Irreversible Changes in Rat Erythrocyte Na+ Transport Systems with Progesterone and Estradiol Administration

In order to test whether alterations in Na⁺ transport systems occurring in women when the hormonal status is disturbed such as in pregnancy, under contraceptive or estradiol therapy are a direct result of hormonal action on these transport systems, Na⁺, K⁺-pump Na⁺, K⁺ outward cotransport and passive Na⁺ permeability were measured in erythrocytes of ovariectomized rats receiving estradiol or progesterone. No significant changes in Na⁺, K⁺-pump were observed in either conditions. Conversely, progesterone was found to decrease Na⁺, K⁺-cotransport and estradiol to increase this system, whereas both steroids increased passive Na⁺ permeability.     

Inverse relationship between colonic (Na+ + K+)-ATPase activity and degree of mucosal inflammation in inflammatory bowel disease

In inflammatory bowel disease (IBD), mucosal damage and loss of colonic function are regarded as major consequences of inflammation. Decreased colonic (Na⁺ + K⁺)-ATPase activities with diminished reabsorption of sodium and water have been found in active stages of ulcerative colitis. In this study, we report an inverse relationship between colonic (Na⁺ + K⁺)-ATPase activity and the degree of mucosal inflammation in 19 patients with IBD of mild to moderate disease activity. Various macroscopic and histologic types of mucosal lesions were differently associated with the (Na⁺ + K⁺)-ATPase activities. 5-nucleotidase activity was not associated with the degree of mucosal inflammation or the kind of macroscopic or histologic lesions. Our findings support the view that, in contrast to 5-nucleotidase, (Na⁺ + K⁺)-ATPase activity may better reflect the severity of mucosal damage and the degree of inflammation in IBD.     

High-protein diet: A barrier to the nephroprotective effects of sodium-glucose co-transporter-2 inhibitors?

Glomerular hyperfiltration is a common finding in patients with diabetes and poor glycaemic control; whole-kidney hyperfiltration, with glomerular filtration rate (GFR) values above normal, should be differentiated from single nephron hyperfiltration, consequent to nephron loss and compensatory hyperfiltration of the remnant nephrons. This is the result of an imbalance between the vascular tone of the afferent and efferent arterioles. Hormonal influences and/or an impaired tubuloglomerular feedback (TGF) system, because of excessive sodium (Na⁺) and glucose reabsorption in the proximal tubule, contribute to determine hyperfiltration. Sodium-glucose co-transporter-2 inhibitors (SGLT2is), by decreasing Na⁺ reabsorption and increasing the delivery of Na⁺ to the macula densa, lead to normalization of TGF, and, consequently, decrease GFR (both whole and single nephron). High-protein diets are popular among patients with type 1 and type 2 diabetes; importantly, 80% of the amino acids are also reabsorbed in the proximal tubule of the nephron and are transported by symporters that use the electro-chemical gradient of Na⁺. Indeed, an acute protein load is associated with increased Na⁺ reabsorption and an increase in GFR. Here, we hypothesize that high-protein diets, by increasing Na⁺ reabsorption and GFR, may offset the positive renal effects of SGLT2is.     

Altered Arachidonic Acid Metabolism Contributes to the Failure of Dopamine to Inhibit Na+, K+-ATPase in Kidney of Spontaneously Hypertensive Rats

