered using a Dinkihaler. MCC was measured for 75 min in six asthmatic and six healthy subjects on two occasions before and after the mannitol inhalation or its control, using 99mTc-sulphur colloid and a gamma camera. The inhaled dose of mannitol was 267+/-171 mg (mean+/-SD) and 400 mg and the percentage fall in forced expiratory volume in one second (FEV1) was 22+/-3 and 4+/-2% in the asthmatic and healthy subjects, respectively. The total clearance in the whole right lung for the 60 min from the start of inhalation of mannitol was greater by 263+/-11.9% in the asthmatic and 18.1+/-4.9% in the healthy subjects compared to the control. The total clearance over 75 min was 54.7+/-9.6% and 33.6+/-9.4% on the mannitol and control day (p<0.002), respectively, in the asthmatic subjects and 40.5+/-7.1% and 24.8+/-7.8% (p<0.002) in the healthy subjects. In conclusion, inhalation of dry-powder mannitol increases mucociliary clearance in asthmatic and healthy subjects and may benefit patients with abnormal mucociliary clearance.

Time course of cerebral edema after traumatic brain injury in rats: effects of riluzole and mannitol

Brain trauma is the main cause of morbidity and mortality in young adults. One delayed events that occurs after a head trauma and compromises the survival of patients is cerebral edema. The present study examined first the occurrence of cerebral edema after a traumatic brain injury (TBI) induced by moderate fluid percussion in rats. Brain water content was measured from 1 h to 7 days posttrauma, in the hippocampus and cortex, on both ipsi- and contralateral hemispheres. Second, the effects of mannitol, an osmotic agent frequently used in the clinic, and riluzole, a neuroprotective compound, were investigated on regional edema formation. After TBI, the ipsilateral edema began early at 1-6 h, was maximal at 48 h and was resorbed by 5-7 days. No edema was observed in the contralateral hemisphere. Mannitol at 1 g/kg or vehicle was administered iv 15 min, 2 h and 4 h postinjury. At this dose, mannitol significantly attenuated the ipsilateral injured cortex edema measured at 6 h (p < 0.05). Riluzole at 4 and 8 mg/kg or vehicle was administered 15 min (IV) and 6 h, 24 h, and 30 h (SC) post-TBI. Riluzole at 4 x 4 mg/kg significantly reduced edema measured at 48 h, in the ipsilateral hippocampus (p < 0.05), whereas at 4 x 8 mg/kg, the reduction was observed in the hippocampus (p < 0.01) and the injured cortex (p < 0.05). Our results demonstrate that (1) cerebral edema begins early after the injury and is resorbed over 1 week; (2) mannitol could attenuate cerebral edema; and (iii) riluzole in addition to its neuroprotective effects reduces the brain edema. Thus, riluzole could be useful in human TBI treatment.

Flavobacterium breve meningitis in a dog

An unusual, gram-negative rod was isolated in significant numbers (4+) from the cerebrospinal fluid (CSF) of a dog. This isolate, Flavobacterium breve, has not been identified previously as a pathogen in the dog. The case and the characteristics of the organism are described.

Quantification and predictors of plasma volume expansion from mannitol treatment

OBJECTIVE

To determine the effects of acute hypertonic mannitol infusion on intravascular volume expansion and to identify potential predictors of hypervolemia.

DESIGN

Measurements of plasma volume and volume regulatory hormones were performed in healthy volunteers before and over 90 min after acute infusion of 20% mannitol solution in a therapeutic dose of 0.5 g/kg body weight, equalling an average infusion volume of 180 ml.

SETTING

Clinical research unit in an 800-bed teaching hospital in the eastern part of Switzerland.

PARTICIPANTS

Eight normal male volunteers.

