Modulation of erythrocyte band 4.1 binding by volume expansion

Erythrocyte band 4.1 is an important protein in the control and maintenance of the cytoskeleton. Skate erythrocyte band 3, the anion exchanger, appears to play a pivotal role in the regulation of volume-stimulated solute efflux during volume expansion. Because band 4.1 interacts with band 3, we tested whether their interaction might change during volume expansion. Skate red blood cells were volume-expanded in either hypotonic media (one-half osmolarity) or were swollen under isoosmotic conditions by inclusion of ethylene glycol or ammonium chloride in the medium. Microsomal membranes isolated from red cells under volume expanded conditions demonstrated a significant decrease in the amount of band 4.1 bound to band 3. In unstimulated cells, approximately one third of the binding of band 4.1 occurred to band 3. This binding was characterized as being sensitive to competition by the peptide IRRRY. The majority of band 4.1 is bound to glycophorin (as demonstrated in other species), and this binding does not change during volume expansion. The alteration in band 4.1:band 3 interaction occurs within 5 min after volume expansion and is transient, returning to near normal interaction within 60 min. Two drugs that promote band 3 oligomerization, pyridoxal-5'-phosphate and DIDS, also decreased band 4.1 interaction with band 3. Band 4.1 and ankyrin binding to band 3 may be reciprocally related as high-affinity ankyrin binding sites to band 3 observed under volume-expanded conditions are decreased by inclusion of band 4.1 in the binding reactions. J. Exp. Zool. 289:177-183, 2001.     

Albumin-induced plasma volume expansion: diurnal and temperature effects

To develop a reliable procedure for the acute expansion of plasma volume (PV), 26 male volunteers were randomly assigned to either a thermoneutral (25 degrees C and 40% relative humidity) or hot-dry (37 degrees C and 25% relative humidity) environment; subsequently each subject was seated for at least 1 h and then infused intravenously with either 100 or 200 ml of a 25% albumin solution or 0.9% saline. On the day before each infusion, PV was estimated by dye dilution using indocyanine green. Net percent change in PV (using hematocrit and hemoglobin values) was calculated at 1, 3, 6, 9, 12, and 24 h postinfusion. The PV of subjects residing in the heat after a 100-ml saline infusion increased significantly over 1-h values at 6, 9, and 12 h postinfusion but not at 24 h. The same trend, although not significant, was apparent at room temperature. The data suggest a slow isooncotic circadian pattern of PV expansion and contraction. The infusion of hyperoncotic albumin produced rapid expansion of plasma volume. With the low dose (25 g) at 1 h postinfusion, the expansion was 379 +/- 102 ml in the heat and 301 +/- 160 ml at room temperature. With the high dose (50 g) at 1 h postinfusion, the expansion was 479 +/- 84 ml in the heat and 427 +/- 147 ml at room temperature. The high dose produced an expansion that persisted for at least 9 h in subjects in either environment. The data suggest a mechanism for the retention of fluid during heat acclimatization and a useful procedure for plasma volume expansion in humans.     

Altitude acclimatization: influence on periodic breathing and chemoresponsiveness during sleep

Although the influence of altitude acclimatization on respiration has been carefully studied, the associated changes in hypoxic and hypercapnic ventilatory responses are the subject of controversy with neither response being previously evaluated during sleep at altitude. Therefore, six healthy males were studied at sea level and on nights 1, 4, and 7 after arrival at altitude (14,110 ft). During wakefulness, ventilation and the ventilatory responses to hypoxia and hypercapnia were determined on each occasion. During both non-rapid-eye-movement and rapid-eye-movement sleep, ventilation, ventilatory pattern, and the hypercapnic ventilatory response (measured at ambient arterial O2 saturation) were determined. There were four primary observations from this study: 1) the hypoxic ventilatory response, although similar to sea level values on arrival at altitude, increased steadily with acclimatization up to 7 days; 2) the slope of the hypercapnic ventilatory response increased on initial exposure to a hypoxic environment (altitude) but did not increase further with acclimatization, although the position of this response shifted steadily to the left (lower PCO2 values); 3) the sleep-induced decrements in both ventilation and hypercapnic responsiveness at altitude were equivalent to those observed at sea level with similar acclimatization occurring during wakefulness and sleep; and 4) the quantity of periodic breathing during sleep at altitude was highly variable and tended to occur more frequently in individuals with higher ventilatory responses to both hypoxia and hypercapnia.     