Dopamine decreases tubular sodium reabsorption in part by inhibition of Na⁺, K⁺-ATPase activity in renal proximal tubules. The signaling mechanism involved in dopamine-mediated inhibition of Na⁺, K⁺-ATPase is known to be defective in spontaneously hypertensive animals. The present study was designed to evaluate the role of phospholipase A2 (PLA2) and its metabolic pathway in dopamine-induced inhibition of Na⁺, K⁺-ATPase in renal proximal tubules from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Renal proximal tubular suspensions were prepared and Na⁺, K⁺-ATPase activity was measured as ouabain-sensitive adenosine triphosphate hydrolysis. Dopamine inhibited Na⁺,K⁺-ATPase activity in a concentration (1 nM - 10 μM)-dependent manner in WKY rats while it failed to inhibit the enzyme activity in SHR. Dopamine (10μM)-induced inhibition of Na⁺,K⁺-ATPase activity in WKY rats was significantly blocked by mepacrine (10 μM), a PLA2 inhibitor, suggesting the involvement of PLA2 in dopamine-mediated inhibition of Na⁺,K⁺-ATPase. Arachidonic acid (a product released by PLA2 action) inhibited Na⁺,K⁺-ATPase in a concentration-dependent (1-100 μM) manner in WKY rats while the inhibition in SHR was significantly attenuated (IC₅₀: 7.5 and 80 μM in WKY rats and SHR, respectively). Furthermore, lower concentrations of arachidonic acid stimulated (30% at 1 μM) Na⁺,K⁺-ATPase activity in SHR. This suggests a defect in the metabolism of arachidonic acid in SHR. Proadifen (10 μM), an inhibitor of cytochrome P-450 monoxygenase (an arachidonic acid metabolizing enzyme) significantly blocked the inhibition produced by arachidonic acid in WKY rats and abolished the difference in arachidonic acid inhibition of Na⁺,K⁺-ATPase between WKY rats and SHR. These data suggest that PLA2 is involved in dopamine-induced inhibition of Na⁺,K⁺-ATPase and altered arachidonic acid metabolism may contribute to reduced dopaminergic inhibition of Na⁺,K⁺-ATPase activity in spontaneously hypertensive rats.     

Basis of Rise in Intracellular Sodium in Airway Hyperresponsiveness and Asthma

The aim of this study was to investigate the basis of disturbances in sodium transport in asthma and in airway hyperresponsiveness without symptoms of asthma (asymptomatic AHR). We measured the intracellular sodium (Na_i); activity of Na⁺/K⁺-ATPase in unstimulated cells (resting activity) and in cell homogenate under optimal conditions (maximal activity); and sodium influx, in mixed leukocytes of 15 normal subjects, 12 subjects with asymptomatic AHR, and 26 asthmatics with or without active symptoms. Resting Na⁺/K⁺-ATPase activity was the same as sodium influx, consistent with homeostasis. Compared with normal subjects, those with asymptomatic AHR or asthma with controlled symptoms had a twofold increase in sodium influx and Na_i. Symptomatic asthmatics also had a twofold increase in sodium influx but a fourfold elevation of Na_i. Maximal Na⁺/K⁺-ATPase activity was reduced by half in symptomatic asthmatics compared with normal subjects. The reduction of maximal Na⁺/K⁺-ATPase activity was associated with a significant decrease in ATP turnover per Na⁺/K⁺-ATPase molecule but not number of Na⁺/K⁺-ATPase molecules per cell. In summary, airway hyperresponsiveness with or without asthma is associated with increased sodium influx and Na in leukocytes. Resting activity of Na⁺/K⁺-ATPase is also increased as a compensatory response to the increased sodium influx, but it is achieved at the expense of higher Na_i. Symptomatic asthma is additionally associated with reduction in maximal activity of Na⁺/K⁺-ATPase, resulting in reduced capacity to handle the increase in sodium influx and consequent severe elevations in Na_i.     

Changes of extracellular Na+, K+, Ca2+ and H+ of the ischemic myocardium in pigs

Summary In open-chest pigs during severe myocardial ischemia [K⁺]e, [Ca²⁺]e and [H⁺]e increase, [Na⁺]e increases transiently reaching control values after 30 min. Extracellular osmolality of the ischemic area increases due to an H₂O-shift from the ECS to the ICS. The increase of [Na⁺]e and [Ca²⁺]e must be explained by the shrinkage of the ECS due to the H₂O-shift. The increase of [Ca²⁺]e is additionally caused by the decrease of pHe. The increase of [K⁺]e is mainly caused by the release of K⁺ from the ICS. The changes of [K⁺]e and [K⁺]i cause a decrease of the membrane potential to a range in which slow response potentials and re-entry excitations can occur. The increase of [K⁺e therefore seems to be a major factor to cause early post-ischemic arrhythmias.Supported by Deutsche Forschungsgemeinschaft, SFB 68, A 7     

Insulin does not regulate vascular smooth muscle Na+, K+-ATPase activity in rabbit aorta

