sodium-cyanate and Hypoxia

Sodium cyanate (NaOCN) first appeared on the biomedical scene as a potential therapeutic agent for sickle-cell disease. Although it did not fulfill its early promise in the clinic, it proved to be useful as a pharmacological tool in physiological research, particularly in the physiology of oxygen transport. NaOCN has been especially valuable in the area of investigation which is reviewed here: the study of oxygen transport, both in normoxic and in hypoxic conditions, in experimental models in which NaOCN was used to induce a shift to the left of the oxygen dissociation curve. The classical idea is that a low Hb-O2 affinity is of adaptive value for life at high altitudes but it has been challenged by several pieces of evidence. One of them is the demonstration of increased survival in hypoxic hypoxia of animals with a high Hb-O2 affinity induced by NaOCN. We also discuss the advantages and potentially confounding factors which should be taken into consideration when interpreting results of studies in which the oxygen dissociation curve has been modified by administration of NaOCN.

Topics: Altitude; Anemia, Sickle Cell; Animals; Cyanates; Embryonic and Fetal Development; Erythropoiesis; Hemoglobins; Humans; Hypoxia; Pulmonary Ventilation

It is difficult task to measure precisely the toxic effect of beta-amyloid (Aβ 1-42) peptides and also the protective effect of novel drug candidates against Aβ-peptides. The widely used MTT-assay in cell lines or primary cell cultures could be insensitive against Aβ-peptides. We describe here an easy and relevant method for testing Aβ 1-42 toxicity on acute hippocampal slices derived from rat. Brain slice viability in different conditions was measured using MTT and LDH assays. The concomitant use of these two assays can give detailed and relevant results on the toxic effect of Aβ 1-42 in oxygen-glucose deprived (OGD) acute brain slice model. Both assays are capable of quantifying tissue viability by measuring optical density (OD). We found that simultaneous application of OGD and Aβ 1-42 treatment induced a more intensive decrease in hippocampal slice viability than their separate effects. The use of MTT and LDH assay for quantifying brain slice viability proved to be an easy ex vivo method for investigating Aβ toxicity. Testing brain slices is more relevant in Alzheimer's Disease research than using in vitro cell cultures, due to maintenance of the three dimensional cellular network, the cell variability and intact cell connections.

Topics: Amyloid beta-Peptides; Analysis of Variance; Animals; Animals, Newborn; Cyanates; Glucose; Hippocampus; Hydrogen Peroxide; Hypoxia; In Vitro Techniques; L-Lactate Dehydrogenase; Male; Peptide Fragments; Rats; Rats, Wistar; Tetrazolium Salts; Thiazoles

Ducks are well-known to be more tolerant to asphyxia than non-diving birds, but it is not known if their defences include enhanced neuronal hypoxia tolerance. To test this, we compared extracellular recordings of spontaneous activity in the Purkinje cell layer of 400 mum thick isolated cerebellar slices from eider ducks, chickens and rats, before, during and after 60 min hypoxia (95%N(2)-5%CO(2)) or chemical anoxia (hypoxia + 2 mM NaCN). Most slices rapidly lost activity in hypoxia, with or without recovery after rinse and return to normoxia (95%O(2)-5%CO(2)), but some maintained spontaneous activity throughout the insult. Proportions of 'surviving' (i.e. recovering or active) duck slices were significantly higher than for chickens in anoxia, and relative activity levels were higher for ducks than for chickens during hypoxia, anoxia and recovery. Survival of rat slices was significantly poorer than for birds under all conditions. Results suggest that (1) duck cerebellar neurons are intrinsically more hypoxia-tolerant than chicken neurons; (2) avian neurons are more hypoxia-tolerant than rat neurons, and (3) the enhanced hypoxic tolerance of duck neurons largely depended on efficient anaerobiosis since it mainly manifested itself in chemical anoxia. Mechanisms underlying the observed differences in neuronal hypoxic responses remain to be elucidated.

Topics: Action Potentials; Animals; Cerebellum; Chickens; Cyanates; Ducks; Hypoxia; In Vitro Techniques; Male; Neurons; Oxygen; Periodicity; Rats; Rats, Wistar; Statistics, Nonparametric; Time Factors