Effect of extracellular volume expansion on erythrocyte sodium transport in rats.

The effects of extracellular volume expansion (EVE) on the major sodium transport systems and sodium and potassium contents in rat erythrocytes have been examined in the present study. Study has been performed in anesthetized Wistar rat weighing about 300 g. Acute extracellular volume expansion (EVE) was induced by a constant intravenous saline infusion (3% body wt, 3 hours). Rats anaesthetized and catheterized but not expanded were used as controls. Arterial blood samples from control and expanded rats were obtained at the same time, and assayed immediately. Intracellular sodium and potassium concentration and ouabain sensitive (Na(+)-K(+)-pump) and bumetanide sensitive (Na(+)-K(+)-cotransport system) outward Na+ fluxes in erythrocytes were measured. The effect of plasma on erythrocyte transport was also analyzed by measuring 86Rb uptake. Neither of two plasma cations (Na+ and K+) were modified by the EVE. Also intracellular Na+ and K+ levels remained unvariable. Total Na+ efflux was not modified by EVE, but pump-mediated Na+ efflux was smaller after than before EVE. The ouabain-inhibible Na+ efflux rate constant decreased after EVE (from 687 +/- 81 to 525 +/- 29 h-1 x 10(-3); P less than 0.05). Both Na(+)-K(+)cotransport-mediated Na+ efflux and passive permeability increased significantly after EVE. The incubation with plasma from saline-infused animals induced a significant decrease in Rb uptake rate constant, that was not observed after incubation with plasma from non-expanded rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma volume expansion in rats: effects on thermoregulation and exercise

Administration of polyethylene glycol (PEG, intraperitoneal, 3 ml, 30% solution) to adult male rats (300 g) resulted in an approximately 20% increment in plasma volume (PV) 24 h after PEG injection. When these animals were exercised (9.14 m/min, level treadmill) in a warm (30 degrees C, 30-40% relative humidity) environment, their mean endurance was increased from 67.9 (saline-treated controls, CONT) to 93.6 min (P less than 0.01). Total water loss was increased from 12.2 (CONT) to 17.2 g (PEG, P less than 0.01). Atropine administration (ATR, 200 micrograms/kg, tail vein) significantly (P less than 0.05) reduced both the endurance and the salivary water loss of CONT and PEG-treated rats, whereas it increased the heating rate (P less than 0.01) of both groups. PEG treatment reduced (P less than 0.01) the hematocrit and circulating protein levels both before and subsequent to exercise in the warm environment. Clinical chemical indexes of heat/exercise injury were generally unaffected by pharmacological intervention, whereas clinical chemical responses to exercise were related to the endurance time of each group. We concluded that expansion of PV by PEG provided significant beneficial effects on performance and thermoregulation during exercise in a warm environment.     

The membrane volume occupied by anesthetic molecules: A reinterpretation of the erythrocyte expansion data

Seeman and coworkers (Seeman, P. (1972) Pharmacol. Rev. 24, 583–655) calculated that anesthetic agents exapnd membrane volume ten times more than the van der Waals volume of the agent alone. Their calculation was based on the assumption that the thickness of the erythrocyte membrane expands at the same rate as the surface area. However, recent data on bilayer membranes demonstrate that an expansion of membrane surface area is accompanied by a decrease in membrane thickness. A reinterpretation of their erythrocyte area expansion data using an appropriate contraction of membrane thickness suggests the volume in a membrane occupied by anesthetic molecules is approximately equal to their van der Waals volume.     