Summary To determine whether insulin regulates vascular smooth muscle Na⁺, K⁺-ATPase activity and if impaired insulin stimulation of vascular smooth muscle Na⁺, K⁺-ATPase activity could be a cause of increased vascular reactivity to norepinephrine and angiotensin II in diabetic states, the effects of insulin on Na⁺, K⁺-ATPase activity were examined in normal rabbit aortic intima-media incubated with normal plasma glucose and myo-inositol levels for 30 min. Insulin at 100 U/ml (600 pmol/l) had no effect on Na⁺, K⁺-ATPase activity. At 250 U/ml it caused a 4.2±0.8% increase, and at 500 U/ml insulin caused a 17.7±1.4% increase in Na⁺, K⁺-ATPase activity that was completely inhibited by amiloride (1 mmol/l). Human insulin-like growth factor I (600 pmol/l) caused an 18.0±1.0% increase in Na⁺, K⁺-ATPase activity that was inhibited by amiloride. Insulin does not regulate (stimulate) aortic vascular smooth muscle Na⁺, K⁺-ATPase activity. Supraphysiological insulin concentrations, probably acting through an insulin-like growth factor I receptor, stimulate Na⁺/H⁺ exchange in aortic vascular smooth muscle and cause small secondary increases in Na⁺, K⁺-ATPase activity. In aortic intima-media incubated with normal plasma glucose and myo-inositol levels, endogenously released adenosine stimulates and maintains a component of resting Na⁺, K⁺-ATPase activity and stimulates acute increases in activity when norepinephrine (1 mol/l) or angiotensin II (100 nmol/l) is added. These adenosine-stimulated components of Na⁺, K⁺-ATPase activity are selectively inhibited when the medium glucose is raised to 30 mmol/l during a 30-min equilibration and 30-min incubation. Insulin (100 U/ml) added during the incubation had no effect on the alterations in Na⁺, K⁺-ATPase activity induced by glucose at an elevated plasma level. Impaired insulin stimulation of vascular smooth muscle Na⁺, K⁺-ATPase activity is not a possible cause for alterations in vascular reactivity in diabetes.     

Erythrocyte Na+/K+-ATPase and Membrane and Serum Lipid Profiles: As Related to Alcohol,Body Mass Index and Blood Pressure

Erythrocyte Na⁺/K⁺-pump activities have been measured in hypertensives, alcohol consumers and obese persons, but the results have been variously reported as decreased, increased or unchanged. We analyzed the relationships between erythrocyte Na⁺/K⁺-ATPase activities and the membrane and serum lipid profiles in 83 middle-aged men, to clarify the reasons for these inconsistencies. Increases in erythrocyte Na⁺/K⁺-ATPase activity related closely to decreases in cholesterol to phospholipid (C/P) ratio of the erythrocyte membrane. Decreases in the C/P ratio in turn related closely to elevations of serum triglycerides (TG) with increasing body mass index, and weakly to the volume of alcohol consumed. Thus, erythrocyte Na⁺/K⁺-ATPase activities depend largely on the membrane and serum lipid profiles as related to body weight and alcohol consumption.     

Urinary acidification capacity in the elderly

Renal acidification in 18 healthy elderly subjects was studied using furosemide 80 mg orally, as a substance to stimulate H⁺ and K⁺ secretion by enhancing Na⁺ delivery and transport in the cortical collecting duct. In five subjects, group 2 (n=5), the furosemide failed to lower urinary pH below 5.5, but resulted in an increase in potassium excretion and decrease in net acid excretion. These effects were obliterated by amiloride, a drug which decreases transtubular epithelial voltage (lumen-negative) in the cortical collecting tubule (CCT) by blocking Na⁺ reabsorption. The serum bicarbonate in this group was normal, and they were considered as suffering from incomplete distal renal tubular acidosis (IC-DRTA). In group 1 (n=13), the furosemide resulted in a fall in urinary pH below 5.5, and in an increase in net acid excretion. Our results show that in a subgroup of elderly subjects there is a proton pump defect located in the cortical collecting duct, and that the elderly are susceptible to metabolic acidosis during stress conditions or high protein diet.     