Deficiency in energy supply, such as occurs during hypoxia, anoxia, metabolic stress and mitochondrial failure, strongly affects the excitability of central neurons. Such lowered energy supply evokes various changes in spontaneous synaptic input to the hippocampal and cortical neurons. However, how this energy deprivation affects synaptic input to motor neurons, which are also vulnerable to energy deprivation, has never been addressed. Here we report for the first time the effect of metabolic stress on synaptic input to motor neurons by recording postsynaptic currents in the hypoglossal nucleus. Chemical anoxia with NaCN (1 mm) and anoxia with 95% N(2) induced a persistent inward current and a marked and robust increase in action potential-independent synaptic input. This increase was abolished by strychnine, but not by picrotoxin, CNQX or MK-801, indicating glycine release facilitation. Blockade of voltage-dependent Ca(2+) channels and extracellular Ca(2+) deprivation strongly attenuated this facilitation. The amplitude of inward currents evoked by local application of NMDA to the motor neurons in the presence of strychnine was significantly increased during NaCN application. A saturating concentration of d-serine occluded this potentiation, suggesting that released glycine activated the glycine-binding sites of NMDA receptors. By contrast, neurons in the dorsal motor nucleus of the vagus showed no detectable change in synaptic input in response to NaCN. These data suggest that increase in synaptically released glycine in response to metabolic stress may play an exacerbating role in NMDA receptor-mediated excitotoxicity in motor neurons.

Topics: Analysis of Variance; Animals; Animals, Newborn; Cyanates; Drug Interactions; Excitatory Amino Acid Agents; Glycine; Glycine Agents; Hypoxia; In Vitro Techniques; Inhibitory Postsynaptic Potentials; Membrane Potentials; Motor Neurons; Patch-Clamp Techniques; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Solitary Nucleus; Strychnine

This study examined whether a hypoxia-tolerant amphibian, the Cane toad, undergoes mammalian-like ventilatory acclimatisation to hypoxia (VAH) and whether chronic hypoxia (CH) alters NMDA-mediated regulation of the acute hypoxic ventilatory response (HVR). Toads were exposed to 10 days of CH (10% O2) followed by acute hypoxic breathing trials or an intra-arterial injection of NaCN. Trials were conducted before and after i.p. treatment with an NMDA-receptor channel blocker (MK801). CH blunted the acute HVR but did not alter resting breathing. MK801 did not alter resting ventilation. In control animals, MK801 augmented breathing frequency (fR) during acute hypoxia by increasing the number of breaths per episode. This effect was attenuated following CH although MK801 did enhance the number of episodes per minute during acute hypoxia. MK801 enhanced the fR response to NaCN in both groups. The results indicate that CH did not produce mammalian-like VAH (i.e. increased resting ventilation and an augmented acute HVR) but did alter MK801-sensitive regulation of breathing pattern and the acute HVR.

Topics: Acclimatization; Analysis of Variance; Animals; Bufo marinus; Cyanates; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Hypoxia; N-Methylaspartate; Pulmonary Ventilation; Respiration; Time Factors

Cyanate derivatives such as NaOCN have been known to increase the hypoxia tolerance of animals by increasing the affinity of hemoglobin (Hb) to O(2). To clarify the mechanism of this increase in hypoxia tolerance, we examined changes in metabolic rate and cardiovascular parameters during a hypoxia test in halothane-anesthetized, NaOCN-treated and spontaneously breathing rats (50 mg/kg/d S.C., 10 d). Control animals received saline. The capillary density in the skeletal muscle (sternocleidomastoid muscle), cardiac papillary muscle and medulla oblongata was also examined histologically. The Hb-O(2) affinity index, P(50), decreased from 38 (control rat) to 24 mmHg in NaOCN-treated rats. During hyperoxic gas breathing, the rat treated with NaOCN showed a significantly lower metabolic rate (V(.)O(2), V(.)CO(2)), higher cardiac stroke volume, slower heart rate, lower PvO(2), and lower O(2) extraction ratio than those in control rats. The NaOCN-treated rats exhibited well-maintained arterial blood pressure and a larger cardiac output response to reduction in FIO(2) to 0.10-0.08. The increase in O(2) extraction ratio with reduction in FIO(2) was larger in NaOCN-treated than in control rats. The circulatory and metabolic depressions at FIO(2) 0.05 were effectively attenuated in NaOCN-treated rats. The capillary density of the cardiac muscle and medulla oblongata but not the skeletal muscle was significantly higher in NaOCN-treated rats than in control rats. The greater hypoxia tolerance in NaOCN-treated rats is ascribed to the combined effects of left shift of Hb-O(2) dissociation curve, lower basal V(. )O(2), higher capillary density in the heart, and brain, and other adaptive mechanisms induced probably by prolonged tissue hypoxia.