Extended acclimatization is required to eliminate stress effects of periodic blood-sampling procedures on vasoactive hormones and blood volume in beagle dogs

Important in all experimental animal studies is the need to control stress stimuli associated with environmental change and experimental procedures. As the stress response involves alterations in levels of vasoactive hormones, ensuing changes in cardiovascular parameters may confound experimental outcomes. Accordingly, we evaluated the duration required for dogs (n = 4) to acclimatized to frequent blood sampling that involved different procedures. On each sampling occasion during a 6-week period, dogs were removed from their pen to a laboratory area and blood was collected either by venepuncture (days 2, 15, 34, 41) for plasma renin activity (PRA), epinephrine (EPI), norepinephrine, aldosterone, insulin, and atrial natriuretic peptide, or by cannulation (dogs restrained in slings; days 1, 8, 14, 22, 30, 33, 37, 40) for determination of haematocrit (HCT) alone (days 1 to 22) or HCT with plasma volume (PV; days 30 to 40). PRA was higher on days 2 and 15 compared with days 34 and 41 and had decreased by up to 48% by the end of the study (day 41 vs day 15; mean/SEM: 1.18/0.27 vs 2.88/0.79 ng ANG I/ml/h, respectively). EPI showed a time-related decrease from days 2 to 34, during which mean values had decreased by 51% (mean/SEM: 279/29 vs 134/20.9 pg/ml for days 2 and 34, respectively), but appeared stable from then on. None of the other hormones showed any significant variability throughout the course of the study. HCT was relatively variable between days 1 to 22 but stabilized from day 30, after which all mean values were approximately 6% lower than those between days 1 and 8. We conclude that an acclimatization period of at least 4 weeks is required to eliminate stress-related effects in dogs associated with periodic blood sampling.     

Distribution of blood flow during exercise after blood volume expansion in swine

To study the distribution of blood flow after blood volume expansion, seven miniature swine ran at high speed (17.6-20 km/h, estimated to require 115% of maximal O2 uptake) on a motor-driven treadmill on two occasions: once during normovolemia and once after an acute 15% blood volume expansion (homologous whole blood). O2 uptake, cardiac output, heart rate, mean arterial pressure, and distribution of blood flow (with radiolabeled microspheres) were measured at the same time during each of the exercise bouts. Maximal heart rate was identical between conditions (mean 266); mean arterial pressure was elevated during the hypovolemic exercise (149 +/- 5 vs. 137 +/- 6 mmHg). Although cardiac output was higher and arterial O2 saturation was maintained during the hypervolemic condition (10.5 +/- 0.7 vs. 9.3 +/- 0.6 l/min), O2 uptake was not different (1.74 +/- 0.08 vs. 1.74 +/- 0.09 l/min). Mean blood flows to cardiac (+12.9%), locomotory (+9.8%), and respiratory (+7.5%) muscles were all elevated during hypervolemic exercise, while visceral and brain blood flows were unchanged. Calculated resistances to flow in skeletal and cardiac muscle were not different between conditions. Under the experimental conditions of this study, O2 uptake in the miniature swine was limited at the level of the muscles during hypervolemic exercise. The results also indicate that neither intrinsic contractile properties of the heart nor coronary blood flow limits myocardial performance during normovolemic exercise, because both the pumping capacity of the heart and the coronary blood flow were elevated in the hypervolemic condition.     

Chronic vasodilation produces plasma volume expansion and hemodilution in rats: consequences of decreased effective arterial blood volume