Hyperinsulinaemia and Na+, K+ -ATPase activity in thyrotoxic periodic paralysis

OBJECTIVE Thyrotoxic periodic paralysis (TPP) usually follows a heavy carbohydrate meal and this may be explained by hyperinsulinaemia stimulating Na⁺, K⁺ -ATPase activity. To clarify this the effect of glucose load on serum insulin concentration and platelet Na⁺, K⁺ -ATPase activity In thyrotoxic periodic paralysis (TPP) was examined. DESIGN In all subjects a standard 75-g glucose tolerance test was done and blood samples were taken at 0, 1 and 2 hours. SUBJECTS Twenty-five healthy controls (8 M and 17 F), 17 uncomplicated thyrotoxic patients (7M and 10 F), 15 TPP patients who presented with paralysis and 4 TPP patients after treatment with antithyrold drugs. MEASUREMENTS Plasma glucose was measured by the glucose oxidase method, serum insulin by radioimmunoassay and platelet Na⁺, K⁺ -ATPase by the release of phosphate from ATP. RESULTS TPP patients showed glucose intolerance (area under the curve (AUC) 16·5 ± 4·4 (mean ± SD) In TPP compared to 12·9 ± 4·5 In controls (P < 0·01) and hyperinsulinaemia (AUC 189·6 ±100·6 vs 98·5 ±53·4, P < 0·001). In uncomplicated thyrotoxicosis the results were similar to that in healthy controls. Platelet Na⁺, K⁺ -ATPase were significantly higher in thyrotoxic patients compared to controls and In TPP patients were even higher. Ingestion of glucose increased platelet Na⁺, K⁺ -ATPase in all groups. AUC for platelet Na⁺, K⁺ -ATPase in TPP patients were significantly higher than in uncomplicated thyrotoxicosis (601 ±99·3 vs 482 ± 109·4, P < 0·01) or healthy controls (320 ± 107·3). In the 4 TPP patients studied after antithyroid treatment the results were similar to healthy controls. CONCLUSION Patients with thyrotoxic periodic paralysis have hyperinsulinaemia and this is accompanied by higher Na⁺, K⁺-ATPase activity.     

Apparent Upregulation of Na+, K+ Pump Sites in SHR Skeletal Muscle with Reduced Transport Capacity

Slow-twitch, oxidative skeletal muscles in SHR exhibit several physiological defects, including a reduced ability to maintain force during high frequency repetitive stimulation (1). Muscle fatigue may be produced by one of a variety of factors acting at different levels of the neuromuscular system. Several lines of evidence, however, suggest that SHR soleus fatigues more rapidly than WKY soleus because SHR muscles allow more K⁺ to accumulate in the extracellular space during repetitive muscle activity. An increase in extracellular K⁺ can lead to a failure in the generation or conduction of muscle action potentials. Comparison of the compound action potentials recorded from SHR and WKY muscles during repetitive stimulation provided evidence for a decrease in excitability of SHR soleus. Since the K⁺ released from muscle fibers during exercise is returned to the fiber principally via the activity of the Na⁺, K⁺ pump, the increase in extracellular K⁺ in SHR muscle may reflect a decrease in pump capacity. Measurements including intracellular K⁺ and Na⁺ content at rest, the level of hyperpolarization produced by the addition of epinephrine and insulin to SHR soleus and the post-exercise recovery of resting membrane potentials all appear to indicate that Na⁺, K⁺ pump capacity is reduced in SHR soleus muscles. Nonetheless, ouabain binding studies show a significantly greater number of pump sites in SHR muscles. The data suggest that Na⁺ pump activity is decreased in SHR soleus muscles without an apparent reduction in either the number of pump sites or in pump binding affinity.     

Decreased nitric oxide synthase activity in platelets from IDDM and NIDDM patients

Summary Nitric oxide (NO) produced by platelet nitric oxide synthase (NOS) inhibits platelet activation by increased cytoplasmic cGMP levels. The aim of this study was to investigate platelet NOS activity in insulin-dependent (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM), which are characterized by enhanced platelet activation. HbA_{1 c} levels, platelet NOS and platelet membrane Na⁺/K⁺ ATPase activity were determined in 19 IDDM patients, 21 NIDDM patients and 31 healthy control subjects. NOS activity was measured by a spectrophotometric method based on NO-dependent oxidation of oxyhaemoglobin to met-haemoglobin. Na⁺/K⁺ ATPase activity was measured by the method of Kitao and Hattori. Both NOS and Na⁺/K⁺ ATPase activity were significantly reduced in diabetic subjects compared with control subjects. NOS showed a significant negative relation with HbA_{1 c} levels and a positive relation with Na⁺/K⁺ ATPase activity in diabetic patients. It is hypothesized that the decreased NOS activity might play a role in the pathogenesis of diabetic vascular complications. [Diabetologia (1998) 41: 101–104] Received: 30 June 1997 and in revised form: 3 September 1997     

Studies in avian adrenal steroid function: I: Survival and mineral balance following adrenalectomy in domestic ducks (Anas platyrhynchos L.)