MEASUREMENTS AND RESULTS

Baseline plasma volume was determined by the indocyanine green dye dilution technique. Serial plasma protein measurements were performed after mannitol infusion to calculate intravascular volume changes. Mannitol administration resulted in a plasma expansion that persisted for more than 90 min and peaked at 112% of the baseline plasma volume 15 min after infusion. Concomitantly, an increase in systolic blood pressure and a fall in plasma sodium concentration occurred. Pharmacokinetic analyses of mannitol distribution and elimination revealed a close relation between plasma volume expansion and mannitol serum concentrations. While renin activity and aldosterone concentrations were suppressed proportionally to the intravascular volume increase, antidiuretic hormone was increased despite notable volume expansion and hyponatremia. Similarly, a rise in atrial natriuretic peptide was detected.

CONCLUSIONS

Therapeutic doses of hypertonic mannitol cause substantial plasma volume expansion, resulting in increased blood pressure. Plasma volume expansion is related to mannitol serum concentrations and mannitol clearance determines the time required to restore normovolemia. ADH and ANP are potentially aggravating factors of mannitol-induced hyponatremia.

Quantitative measurements of regional cerebral blood volume using MRI in rats: effects of arterial carbon dioxide tension and mannitol

A three-dimensional (3D) T1-weighted sequence was used to acquire high spatial resolution whole brain images in rats before and after the injection of an intravascular contrast agent. These T1-weighted images were used to estimate regional cerebral blood volume (rCBV) as a percentage of blood volume in each voxel. Ventilation was manipulated to investigate the effects of altered arterial carbon dioxide tension (PaCO2) on rCBV. In addition, different doses of a hypertonic mannitol solution were used to investigate the sensitivity of the proposed method in a serial monitoring paradigm. An rCBV of 2.40% +/- 0.34% was obtained before any physiological manipulation, in good agreement with literature values using alternative techniques. Using this method, it was found that there exists a linear relationship between PaCO2 and rCBV (R2 = 0.77) and that rCBV increased in a dose and time dependent fashion in mannitol-treated rats. High signal-to-noise was available due to the substantial increase in blood signal from the intravascular contrast agent.

Contrast media induced changes in tubular electrophysiology and glomerular filtration rate in the mouse kidney

The isolated perfused mouse proximal tubule was used to examine electrophysiologic effects of diatrizoate and ioversol. Luminal or basolateral application of diatrizoate resulted in a dose-dependent, reversible hyperpolarization of the proximal tubule cell basolateral membrane potential (VB), which could be abolished by the addition of 10 microM probenecid. While there was a modest reduction in intracellular ATP following a 60-min exposure to diatrizoate, there was no deterioration of VB after 90 min of diatrizoate exposure, even following a 20-min hypoxic insult. Ioversol did not elicit an electrical response. Neither diatrizoate nor ioversol significantly affected transepithelial potential (VT) in the isolated perfused medullary thick ascending limb. In vivo studies showed that only the ionic contrast agent diatrizoate significantly reduced glomerular filtration rate, by 70%. The observed acute contrast media induced reduction in glomerular filtration rate does not appear to depend on direct renal tubular cytotoxicity.

[Diuretics for therapy of patients with hypertension]

Diuretic agents have antihypertensive effects mainly be decreasing extracellular volume and cardiac output. These diuretics are described with regard to mechanism of action, site of action, adverse effects, and drug interactions. Thiazide diuretics inhibit the Na(+)-Cl- symporter in the distal convoluted tubule, by competing for the Cl- binding site, and increase Na+ and Cl- excretion. Loop diuretics are inhibitors of Na(+)-K(+)-2Cl- symporter in the thick ascending limb of the loop of Henle. However, loop diuretics are not the diuretic of first choice and should be reserved for patients in whom other diuretics or antihypertensive drugs do not result in a satisfactory response. The potassium sparing diuretics are used primarily to reduce the kaliuresis and potenciate the hypotensive effect of a thiazide.