Topics: Acute Disease; Animals; Cardiovascular System; Cyanates; Hemoglobins; Hypoxia; Male; Oxygen; Rats; Rats, Wistar

The efficacy of an increased hemoglobin oxygen affinity [decreased oxygen half-saturation pressure of hemoglobin (P50)] on capillary oxygen transport was evaluated in the hamster retractor muscle under conditions of a severely limited oxygen supply resulting from the combined effects of a 40% reduction in systemic hematocrit and hypoxic ventilation (inspired oxygen fraction 0.1). Two groups of hamsters were utilized: one with a normal oxygen affinity (untreated; P50 = 26.1 +/- 2.4 Torr) and one with an increased oxygen affinity (treated; P50 = 15.7 +/- 1.4 Torr) induced by the chronic short-term administration of sodium cyanate. Using in vivo video microscopy and image analysis techniques, we determined oxygen saturation and associated hemodynamics at both ends of the capillary network. During hypoxic ventilation, the decrease in oxygen saturation across the network was 3.6% for untreated animals compared with 9.9% for treated animals. During hypoxia, estimated end-capillary PO2 was significantly higher in the untreated animals. These data indicate that, at the capillary level, a decreased P50 is advantageous for tissue oxygenation when oxygen supply is severely compromised, because normal oxygen losses in capillaries are maintained in treated but not in untreated animals. The data are consistent with the presence of a diffusion limitation for oxygen during severe hypoxia in animals with a normal hemoglobin oxygen affinity.

Topics: Animals; Capillaries; Cricetinae; Cyanates; Hemodilution; Hemoglobins; Hypoxia; Male; Mesocricetus; Muscles; Oxygen; Oxygen Consumption; Oxyhemoglobins

The impact of an increased hemoglobin oxygen affinity (decreased P50) on oxygen transport was evaluated in capillaries of the retractor muscle under nonhypoxic (FIo2 = 0.30 and 0.21) and hypoxic (FIo2 = 0.10) conditions in hamsters with normal oxygen affinity [control; P50 = 26.1 +/- 1.0 (SD) mmHg, n = 12] and in hamsters with an increased oxygen affinity [treated; P50 = 16.2 +/- 1.6 (SD) mmHg, n = 7] induced by chronic short-term administration of sodium cyanate. Using in vivo video microscopy and computer-aided image analysis, we determined oxygen saturation (SO2) and associated hemodynamic parameters in both arteriolar (n = 30 control, 18 treated) and venular (n = 25 control, 17 treated) capillaries. In response to hypoxia, systemic arterial PO2 decreased to 29.6 +/- 6.0 (SD) mmHg in control animals and 24.7 +/- 3.8 (SD) mmHg in treated animals associated with abrupt decreases in systemic arterial blood pressure and increases in respiratory rate. The decrease in SO2 across the capillary network during nonhypoxic ventilation was 13.3% SO2 for control animals and 11.0% SO2 for treated animals. During hypoxic ventilation, the decrease in SO2 was 9.1% SO2 in control animals and 8.7% SO2 in treated animals. Hemodynamic parameters were not significantly different in the two groups during hypoxia. Estimated end-capillary PO2 was significantly lower in the treated animals. These data indicate that an increased oxygen affinity does not provide an obvious advantage for oxygen transport during hypoxia at the level of the capillary network in resting striated muscle; however, such an advantage might become apparent in the presence of an increased metabolic rate or a more severe hypoxic challenge.

Topics: Animals; Biological Transport; Blood Circulation; Cricetinae; Cyanates; Hemodynamics; Hypoxia; Male; Microcirculation; Muscles; Oxygen; Partial Pressure; Respiration

This study investigated the activities of the tensor and levator veli palatini muscles related to respiration. During quiet breathing, no activity was observed in either muscle. With either hypercapnic or hypoxemic condition, the tensor veli palatini muscle exhibited phasic activity during inspiration. The levator veli palatini muscle showed phasic activity during expiration with hypoxemia (PaO2 less than 40 mm Hg). NaCN perfused bilaterally through the carotid sinus induced these respiratory activities. The tensor veli palatini muscle was more sensitive than the levator veli palatini muscle to NaCN.

Topics: Animals; Carbon Dioxide; Carotid Body; Carotid Sinus; Cyanates; Dogs; Electromyography; Hypercapnia; Hypoxia; Muscle Contraction; Oxygen; Palatal Muscles; Respiration

In order to evaluate the toxic effects of Sodium Cyanate (NaOCN), it was orally administered to growing mice at sea level (SL-CN) and to mice chronically exposed to intermittent hypobaric hypoxia (IHH-CN). The effects on body weight, in-vivo O2 consumption (VO2) and the respiratory function of liver mitochondria were evaluated. At sea level, the animals on cyanate lost weight in contrast with the controls that gained weight. When exposed to IHH, the controls lost weight and the animals on cyanate regained weight. After 2 months observation the weights of the IHH-CN and IHH-C were similar. The VO2 after one month of treatment was similar in the SL-C and in the SL-CN but it was lower in the IHH-CN when compared with IHH-C. The substrate-stimulated respiration of isolated liver mitochondria (ST4) was not affected by NaOCN, but the ADP-stimulated respiration (ST3) was reduced. The ratio ST3/ST4 (RCR) was also lower. These changes were present in both SL and in IHH and were much larger after three months of treatment. The toxic effects of chronic administration of NaOCN are discussed.