Surgically adrenalectomised ducks survive 117 ± 17 hr (n = 8), withouth NaCl or steroid therapy. Na⁺ and K⁺ metabolism were studied in chronically restrained adrenalectomised or sham-operated birds for up to 5 days following surgery: sham-operated birds remained in Na⁺ balance by matching renal-cloacal Na⁺ retention to intake rates, but during the first 2–3 postoperative days adrenalectomised birds were unable to reduce cloacal fluid Na⁺ concentrations. The resultant natriuresis (despite reduced cloacal fluid flow rates) and the low feeding rate brought adrenalectomised birds into severely negative Na⁺ balance. All birds showed negative K⁺ balance initially after surgery. 3–5 Days after adrenalectomy, birds recovered normal Na⁺ and K⁺ balance in the absence of residual adrenal tissue, probably due to steroid-independent rectal ion transport. Normalised ion balances were at a high turnover rate in sham-operated birds, but at a low rate in adrenalectomised birds. However, the latter group showed persistent severe hyponatraemia and kyperkalaemia until death.     

Myocardial (Na+k+)-Atpase Activity in Daul Salt-Sensitive and Resistant Rats

Vascular (Na⁺K⁺)-punp activity (ouabain-sensitive ⁵⁶Rb⁺uptake) and myocardial (Na⁺K⁺)-ATPase activity are reduced in. animals with various forms of low renin, experimental hypertersion. On the other hand, vascular (Na⁺, K⁺)-puinp activity is increased in Dahl salt-sensitive relative to resistant rats (a genetic model of hypertension), regardless of salt intake or blood pressure and it is also increased in Dahl salt-sensitive rats on high salt (3% NaCl) relative to low salt (0.4% NaCl) diets. It has been suggested that this increase in vascular (Na⁺K⁺)-pump activity may be secondary to an increase in the vascular sarcolemmal permeability to Na⁺in these salt-sensitive rats. In the present study, (Na⁺K⁺)-ATPase activity of left ventricular microsomal fractions, was increased in Dahl salt-sensitive relative to resistant rats on low salt diets; however, this difference disappeared when these salt-sensitive and resistant rats were placed on high salt diets. In contrast, mvocardial (Na⁺K⁺)-ATPase activity was decrease in Dahl salt-sensitive rats on high relative to low salt diets. Evidence that this decrease in (Na⁺K⁺)-ATPase activity is not secondary to myocardial hypertrophy in the hypertensive salt-sensitive rats, and mechanisms by which decreased cardiovascular (Na⁺K⁺)-pump activity, increased sarcolemmal permeability or both, might contribute to elevated blood pressure, are discussed.     

Enhanced growth and Na+/H+ antiport activity response to serum in cultured fibroblasts of diabetic patients with nephropathy

To explore whether elevated red blood cell sodium-lithium countertransport in type 1 (insulin-dependent) diabetic patients with nephropathy is related to the physiological Na⁺/H⁺ antiport activity, we measured the activity of this antiport in serially passaged cultured skin fibroblasts from insulin-dependent diabetic patients with and without nephropathy and from non-diabetic controls. Na⁺/H⁺ antiport activity (measured as the rate of amiloride-sensitive Na⁺ influx) was significantly elevated in patients with nephropathy compared with patients without nephropathy and normal controls (13.35±3.8 vs 8.54±2.0 vs 7.33±2.3 nmol Na⁺/mg protein per min;P<0.006 andP<0.001 respectively). This raised activity in patients with nephropathy was due to an increasedV _max for extracellular Na⁺.K _m values were similar in the three groups. Amiloride-sensitive Na⁺ influx was also higher in cells under baseline conditions and after serum stimulation from patients with nephropathy. Intracellular pH values were significantly higher, both during active proliferation and after 10 min of exposure to serum, in cells from patients with nephropathy compared with patients without nephropathy and normal controls. Serum-stimulated incorporation of [³H]thymidine into DNA was greater in patients with nephropathy than in the other two groups. These data in cultured fibroblasts suggest that intrinsic abnormalities in cell function, independently of the metabolic disturbances of diabetes, are a feature of diabetic patients who develop nephropathy.     