Effect of tumor necrosis factor-alpha on the permeability of bovine brain microvessel endothelial cell monolayers

The administration of chemotherapy to patients with tumors of the central nervous system is often blocked by the blood-brain barrier. Tumor necrosis factor-alpha (TNF-alpha) is a cytokine that promotes vascular permeability in addition to its pro-inflammatory effects. However, no direct evidence exists as to whether TNF-alpha may increase permeability of the BBB. We evaluated the effect of TNF-alpha on the transport of cisplatin (CDDP) or high molecular weight dextran labeled with fluorescein isothiocyanate (FITC-dextran) across bovine brain microvessel endothelial cell (BMEC) monolayers that was conducted on side-by-side diffusion chambers in vitro. The permeability coefficient for the transport of CDDP across the untreated monolayer was 3.80 x 10(-5) cm sec-1 at 30 minutes. After treating the BMEC monolayer with TNF-alpha (50 U ml-1 and 500 U ml-1) for 36 hours, the PC of CDDP increased significantly to 8.94 x 10(-5), and 14.43 x 10(-5) cm sec-1 respectively (p < 0.01). TNF-alpha had no effect on the transport of FITC-dextran across the BMEC monolayers. Electron microscopy showed that the tight junctions between the BMECs persisted even after treatment with TNF-alpha, whereas they had been partially disrupted following exposure to mannitol, 1600 mOsm kg-1. TNF-alpha selectively promoted the in vitro permeability of the blood-brain barrier to CDDP without disrupting tight junctions. This system could be used as a model for experimental studies of chemotherapy. Findings suggested that the combined administration of TNF-alpha and CDDP may be clinically useful.

Multiple-dose mannitol reduces brain water content in a rat model of cortical infarction

BACKGROUND AND PURPOSE

Repeated use of mannitol in the setting of ischemic infarction is a controversial and poorly defined therapeutic intervention. The purpose of this study was to examine the effects of repeated mannitol infusions on brain water content and tissue pressure in a well-defined rat model of focal ischemic stroke.

METHODS

Mannitol infusions (0.5, 1.5, or 2.5 g/kg) were given by intravenous bolus 4 or 24 hours after 90-minute transient cortical ischemia in the territory of the right middle cerebral artery in rats and every 4 hours thereafter for a total of 24 hours. Fluid replacement was limited to 0.5 mL i.v. isotonic saline administered immediately after each mannitol dose. Control rats received 0.5 mL i.v. saline at the same intervals and were otherwise under ad libitum conditions. Water contents (percent H2O) of whole hemispheres and of cortical biopsies were measured with the wet-dry method, and blood samples were analyzed for plasma osmolality and chemistries. In a subgroup of rats, tissue pressure was also measured within the hemisphere ipsilateral to the infarct.

RESULTS

Repeated mannitol infusions resulted in a dose-dependent increase in plasma osmolality and a dose-dependent decrease in the percent H2O of the ischemic middle cerebral artery cortex and ipsilateral hemisphere. In contrast, percent H2O of the contralateral cortex and hemisphere was significantly decreased only in the groups given the highest dose of mannitol (2.5 g/kg). Mannitol infusions at a dose of 1.5 g/kg begun 24 hours after reperfusion were also associated with a significant reduction of tissue pressure.

CONCLUSIONS

In a rat model of ischemic cortical infarction, repeated mannitol infusions resulted primarily in a decrease in the percent H2O of the infarct and ipsilateral hemisphere, as well as decreased tissue pressure.

Tracing the Na/K-ATPase with rubidium

Rubidium (Rb) was used as a marker ion for K to assess Na/K(Rb)-ATPase activity in single renal tubule cells. Initial Rb uptake rates were measured by electron microprobe analysis in individual tubule cells of the rat kidney during acute stimulation or during inhibition of transepithelial Na absorption. Under these conditions, Rb uptake closely correlates with intracellular Na concentrations, indicating that the intracellular Na concentration is a major determinant in the precise adjustment of basolateral, Na/K(Rb)-ATPase-dependent Na extrusion to Na entry across the apical cell membrane. Chronically increased distal Na delivery induced by loop diuretics triggers adaptive processes which allow increased transcellular Na movement at normal or near-normal intracellular Na concentrations.

