Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 132-146).

Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Dec. 23, 2009). Includes bibliographical references (p. 110-121).

No description available.

The metabolic heat generated by exercise must be dissipated to maintain body temperature within narrow physiological limits; during exercise and heat exposure, body water is lost via sweating to enable evaporative cooling of the body. When sweating takes place, total body water is reduced (without the intake of additional fluids) from each fluid compartment due to the free exchange of water between compartments with a concomitant loss of electrolytes, primarily sodium. A series of three investigations were undertaken to evaluate: 1) the efficacy of acute sodium citrate-chloride loading on endurance trained males and females as a viable means to expand extracellular fluid volume, 2) any menstrual cycle effects on renal handling of this sodium load at rest, and 3) if any subsequent hypervolaemia reduces the physiological strain of exercise in warm conditions in both genders. The first investigation examined eight endurance-trained (VO₂[max]: 58 ml�kg⁻��min⁻� (SD 5); 36 y (SD 11)) runners in a randomized double-blind crossover study. The participants ingested a high-sodium (HighNa⁺: 164 mmol Na⁺�L⁻�) or low-sodium (LowNa⁺: 10 mmol Na⁺�L⁻�) beverage (10 ml�kg⁻�) before running to exhaustion at 70% VO₂[max] in warm conditions (32�C, 50% RH, V[a]~1.5 m�s⁻�). Results indicate that HighNa⁺ increased PV before exercise (4.5% (SD 3.7)), calculated from Hct and [Hb]), whereas LowNa⁺ didn�t (0.0% (SD 0.5); P = 0.04), and involved greater time to exercise termination in those who were stopped due to ethical end point of 39.5�C and volitional exhaustion (39.5�C: 57.9 min (SD 6) vs. 46.4 min (SD 4); n = 5, P = 0.04; EXH: 96.1 min (SD 22) vs. 75.3 min (SD 21); n = 3, P = 0.03; HighNa⁺ vs. LowNa⁺ respectively). At equivalent times before exercise termination, HighNa⁺ also involved lower core temperature (38.9 vs. 39.3�C; P = 0.00) and perceived exertion (P = 0.01), and a tendency for lower heart rate (164 vs. 174 bpm; P = 0.08). The main purpose of the second investigation was to investigate the efficacy of an acute sodium load on endurance trained women�s plasma volume and renal mechanisms across the menstrual cycle at rest. This was evaluated by inducing a sodium-mediated plasma volume expansion using HighNa⁺ at rest during the last high hormone week of the OCP cycle (HH[ocp]) or the late-luteal phase of the natural cycle (LUT[nat]) and during the low hormone sugar pill week of the OCP cycle (SUG[ocp]) or during the early follicular phase of the natural cycle (FOL[nat]. Thirteen women completed the study with one woman on a progestin-only pill (results were used for case study, not statistical analyses) and were assigned to one of two groups: 1) control (NAT, n = 6, 24 y (SD 5), 53 ml�kg�ml⁻� (SD 3)) or oral contraceptive pill (OCP, n = 6, progestin only n = 1, 29 y (SD 6), 51 ml�kg�ml⁻� (SD 2)) group according to their usage status. Across the four-hour post loading time there was greater plasma volume expansion in SUG[ocp] and FOL[nat] vs. LUT[nat] and HH[ocp] (5.06% (SD1.16) vs. 3.35% (SD 0.23), P = 0.02). OCP usage did not reliably alter the hypervolaemic response (P = 0.27), and this was not dependent on phase of cycle (P = 0.32). Plasma volume expansion occurred across both types and phases of the menstrual cycle with evidence that estradiol interactions with AVP, P[osm] and body water retention are stronger in the low hormone phase of the OCP than in the follicular phase of the natural cycle; illustrated by greater overall water retention after an acute sodium+water load. The third investigation was conducted during the high hormone phase of both OCP and NAT menstrual cycles to further examine sodium-loading effects on the physiological capacity of exhaustive cycling in warm conditions. Thirteen endurance-trained (VO₂[peak] 52 ml�kg⁻��min⁻� (SD 2); 26 y (SD 6), 60.8 kg (SD 5), mean (SD)) cyclists completed this double-blind, crossover experiment during the high hormone phase of the menstrual cycle. Cyclists ingested a concentrated sodium (HighNa⁺: 164 mmol Na⁺�L⁻�) or low-sodium (LowNa⁺: 10 mmol Na⁺�L⁻�) beverage (10 ml�kg⁻�) before cycling to exhaustion at 70% VO₂[max] in warm conditions (32�C, 50% RH, V[a]~5.6 m�s⁻�). HighNa⁺ increased PV before exercise, similar to that of the men in the first investigation, whereas LowNa⁺ didn�t (4.4% (SD 1.2) vs. -1.9% (SD 1.3); P < 0.0001), and involved greater time to exhaustion (98.6 min (SD 25.6) vs. 78.5 min (SD 24.6); P < 0.0001). There was a higher baseline core temperature and faster rate of change for HH[ocp] for both beverage conditions (HighNa⁺: 37.15 (SD 0.6) vs. 36.92�C (SD 0.4); P = 0.05, LowNa⁺: 37.04 (SD 0.6) vs. 36.90�C (SD 0.4), P = 0.05; HH[ocp] vs. LUT[nat], respectively). Through this series of investigations a greater understanding was achieved of fluid balance and the effect of pre-exercise hypervolaemia between genders; pre-exercise ingestion of a concentrated sodium beverage increased plasma volume before exercise and involved less thermoregulatory and the actual and perceived physiological strain during exercise and increased endurance in warm conditions.

