Is hypercalcemic diet a possible antidote to oral contraceptive-induced hypertension?

Administration of oral contraceptive (OC) has been associated with body fluid retention and in high doses over a long period, promotes hypertension. This present investigation tests the hypothesis that the dietary calcium supplementation increases salt and water excretion in OC (norgestre/ethinylestradiol) treated 32 female albino rats randomly distributed into four (1-4) groups of 8 rats each: Control, OC-treated, OC-treated+ Calcium diet fed and Calcium diet fed only respectively. OC was administered to the appropriate groups by gavage. Experimental diet contained 2.5% calcium supplement. Plasma and urinary [Na+] [K+] were evaluated after 8 weeks of experimentation by flame photometry and plasma [Ca2+] by colorimetric method. OC-treatment induced a significant fall in urinary [Na+]. Water excretion was significantly reduced in these animals (control, 3.1±0.56 Vs OC-treated rats, 1.47±0.16). OC-treated rats had significantly higher plasma [K+] compared to control rats. Calcium supplementation induced increases in plasma [Na+], [K+] and augmented urinary Na+ excretion (OC-treated + Ca2+ diet Vs OC-treated only). Compared with the control rats, high Ca2+ diet fed rats exhibited significant increases in plasma [Na+] and [K+] accompanied by significant decreases in urinary H20 excretion. These results strongly suggest that high dietary Ca2+ supplementation increases salt and water excretion in OC-treated rats and potentially moderates fluid retention and blood pressure in these animals, and may be of clinical significance in OC-induced abnormal fluid retention and perhaps OC-induced hypertension.Keywords: Hypercalcemic-diet, Oral contraceptive, Plasma electrolytes, Hypertension, Female-albino-rats.     

Estradiol-induced expression of N(+)-K(+)-ATPase catalytic isoforms in rat arteries: gender differences in activity mediated by nitric oxide donors

We tested the hypothesis that previously demonstrated gender differences in ACh-induced vascular relaxation could involve diverse Na(+)-K(+)-ATPase functions. We determined Na(+)-K(+)-ATPase by measuring arterial ouabain-sensitive 86Rb uptake in response to ACh. We found a significant increase of Na+ pump activity only in aortic rings from female rats (control 206 +/- 11 vs. 367 +/- 29 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.01). Ovariectomy eliminated sex differences in Na(+)-K(+)-ATPase function, and chronic in vivo hormone replacement with 17beta-estradiol restored the ACh effect on Na(+)-K(+)-ATPase. Because ACh acts by enhancing production of NO, we examined whether the NO donor sodium nitroprusside (SNP) mimics the action of ACh on Na(+)-K(+)-ATPase activity. SNP increased ouabain-sensitive 86Rb uptake in denuded female arteries (control 123 +/- 7 vs. 197 +/- 12 nmol 86Rb/K.min(-1).g wt tissue(-1); P < 0.05). Methylene blue (an inhibitor of guanylate cyclase) and KT-5823 (a cGMP-dependent kinase inhibitor) blocked the stimulatory action of SNP. Exposure of female thoracic aorta to the Na+/K+ pump inhibitor ouabain significantly decreased SNP-induced and ACh-mediated relaxation of aortic rings. At the molecular level, Western blot analysis of arterial tissue revealed significant gender differences in the relative abundance of catalytic isoforms of Na(+)-K(+)-ATPase. Female-derived aortas exhibited a greater proportion of alpha2-isoform (44%) compared with male-derived aortas. Furthermore, estradiol upregulated the expression of alpha2 mRNA in male arterial explants. Our results demonstrate that enhancement of ACh-induced relaxation observed in female rats may be in part explained by 1) NO-dependent increased Na(+)-K(+)-ATPase activity in female vascular tissue and 2) greater abundance of Na(+)-K(+)-ATPase alpha2-isoform in females.     

The effect of a low-protein diet in pregnancy on offspring renal calcium handling

Low birth weight humans and rats exposed to a low-protein diet in utero have reduced bone mineral content. Renal calcium loss during the period of rapid skeletal growth is associated with bone loss. Because young rats exposed to low protein display altered renal function, we tested the hypothesis that renal calcium excretion is perturbed in this model. Pregnant Wistar rats were fed isocalorific diets containing either 18% (control) or 9% (low) protein throughout gestation. Using standard renal clearance techniques, Western blotting for renal calcium transport proteins, and assays for Na(+)-K(+)-ATPase activity and serum calcitropic hormones, we characterized calcium handling in 4-wk-old male offspring. Histomorphometric analyses of femurs revealed a reduction in trabecular bone mass in low-protein rats. Renal calcium (control vs. low protein: 10.4 +/- 2.1 vs. 27.6 +/- 4.5 nmol x min(-1) x 100 g body wt(-1); P < 0.01) and sodium excretion were increased, but glomerular filtration rate was reduced in low-protein animals. Total plasma calcium was reduced in low-protein rats (P < 0.01), but ionized calcium, serum calcitropic hormone concentrations, and total body calcium did not differ. There was no significant change in plasma membrane Ca(2+)-ATPase pump, epithelial calcium channel, or calbindin-D(28K) expression in low-protein rat kidneys. However, Na(+)-K(+)-ATPase activity was 36% lower (P < 0.05) in low-protein rats. These data suggest that the hypercalciuria of low-protein rats arises through a reduction in passive calcium reabsorption in the proximal tubule rather than active distal tubule uptake. This may contribute to the reduction in bone mass observed in this model.     