Effects of acetylcholine, carbachol, and mannitol on rabbit corneal endothelial function as assessed by corneal deturgescence

BACKGROUND

Anterior chamber miotic solutions are widely used in ophthalmic surgery to induce pupillary contraction. We investigated whether the acetylcholine, carbachol, or mannitol present in perfusing solutions can affect corneal endothelial function.

METHODS

Freshly dissected deepithelized rabbit corneas were mounted in a Dikstein-Maurice chamber at 36 degrees C. The endothelial sides were perfused with six solutions: (A) 55 mM (1%) acetylcholine Cl plus modified balanced salts; (B) control for A, with acetylcholine Cl replaced by sucrose; (C) 0.55 mM (0.01%) carbachol Cl plus balanced salts; (D) balanced salts solution (BS; control for C); (E) 3% mannitol plus modified balanced salts; and (F) modified balanced salts (control for E, with mannitol replaced by sucrose). Corneal thickness was followed for 3 h in each experiment. The effect of solution E did not differ from that of solution F.

RESULTS

The carbachol-containing solution produced a small increase in corneal thickness compared to the control solution, while the acetylcholine-containing solution resulted in corneal thickness lower than that in control preparations.

CONCLUSION

From these data, acetylcholine is harmless to the endothelium, and may actually stimulate its fluid pump mechanism. Carbachol, on the other hand, appears to have a detrimental effect.

Diabetic-induced endothelial dysfunction in rat aorta: role of hydroxyl radicals

OBJECTIVE

Previous studies suggest a role of superoxide anion radicals (.O2-) in impaired endothelium-dependent relaxation of diabetic blood vessels; however, the role of secondary reactive oxygen species remains unclear. In the present study, we investigated a role of various potential reactive oxygen species in diabetic endothelial dysfunction.

METHODS

Thoracic aortic rings from 8-week streptozotocin-induced diabetic and age-matched control rats were mounted in isolated tissue baths. Endothelium-dependent relaxation to acetylcholine (ACH) and endothelium-independent relaxation to nitroglycerin (NTG) were assessed in precontracted rings.

RESULTS

ACH-induced relaxation was impaired in diabetic compared to control rings and was not improved with either indomethacin or daltroban. ACH-induced relaxation in both control and diabetic rings was completely blocked with the nitric oxide synthase inhibitors, L-nitroarginine methyl ester or L-nitroarginine (L-NA). NTG-induced relaxation was insensitive to L-NA and was unaltered by diabetes. Pretreatment with superoxide dismutase (SOD) at activities which did not alter contractile tone failed to alter response to ACH in diabetic rings. Similar results were obtained using either catalase or mannitol. In contrast, the combination of SOD plus catalase or DETAPAC, an inhibitor of metal-facilitated hydroxyl radical (.OH) formation, markedly enhanced relaxation to ACH in diabetic but not in control rings. Neither the combination of SOD plus catalase nor DETAPAC altered the sensitivity or relaxation to NTG in control rings with or without endothelium. In diabetic rings with endothelium, both DETAPAC or SOD plus catalase increased sensitivity but not maximum relaxation to NTG. In diabetic rings without endothelium, relaxation and sensitivity to NTG were unaltered by either treatment. In L-NA-treated diabetic rings with endothelium, sensitivity and relaxation to NTG was unaltered by either DETAPAC or SOD plus catalase.

CONCLUSION

Diabetic endothelium produces increases in both .O2- and H2O2 leading to enhanced intracellular production of .OH. Thus, .OH are implicated in diabetes-induced endothelial dysfunction.

Effect of seizures and diuretics on the osmolality of the cerebrospinal fluid

There was a significant increase in the osmolality of the cerebrospinal fluid (CSF) of the anesthetized rats after treatment with 80 mg/kg (but not 39 mg/kg) furosemide and 1 g/kg of mannitol, but not during seizures induced by kainic acid. Furosemide (10 mg/kg) blocked seizure activity by kainic acid, while mannitol (1 g/kg) did not. The results suggest that the antiepileptic effect of furosemide is due to a direct CNS effect not related to a change in CSF osmolality.