Homocysteine alters glutamate uptake and Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase activity and oxidative status in rats hippocampus: protection by vitamin C

In the present study we investigate the effect of homocysteine on glutamate uptake, Na⁺,K⁺-ATPase, enzymatic antioxidant defenses, as well as reactive species levels in hippocampus of rats. The influence of vitamin C, a classic antioxidant, on the effects elicited by homocysteine was also tested. Results showed that chronic hyperhomocysteinemia decreased glutamate uptake and the activities of Na⁺,K⁺-ATPase, catalase and superoxide dismutase in hippocampus of rats. Reactive species levels were increased by chronic homocysteine administration. Concomitant administration of vitamin C significantly prevented these alterations caused by homocysteine. According to our results, it seems possible to suggest that the reduction in glutamate uptake and Na⁺,K⁺-ATPase activity may be mediated by oxidative stress, since vitamin C prevented these effects. We suggest that the administration of antioxidants should be considered as an adjuvant therapy to specific diet in homocystinuria.     

NO levels in diabetes mellitus: Effects of l-NAME and insulin on LCAT,Na+/K+ ATPase activity and lipid profile

ObjectivesDiabetes mellitus (DM) is a chronic disease and one of the most important health problems. Several factors may be responsible for the complications of diabetes mellitus including alterations in the activities of sodium–potassium adenosine triphosphatase (Na⁺/K⁺ ATPase) and lecithin:cholesterol acyltransferase (LCAT) and also levels of nitric oxide (NO). We have investigated the effects of alterations in serum NO levels on activities of erythrocyte membran Na/K ATPase and serum LCAT enzymes.Materials and methodsThe experiments were performed on male rats divided into four groups: group 1, control (standart diet); group 2, diabetic control (single dose of 65 mg/kg of streptozotocin (STZ), i.p); group 3, STZ + insulin (8 IU/kg/day s.c.); group 4 (STZ + l-NAME 5 mg/kg/day orally).ResultStreptozotocin-induced diabetic rats, showed a significant increase in blood glucose and serum cholesterol (C) and triglyceride (TG). Compared to the control group with diabetic group plasma LCAT concentrations and erythrocyte membrane Na⁺/K⁺ ATPase were found to be decreased. Activities of Na⁺/K⁺ ATPase and serum NO level were decreased with the administration of l-NAME. We observed that insulin was ameliorated in all parameters.ConclusionsSerum NO levels is related to erythrocyte membrane Na⁺/K⁺ ATPase activity. But serum NO levels did not affect the plasma LCAT activity and serum lipid profiles.     

Alteration of Na+ homeostasis as a critical step in the development of irreversible hepatocyte injury after adenosine triphosphate depletion

The exposure of isolated hepatocytes to the redox-cycling quinone menadione caused an early loss of mitochondrial membrane potential, adenosine triphosphate (ATP) depletion, and decreased intracellular pH. These alterations were followed by an increase in intracellular Na⁺ and, ultimately, cell death. If HCO₃⁻ was omitted from the incubation buffer, or the hepatocytes were incubated in an acidic medium (pH 6.5) the accumulation of Na⁺ was markedly reduced. Inhibition of the Na⁺/H⁺ exchanger and of the Na⁺/HC0₃⁻ cotransporter by, respectively, amiloride and 4,4′-di-isothiocyano-2,2′-disulfonic acid stilbene (DIDS) suppressed the initial Na⁺ influx but did not prevent subsequent Na⁺ accumulation, because amiloride and DIDS inhibited the Na⁺/K⁺ pump. The omission of HCO₃⁻ from the extracellular medium or the incubation in acidic conditions also prevented menadione toxicity, without interfering with the loss of mitochondrial membrane potential and with ATP depletion. A similar protection was evident when hepatocytes were incubated with menadione in a medium without Na⁺. The preservation of adequate levels of ATP by supplementing hepatocytes with fructose allowed the initial Na⁺ load to be recovered and provided partial protection against menadione toxicity. These effects were suppressed if Na⁺/K⁺-ATPase was inhibited with ouabain. Taken together, these results indicated that the activation of the Na⁺/HCO₃⁻ cotransporter and of the Na⁺/K⁺ exchanger in response to the decrease of intracellular pH stimulated an enhanced influx of Na⁺. When the activity of the Na⁺/K⁺ pump was not able to control Na⁺ levels because of ATP depletion, such an uncontrolled Na⁺ influx precipitated irreversible injury and caused hepatocyte death.     