Age-associated differential expression of Na(+)-K(+)-ATPase subunit isoforms in skeletal muscles of F-344/BN rats.

Skeletal muscle expresses multiple isoforms of the Na(+)-K(+)-ATPase. Their expression has been shown to be differentially regulated under pathophysiological conditions. In addition, previous studies suggest possible age-dependent alterations in Na(+)-K(+) pump function. The present study tests the hypothesis that advancing age is associated with altered Na(+)-K(+)-ATPase enzyme activity and isoform-specific changes in expression of the enzyme subunits. Red and white gastrocnemius (Gast) as well as soleus muscles of male Fischer 344/Brown Norway (F-344/BN) rats at 6, 18, and 30 mo of age were examined. Na(+)-K(+)-ATPase activity, measured by K(+)-stimulated 3-O-methylfluorescein phosphatase activity, increased by approximately 50% in a mixed Gast homogenate from 30-mo-old compared with 6- and 18-mo-old rats. Advancing age was associated with markedly increased alpha(1)- and beta(1)-subunit, and decreased alpha(2)- and beta(2)-subunit in red and white Gast. In soleus, there were similar changes in expression of alpha(1)- and alpha(2)-subunits, but levels of beta(1)-subunit were unchanged. Functional Na(+)-K(+)-ATPase units, measured by [(3)H]ouabain binding, undergo muscle-type specific changes. In red Gast, high-affinity ouabain-binding sites, which are a measure of alpha(2)-isozyme, increased in 30-mo-old rats despite decreased levels of alpha(2)-subunit. In white Gast, by contrast, decreased levels of alpha(2)-subunit were accompanied by decreased high-affinity ouabain-binding sites. Finally, patterns of expression of the four myosin heavy chain (MHC) isoforms (type I, IIA, IIX, and IIB) in these muscles were similar in the three age groups examined. We conclude that, in the skeletal muscles of F-344/BN rats, advancing age is associated with muscle type-specific alterations in Na(+)-K(+)-ATPase activity and patterns of expression of alpha- and beta-subunit isoforms. These changes apparently occurred without obvious shift in muscle fiber types, since expression of MHC isoforms remained unchanged. Some of the alterations occurred between middle-age (18 mo) and senescence (30 mo), and, therefore, may be attributed to aging of skeletal muscle.     

Characteristics of the K(+)-ion transport in the rat intestine following the use of natural zeolites as food additives

Effects of zeolites as a food supplement have been studied on Wistar rats both in vivo perfusion experiments in the jejunum and distal colon and Rb fluxes through intestinal wall in the Ussing chamber. It has been found that zeolites decrease the K+ absorption and stimulate K+ secretion in the gut. This effect was due to inhibition of the apical N(+)-K(+)-ATPase and ouabain-sensitive Na(+)-independent K(+)-ATPase as well as the activation of the basolateral N(+)-K(+)-ATPase.     

Mechanical stretching of alveolar epithelial cells increases Na(+)-K(+)-ATPase activity.

Alveolar epithelial cells effect edema clearance by transporting Na(+) and liquid out of the air spaces. Active Na(+) transport by the basolaterally located Na(+)-K(+)-ATPase is an important contributor to lung edema clearance. Because alveoli undergo cyclic stretch in vivo, we investigated the role of cyclic stretch in the regulation of Na(+)-K(+)-ATPase activity in alveolar epithelial cells. Using the Flexercell Strain Unit, we exposed a cell line of murine lung epithelial cells (MLE-12) to cyclic stretch (30 cycles/min). After 15 min of stretch (10% mean strain), there was no change in Na(+)-K(+)-ATPase activity, as assessed by (86)Rb(+) uptake. By 30 min and after 60 min, Na(+)-K(+)-ATPase activity was significantly increased. When cells were treated with amiloride to block amiloride-sensitive Na(+) entry into cells or when cells were treated with gadolinium to block stretch-activated, nonselective cation channels, there was no stimulation of Na(+)-K(+)-ATPase activity by cyclic stretch. Conversely, cells exposed to Nystatin, which increases Na(+) entry into cells, demonstrated increased Na(+)-K(+)-ATPase activity. The changes in Na(+)-K(+)-ATPase activity were paralleled by increased Na(+)-K(+)-ATPase protein in the basolateral membrane of MLE-12 cells. Thus, in MLE-12 cells, short-term cyclic stretch stimulates Na(+)-K(+)-ATPase activity, most likely by increasing intracellular Na(+) and by recruitment of Na(+)-K(+)-ATPase subunits from intracellular pools to the basolateral membrane.     