Plasma volume (PV) expansion is required for optimal pregnancy outcomes; however, the mechanisms responsible for sodium and water retention in pregnancy remain undefined. This study was designed to test the "arterial underfill hypothesis" of pregnancy which proposes that an enlarged vascular compartment (due to systemic vasodilation and shunting of blood to the placenta) results in renal sodium and water retention and PV expansion. We produced chronic vasodilation by 14 days administration of nifedipine (NIF; 10 mg·kg(-1)·day(-1)) or sodium nitrite (NaNO2; 70 mg·kg(-1)·day(-1)) to normal, nonpregnant female Sprague-Dawley rats. Mean arterial pressure, monitored by telemetry, was reduced by both NIF and NaNO2 but was unchanged in control rats. At day 14, vasodilator treatment lowered hematocrit and increased PV (determined by Evans blue dye dilution). Plasma osmolarity (Posm), sodium (PNa), and total protein concentrations all fell. These responses resemble the responses to normal pregnancy with hemodilution, marked PV expansion, and decreased Posm and PNa. Our previous work indicates a role of increased inner medullary phosphodiesterase-5 (PDE5) in the sodium retention of pregnancy. Here, we found that inner medullary PDE5A mRNA and protein expression were increased by both NIF and NaNO2 treatment vs. control; however, neither renal cortical nor aortic PDE5 expression was changed by vasodilator treatment. We suggest that a primary, persistent vasodilation drives increased inner medullary PDE5 expression which facilitates continual renal Na retention causing "refilling" of the vasculature and volume expansion.     

Intrinsic viscoelasticity of blood cell suspensions: effects of erythrocyte deformability

The intrinsic viscoelasticity of erythrocyte suspensions holds great potential for specifying the deformability of the individual, noninteracting cells in an oscillatory shear flow field. In order to extrapolate to zero cell concentration, the complex viscoelastic modulus was measured as a function of hematocrit using 2 Hertz oscillatory flow and a shear rate of 10/sec. This was done for both normal cells and cells with severely reduced deformability when hardened with glutaraldehyde. Suspension media were blood plasma, isotonic saline, and Dextran solutions. The real parts of the complex intrinsic visco-elasticities were obtained by an extrapolation using a regression fit to Huggins' equation. For normal cells in native plasma the values ranged from 1.7 to 2, increasing to the range 2.4 to 3.1 when the plasma was diluted with isotonic saline solution. For hardened cells the value obtained was near 3.5. These results are compared with theories for suspensions of both rigid and deformable particles. Several theories for deformable particles predict an increase in intrinsic viscoelasticity with increases in the ratio of the viscosity of the interior of the particle to that of the suspending medium. This ratio controls the balance between rotational and deformational response of the cell in the flow field. The trends of these theories were observed in the measurements.     

Altitude acclimatization and energy metabolic adaptations in skeletal muscle during exercise.

To determine whether the working muscle is able to sustain ATP homeostasis during a hypoxic insult and the mechanisms associated with energy metabolic adaptations during the acclimatization process, seven male subjects [23 +/- 2 (SE) yr, 72.2 +/- 1.6 kg] were given a prolonged exercise challenge (45 min) at sea level (SL), within 4 h after ascent to an altitude of 4,300 m (acute hypoxia, AH), and after 3 wk of sustained residence at 4,300 m (chronic hypoxia, CH). The prolonged cycle test conducted at the same absolute intensity and representing 51 +/- 1% of SL maximal aerobic power (VO2 max) and between 64 +/- 2 (AH) and 66 +/- 1% (CH) at altitude was performed without a reduction in ATP concentration in the working vastus lateralis regardless of condition. Compared with rest, exercise performed during AH resulted in a greater increase (P < 0.05) in muscle lactate concentration (5.11 +/- 0.68 to 22.3 +/- 6.1 mmol/kg dry wt) than exercise performed either at SL (5.88 +/- 0.85 to 11.5 +/- 3.1) or CH (5.99 +/- 0.88 to 12.4 +/- 2.1). These differences in lactate concentration have been shown to reflect differences in arterial lactate concentration and glycolysis (Brooks et al. J. Appl. Physiol. 71: 333-341, 1991). The reduction in glycolysis at least between AH and CH appears to be accompanied by a tighter metabolic control. During CH, free ADP was lower and the ATP-to-free ADP ratio was increased (P < 0.05) compared with AH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Human erythrocyte volume is linearly related to cell concentration in blood.

In 253 normal male subjects mean corpuscular volume decreases as red cell count increases. The result is statistically significant (p smaller than 0.005).