Topics: Administration, Oral; Animals; Atmospheric Pressure; Body Weight; Cyanates; Hypoxia; Male; Mice; Mitochondria, Liver; Oxygen Consumption

The effects on the ventilatory response to acute hypoxia of increasing the Hb-O2 affinity by NaOCN administration were studied in the halothane anesthetized spontaneously breathing rat. Increases in ventilation during the progressive hypoxia test were significantly augmented, and ventilatory depression occurring in severe hypoxia was clearly inhibited in the NaOCN-treated rat. Beneficial effects of NaOCN treatment probably result from the protection of respiratory regulating mechanism from functional deterioration in severe hypoxia.

Topics: Animals; Carbon Dioxide; Cyanates; Hypoxia; Male; Oxygen; Oxyhemoglobins; Partial Pressure; Rats; Rats, Inbred Strains; Reference Values; Respiration

Three weeks of sodium cyanate (NaCNO) intraperitoneal treatment in rats (n = 15) induced high hemoglobin O2 affinity, i.e., low PO2 at 50% hemoglobin saturation (P50), 20.5 +/- 1.4 Torr, in comparison with the mean control values, 34.5 +/- 1.6 Torr (n = 15). NaCNO rats showed a reduction in mean body weight, 376 +/- 27 g, in comparison with controls, 423 +/- 23 g (P less than 0.001). Despite arterial O2 partial pressure (PaO2) within normal limits NaCNO-treated rats had a higher systolic right ventricular pressure (SRVP), 33.7 +/- 3.1 Torr, in comparison with control value, 29.0 +/- 2.5 Torr (P less than 0.001). Right ventricle weights were significantly increased (P less than 0.001). After 60 min of an hypoxic challenge (fractional concentration of inspired O2 = 0.10) NaCNO-treated rats increased SRVP of only 7 +/- 4% compared with 46 +/- 9% in the control animals. Inducing high hemoglobin affinity in rats (n = 10; 6 wk NaCNO treatment) resulted in increases in hematocrit ratio and hemoglobin concentration (P less than 0.001). The characteristics of the red blood cell (RBC) itself changed; values of mean cell volume, mean cell hemoglobin, and mean cell hemoglobin concentration being significantly increased (P less than 0.001) when compared with mean control values. The count of nucleated RBC's appeared to be significantly higher from the 2nd wk of NaCNO treatment. Chronic NaCNO treatment was demonstrated to exert "hypoxia-like" effects since it induced prevention of normal growth, polycythemia, pulmonary hypertension, right ventricular hypertrophy, and blunted pulmonary pressor response to acute hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Chronic Disease; Cyanates; Erythrocyte Indices; Hemoglobins; Hypertension, Pulmonary; Hypoxia; Oxygen; Pulmonary Circulation; Rats; Vascular Resistance

Topics: Animals; Blood Gas Analysis; Body Weight; Cardiac Output; Chemical Phenomena; Chemistry, Physical; Cyanates; Hydrogen-Ion Concentration; Hypoxia; Lung; Male; Oxygen; Oxygen Consumption; Rats; Rats, Inbred Strains

The importance of hemoglobin-oxygen affinity (HOA) in affecting skeletal muscle oxygen consumption (VO2) was reevaluated using an isolated canine gracilis muscle. HOA of the blood [normal O2 half-saturation pressure of hemoglobin (P50) = 30 Torr] was increased by refrigerated storage (P50 = 22 Torr), incubation in sodium metabisulfite (P50 = 24 Torr), or in sodium cyanate (P50 = 14 Torr). Stored blood caused a significant fall in VO2 to 80% of control, with no change in venous O2 partial pressure (PvO2), substantiating previous studies. However, in contrast, blood incubated in sodium metabisulfite or sodium cyanate resulted in no impairment of VO2, with a fall in PvO2 in the latter case indicating that a critical PvO2 did not cause the reduction in VO2 with stored blood. To substantiate further the lack of existence of a critical PO2, fresh and increased HOA blood was perfused at constant flow rates and varying arterial oxygen saturations. Stored blood showed a marked reduction in VO2 as compared with normal blood over a wide range of saturations. However, carbamylated blood VO2 was identical to fresh blood VO2 values. The data suggest that the position of the oxygen dissociation curve may not be as important as originally thought in determining skeletal muscle oxygen delivery. The drop in VO2 caused by perfusion with stored blood is due to some other factor unrelated to HOA.

Topics: 2,3-Diphosphoglycerate; Animals; Blood; Blood Preservation; Cyanates; Diphosphoglyceric Acids; Dogs; Female; Hemoglobins; Hypoxia; Knee; Male; Muscles; Oxygen; Oxygen Consumption; Partial Pressure; Perfusion; Thigh; Veins