Regulation of renal Na(+),K(+)-ATPase and ouabain-sensitive H(+),K(+)-ATPase by the cyclic AMP-protein kinase A signal transduction pathway

We investigated the effect of the cyclic AMP-protein kinase A (PKA) signalling pathway on renal Na(+),K(+)-ATPase and ouabain-sensitive H(+),K(+)-ATPase. Male Wistar rats were anaesthetized and catheter was inserted through the femoral artery into the abdominal aorta proximally to the renal arteries for infusion of the investigated substances. Na(+),K(+)-ATPase activity was measured in the presence of Sch 28080 to block ouabain-sensitive H(+),K(+)-ATPase and improve specificity of the assay. Dibutyryl-cyclic AMP (db-cAMP) administered at a dose of 10(-7) mol/kg per min and 10(-6) mol/kg per min increased Na(+),K(+)-ATPase activity in the renal cortex by 34% and 42%, respectively, and decreased it in the renal medulla by 30% and 44%, respectively. db-cAMP infused at 10(-6) mol/kg per min increased the activity of cortical ouabain-sensitive H(+),K(+)-ATPase by 33%, and medullary ouabain-sensitive H(+),K(+)-ATPase by 30%. All the effects of db-cAMP were abolished by a specific inhibitor of protein kinase A, KT 5720. The stimulatory effect on ouabain-sensitive H(+),K(+)-ATPase and on cortical Na(+),K(+)-ATPase was also abolished by brefeldin A which inhibits the insertion of proteins into the plasma membranes, whereas the inhibitory effect on medullary Na(+),K(+)-ATPase was partially attenuated by 17-octadecynoic acid, an inhibitor of cytochrome p450-dependent arachidonate metabolism. We conclude that the cAMP-PKA pathway stimulates Na(+),K(+)-ATPase in the renal cortex as well as ouabain-sensitive H(+),K(+)-ATPase in the cortex and medulla by a mechanism requiring insertion of proteins into the plasma membrane. In contrast, medullary Na(+),K(+)-ATPase is inhibited by cAMP through a mechanism involving cytochrome p450-dependent arachidonate metabolites.     

Diet deficient in alpha-linolenic acid alters fatty acid composition and enzymatic properties of Na+, K+-ATPase isoenzymes of brain membranes in the adult rat

The effects of dietary (n-6)/(n-3) polyunsaturated fatty acid balance on fatty acid composition, ouabain inhibition, and Na(+) dependence of Na(+), K(+)-ATPase isoenzymes of whole brain membranes were studied in 60-day-old rats fed over two generations a diet either devoid of alpha-linolenic acid [18:3(n-3)] (sunflower oil diet) or rich in 18:3(n-3) (soybean oil diet). In the brain membranes, the sunflower oil diet led to a dramatic decrease in docosahexaenoic acid [22:6(n-3)] membrane content. The activities of Na(+), K(+)-ATPase isoenzymes were discriminated on the basis of their differential affinities for ouabain and their sensitivity to sodium concentration. The ouabain titration curve of Na(+), K(+)-ATPase activity displayed three inhibitory processes with markedly different affinity [i.e., low (alpha1), high (alpha2), and very high (alpha3)] for brain membranes of rats fed the sunflower oil diet, whereas the brain membranes of rats fed the soybean oil diet exhibited only two inhibitory processes, low (alpha1) and high (alpha2' = alpha2 + alpha3). Regardless of the diet, on the basis of the Na(+) dependence of Na(+), K(+)-ATPase activity, three isoenzymes were found: alpha1 form displaying an affinity 1.5- to 2-fold higher that of than alpha2 and 3-fold higher that of alpha3. In rats fed the sunflower oil diet, alpha2 isoenzyme exhibited higher affinity for sodium (Ka = 8.8 mmol/L) than that of rats fed the soybean oil diet (Ka = 11.7 mmol/L). These results suggest that the membrane lipid environment modulates the functional properties of Na(+), K(+)-ATPase isoenzymes of high ouabain affinity (alpha2).     