No description available.

The metabolic heat generated by exercise must be dissipated to maintain body temperature within narrow physiological limits; during exercise and heat exposure, body water is lost via sweating to enable evaporative cooling of the body. When sweating takes place, total body water is reduced (without the intake of additional fluids) from each fluid compartment due to the free exchange of water between compartments with a concomitant loss of electrolytes, primarily sodium. A series of three investigations were undertaken to evaluate: 1) the efficacy of acute sodium citrate-chloride loading on endurance trained males and females as a viable means to expand extracellular fluid volume, 2) any menstrual cycle effects on renal handling of this sodium load at rest, and 3) if any subsequent hypervolaemia reduces the physiological strain of exercise in warm conditions in both genders. The first investigation examined eight endurance-trained (VO₂[max]: 58 ml�kg⁻��min⁻� (SD 5); 36 y (SD 11)) runners in a randomized double-blind crossover study. The participants ingested a high-sodium (HighNa⁺: 164 mmol Na⁺�L⁻�) or low-sodium (LowNa⁺: 10 mmol Na⁺�L⁻�) beverage (10 ml�kg⁻�) before running to exhaustion at 70% VO₂[max] in warm conditions (32�C, 50% RH, V[a]~1.5 m�s⁻�). Results indicate that HighNa⁺ increased PV before exercise (4.5% (SD 3.7)), calculated from Hct and [Hb]), whereas LowNa⁺ didn�t (0.0% (SD 0.5); P = 0.04), and involved greater time to exercise termination in those who were stopped due to ethical end point of 39.5�C and volitional exhaustion (39.5�C: 57.9 min (SD 6) vs. 46.4 min (SD 4); n = 5, P = 0.04; EXH: 96.1 min (SD 22) vs. 75.3 min (SD 21); n = 3, P = 0.03; HighNa⁺ vs. LowNa⁺ respectively). At equivalent times before exercise termination, HighNa⁺ also involved lower core temperature (38.9 vs. 39.3�C; P = 0.00) and perceived exertion (P = 0.01), and a tendency for lower heart rate (164 vs. 174 bpm; P = 0.08). The main purpose of the second investigation was to investigate the efficacy of an acute sodium load on endurance trained women�s plasma volume and renal mechanisms across the menstrual cycle at rest. This was evaluated by inducing a sodium-mediated plasma volume expansion using HighNa⁺ at rest during the last high hormone week of the OCP cycle (HH[ocp]) or the late-luteal phase of the natural cycle (LUT[nat]) and during the low hormone sugar pill week of the OCP cycle (SUG[ocp]) or during the early follicular phase of the natural cycle (FOL[nat]. Thirteen women completed the study with one woman on a progestin-only pill (results were used for case study, not statistical analyses) and were assigned to one of two groups: 1) control (NAT, n = 6, 24 y (SD 5), 53 ml�kg�ml⁻� (SD 3)) or oral contraceptive pill (OCP, n = 6, progestin only n = 1, 29 y (SD 6), 51 ml�kg�ml⁻� (SD 2)) group according to their usage status. Across the four-hour post loading time there was greater plasma volume expansion in SUG[ocp] and FOL[nat] vs. LUT[nat] and HH[ocp] (5.06% (SD1.16) vs. 3.35% (SD 0.23), P = 0.02). OCP usage did not reliably alter the hypervolaemic response (P = 0.27), and this was not dependent on phase of cycle (P = 0.32). Plasma volume expansion occurred across both types and phases of the menstrual cycle with evidence that estradiol interactions with AVP, P[osm] and body water retention are stronger in the low hormone phase of the OCP than in the follicular phase of the natural cycle; illustrated by greater overall water retention after an acute sodium+water load. The third investigation was conducted during the high hormone phase of both OCP and NAT menstrual cycles to further examine sodium-loading effects on the physiological capacity of exhaustive cycling in warm conditions. Thirteen endurance-trained (VO₂[peak] 52 ml�kg⁻��min⁻� (SD 2); 26 y (SD 6), 60.8 kg (SD 5), mean (SD)) cyclists completed this double-blind, crossover experiment during the high hormone phase of the menstrual cycle. Cyclists ingested a concentrated sodium (HighNa⁺: 164 mmol Na⁺�L⁻�) or low-sodium (LowNa⁺: 10 mmol Na⁺�L⁻�) beverage (10 ml�kg⁻�) before cycling to exhaustion at 70% VO₂[max] in warm conditions (32�C, 50% RH, V[a]~5.6 m�s⁻�). HighNa⁺ increased PV before exercise, similar to that of the men in the first investigation, whereas LowNa⁺ didn�t (4.4% (SD 1.2) vs. -1.9% (SD 1.3); P < 0.0001), and involved greater time to exhaustion (98.6 min (SD 25.6) vs. 78.5 min (SD 24.6); P < 0.0001). There was a higher baseline core temperature and faster rate of change for HH[ocp] for both beverage conditions (HighNa⁺: 37.15 (SD 0.6) vs. 36.92�C (SD 0.4); P = 0.05, LowNa⁺: 37.04 (SD 0.6) vs. 36.90�C (SD 0.4), P = 0.05; HH[ocp] vs. LUT[nat], respectively). Through this series of investigations a greater understanding was achieved of fluid balance and the effect of pre-exercise hypervolaemia between genders; pre-exercise ingestion of a concentrated sodium beverage increased plasma volume before exercise and involved less thermoregulatory and the actual and perceived physiological strain during exercise and increased endurance in warm conditions.