Acute effects of digoxin on plasma aldosterone and cortisol in monkeys

Digoxin, a cardiac glycoside, is used to increase cardiac contractility via inhibition of Na⁺/K⁺-adenosinetriphosphatase (ATPase) and increase intracellular calcium in congestive heart failure. Inhibitory effects of digoxin have been demonstrated on the biosynthesis of gonadal hormones and adrenal glucocorticoids in rats. However, acute effects of digoxin on levels of adrenal corticosteroid hormones in the primates in vivo are uncertain. Therefore, we test the hypothesis that a single injection of digoxin decreases the secretion of aldosterone and cortisol in monkeys. An intravenous injection of digoxin (1 μg/kg) inhibited basal and adrenocorticotropin (ACTH)- or KCl-stimulated aldosterone release in monkeys. Furthermore, digoxin induced a decrease in ACTH- and KCl-stimulated cortisol release. Administration of digoxin did not alter plasma concentrations of Na⁺ and K⁺. Ouabain, a selective inhibitor of Na⁺/K⁺-ATPase, did not affect ACTH- or KCl-stimulated aldosterone and cortisol release. These results revealed that injection of digoxin induced an inhibitory effect on aldosterone and cortisol secretion in monkeys. Because ouabain did not affect levels of plasma aldosterone or cortisol, we suggest that (1) the Na⁺/K⁺-ATPase pathway may not be involved in the mechanism of action of digoxin on aldosterone or cortisol secretion in monkeys and/or (2) the Na⁺/K⁺-ATPase is more sensitive to digoxin than to ouabain in monkeys.     

Supplementation with vitamins E plus C or soy isoflavones in ovariectomized rats: effect on the activities of Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>-ATPase and cholinesterases

Since a previous study demonstrated that ovariectomized rats present an activation of Na⁺, K⁺-ATPase and acetylcholinesterase (AChE) activities, in the present study we investigated the influence of vitamins E plus C or soy isoflavones on the effects elicited by ovariectomy on the activities of these enzyme in hippocampus of ovariectomized rats. We also determined the effect of the same compounds on the reduction of serum butyrylcholinesterase (BuChE) activity caused by ovariectomy. Female adult Wistar rats were assigned to one of the following groups: sham (submitted to surgery without removal of the ovaries) and ovariectomized. Seven days after surgery, animals were treated for 30 days with a single daily intraperitoneous injection of vitamins E (40 mg/kg) plus C (100 mg/kg) or saline (control). In another set of experiments, the rats were fed for 30 days on a special diet with soy protein or a standard diet with casein (control). Rats were sacrificed after treatments and the hippocampus was dissected and serum was separated. Data demonstrate that vitamins E plus C reversed the activation of Na⁺, K⁺-ATPase and AChE in hippocampus of ovariectomized rats. Conversely, soy protein supplementation reversed the increase of AChE activity, but not of Na⁺, K⁺-ATPase activity, caused by ovariectomized group. Neither treatment was able to reverse the reduction of serum BuChE activity. Furthermore, treatments with vitamins E plus C or soy were unable to reverse the decrease in estradiol levels caused by ovariectomy. Our findings show that the treatment with vitamins E plus C significantly reversed the effect of ovariectomy on hippocampal Na⁺, K⁺-ATPase and AChE activities. However, a soy diet that was rich in isoflavones was able to reverse just the increase of AChE. Neither treatment altered the reduction in serum BuChE activity. Taken together, these vitamins and soy may have a protective role against the possible brain dysfunction observed in some menopause women. Vitamins E plus C and soy isoflavones may be a good alternative as a novel therapeutic strategy.