Different drugs which can affect various aspects of sodium transport were tested on contractile activity of a variety of vascular smooth muscles. In the rabbit anterior mesenteric-portal vein, diphenylhydantoin sodium (DPH) attenuated the contractile responses to noradrenaline (NA) and the inhibition was reversible by washing. The p-hydroxy derivative, 5-p-hydroxyphenyl)-5-phenylhydantoin (DPHOH), which was reported to lack the anticonvulsant activity and the inhibitory effect of DPH on insulin secretion was without any effect on the rabbit anterior mesenteric vein. The inhibitory effect of DPH on contractile responses to NA was almost abolished by prior treatment with ouabain and in K-free solutions. Evidence of a Na-Ca interaction is provided by the finding that both low Na and high Ca Krebs attenuates the inhibitory effect of DPH while low Ca Krebs accentuates it. Electrolyte studies using rat tail arteries showed that DPH could counteract the K loss and Na gain produced by either ouabain containing or K-deficient solutions. Prior cooling of the tissue for one hour at 1° C. and then testing the effect of DPH in K-deficient solutions at 1° C., abolished the ability of DPH to counteract the electrolyte changes in K-deficient solutions. DPH in normal Krebs solution did not significantly affect the Na content of rat tail arteries. Under this condition, there was a slight diminution in the K content. The results suggest that DPH can stimulate the Na pump in rat tail arteries under conditions In which Na and Rare going along their electrochemical gradient, and/or under conditions simulating the depolarized state. In normal Krebs, DPH does not seem to stimulate the Na pump of rat tail arteries. Under such experimental conditions, our data are more suggestive of an inhibition of the Na-K ATPase. Evidence is also provided that the attenuation of contractile responses to NA in the rabbit anterior mesenteric vein, might be related to stimulation of the Na pump. Further studies were done to outline the effect of alteration of other parameters of Na transport in vascular smooth muscles. Ouabain and ethacrynic acid, both inhibitors of the Na-K ATPase, produced a characteristic pattern of response in the rabbit anterior mesenteric vein. There was at first a contraction, followed by relaxation, which was followed by more persistent contractures at higher doses. The diuretic agent, amiloride, which is reported to inhibit the passive Na influx in a variety of tissues, was found to attenuate contractile responses to NA in rabbit aortic strips, A.M.V., and rat tail arteries. In aortic strips its effect was specific on the rapid phase of NA contraction. Since the rapid phase is believed to be the result f the release of a more tightly bound Ca⁺⁺ pool, the latter effect suggests that amiloride affects mainly the availability of a bound Ca pool to the contractile protein. Our results so far suggest that alteration of different parameters of the Na transport might be involved in altering the amount of ionized Ca⁺⁺ available to the contractile protein. More studies on this subject are needed and might open the way for a better understanding of the Na-Ca interaction in vascular smooth muscles and their possible relation to the hypertensive state. Further experiments were done to study the relaxation of the rabbit anterior mesenteric vein following contractile responses. It seems that extracellular Na is involved in the relaxation of the rabbit anterior mesenteric vein following contractile responses, since this tissue, when contracted in low Na solutions, would not relax unless some of the Na is returned to the Krebs solution. Li could not substitute for Na in this function since the contracture occurred in low Na solutions irrespective of whether the substitute was Tris-HCl or Li. the latter was even more effective than Tris-HCl in inducing contractures in low Na Krebs. Moreover, relaxation of the rabbit anterior mesenteric vein, following contractile responses to NA was delayed in low Na Krebs irrespective of whether the substitute was Li or Tris-HCl. Preliminary electron microscopic studies were carried on rabbit anterior mesenteric veins to evaluate the effect of the inhibitors of the ATPase, ethacrynic acid and ouabain, on ultrastructure. Both drugs induced disruption of the myofibrillar structures in doses of 1 mM and 10⁻⁵ M, respectively, when the tissue was exposed to the drug for 2 hours. An impressive finding was the dramatic diminution in the number of plasma-lemmal vesicles in the ethacrynic acid treated tissue. This finding raises the possibility that the formation of these vesicles might be an energy dependent process and opens the way for further studies to evaluate their possible importance in active ionic transport processes. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate

No description available.

The epithelial sodium channel (ENaC) made up of α, β and γ subunits is located at the apical membrane of polarised epithelia and mediates transport of sodium ions into the cells. Tight control of ENaC function is essential for maintaining sodium homeostasis, blood volume and blood pressure. Controlling the number of active channels present at the cell surface appears to be critically important in regulating ENaC activity. The neural precursor cell expressed developmentally down-regulated gene 4 (Nedd4) family of proteins (eg. Nedd4-2) ubiquitinate ENaC and decrease its cell surface expression. The activity of Nedd4-2 is modulated by serum and glucocorticoid-induced kinase (SGK), which phosphorylates Nedd4-2 and increases cell surface expression of ENaC. The c̲o̲pper m̲etabolism gene M̲URR1 d̲omain 1 (COMMD1) protein is a recently identified ENaC binding partner and negative regulator of channel activity. Studies by other groups suggest that COMMD1 is also involved in the processes of intracellular protein trafficking and ubiquitin-dependent protein degradation. The aims of this study were 1). To characterise the interactions between COMMD1 and ENaC. 2). To identify the mechanism(s) by which COMMD1 down-regulates ENaC activity. Here protein-protein interaction studies were used to show that a recently identified conserved C-terminal domain (the COMM domain) in COMMD1 is essential for its binding to ENaC. The binding site for COMMD1 in βENaC was found to be located in its N-terminal domain. COMMD1 was shown to down-regulate ENaC by increasing ubiquitin modification of ENaC and by decreasing the cell surface population. COMMD1 was found to interact with SGK and formed a complex with SGK and Nedd4-2. Ussing chamber studies of Na⁺ transport showed that COMMD1 attenuated the stimulation of ENaC by SGK and abolished insulin-stimulated ENaC current in epithelial cells. Conversely, knock-down of COMMD1 increased ENaC current in mammalian epithelial cells. These data suggest that COMMD1 plays a role in regulating ENaC activity in epithelial cells and its effect is likely mediated via SGK. In addition COMMD1 was found to bind to the adaptor protein subunit [mu]2. Mutations in COMMD1 that disrupt its interaction with [mu]2 impair its ability to decrease cell surface expression of ENaC in Cos-7 cells, therefore COMMD1 may also have a role in the endocytosis of ENaC by linking cell surface ENaC to the clathrin-dependent endocytosis machinery. In summary, this study investigated the interactions between COMMD1 and ENaC and identified that the SGK/Nedd4-2 pathway is involved in the COMMD1-mediated ubiquitination and down-regulation of ENaC activity.

Thesis (Ph.D.)--University of Alberta, 2010. / A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Medical Sciences, Biomedical Engineering, Department of Electrical and Computer Engineering. Title from pdf file main screen (viewed on April 11, 2010). Includes bibliographical references.