Regulation of fish gill Na(+)-K(+)-ATPase by selective sulfatide-enriched raft partitioning during seawater adaptation

Na(+)-K(+)-ATPase is arguably the most important enzyme in the animal cell plasma membrane, but the role of the membrane in its regulation is poorly understood. We investigated the relationship between Na(+)-K(+)-ATPase and membrane microdomains or "lipid rafts" enriched in sulfatide (sulfogalactosylceramide/SGC), a glycosphingolipid implicated as a cofactor for this enzyme, in the basolateral membrane of rainbow trout gill epithelium. Our studies demonstrated that when trout adapt to seawater (33 ppt), Na(+)-K(+)-ATPase relocates to these structures. Arylsulfatase-induced desulfation of basolateral membrane SGC prevented this relocation and significantly reduced Na(+)-K(+)-ATPase activity in seawater but not freshwater trout. We contend that Na(+)-K(+)-ATPase partitions into SGC-enriched rafts to help facilitate the up-regulation of its activity during seawater adaptation. We also suggest that differential partitioning of Na(+)-K(+)-ATPase between these novel SGC-enriched regulatory platforms results in two distinct, physiological Na(+) transport modes. In addition, we extend the working definition of cholesterol-dependent raft integrity to structural dependence on the sulfate moiety of SGC in this membrane.     

Aldosterone-mediated regulation of Na+, K(+)-ATPase gene expression in adult and neonatal rat cardiocytes.

By altering the Na+/K+ electrochemical gradient, Na+,K(+)-ATPase activity profoundly influences cardiac cell excitability and contractility. The recent finding of mineralocorticoid hormone receptors in the heart implies that Na+,K(+)-ATPase gene expression, and hence cardiac function, is regulated by aldosterone, a corticosteroid hormone associated with certain forms of hypertension and classically involved in regulating Na+,K(+)-ATPase gene expression and transepithelial Na+ transport in tissues such as the kidney. The regulation by aldosterone of the major cardiac Na+,K(+)-ATPase isoform genes, alpha-1 and beta-1, were studied in adult and neonatal rat ventricular cardiocytes grown in defined serum-free media. In both cell types, aldosterone-induced a rapid and sustained 3-fold induction in alpha-1 mRNA accumulation within 6 h. beta-1 mRNA was similarly induced. alpha-1 mRNA induction occurred over the physiological range with an EC50 of 1-2 nM, consistent with binding of aldosterone to the high affinity mineralocorticoid hormone receptor. In adult cardiocytes, this was associated with a 36% increase in alpha subunit protein accumulation and an increase in Na(+)-K(+)-ATPase transport activity. Aldosterone did not alter the 3-h half-life of alpha-1 mRNA, indicating an induction of alpha-1 mRNA synthesis. Aldosterone-dependent alpha-1 mRNA accumulation was not blocked by the protein synthesis inhibitor cycloheximide, whereas amiloride inhibited both an aldosterone-dependent increase in intracellular Na+ [Na+]i) and alpha-1 mRNA accumulation. This demonstrates that aldosterone directly stimulates Na+,K(+)-ATPase alpha-1 subunit mRNA synthesis and protein accumulation in cardiac cells throughout development and suggests that the heart is a mineralocorticoid-responsive organ. An early increase in [Na+]i may be a proximal event in the mediation of the hormone effect.     

Renal Na+-K+-ATPase in weanling and adult spontaneously hypertensive rats

The interrelationships among plasma renin activity (PRA, ng AI/ml plasma/hr), aldosterone concentration (ng%), and renal Na+-K+-ATPase activity (mumole PO4/mg protein/hr) were studied in 9 weanling normotensive spontaneously hypertensive rats (SHR), 9 adult hypertensive SHR, and 9 weanling and 9 adult normotensive Wistar-Kyoto rats (WKY). All groups were placed on a normal (0.4% sodium) diet. PRA and plasma aldosterone, measured in samples drawn from the ether-anesthetized rat, were higher in weanling SHR (15.2 +/- 2.0, 37 +/- 4.2) than in WKY. PRA measured in samples collected from a separate group of unanesthetized weanling SHR was also greater than in age-matched WKY. In adult SHR, PRA (6.1 +/- 0.9) and plasma aldosterone (20.0 +/- 2.7) were decreased. During the weanling period Na+-K+-ATPase activity in SHR was not only greater than in age-matched WKY but was also increased compared to adult normotensive and hypertensive rats (137 +/- 9 weanling SHR, 89 +/- 7 weanling WKY, 73 +/- 11 adult SHR, 84 +/- 17 adult WKY). Thus, during the weanling period the renin-angiotensin-aldosterone (R-A-A) system and renal Na+-K+-ATPase activity are activated in SHR. The elevation of Na+-K+-ATPase activity may be due to increased aldosterone levels. It was noted, however, that plasma aldosterone was similar in adult WKY and weanling SHR, while Na+-K+-ATPase activity was higher in SHR. These findings involving R-A-A and renal Na+-K+-ATPase activity prior to the elevation of blood pressure suggest that the kidneys may play a role in the initiation of hypertension in SHR.     

大鼠单根近端肾小管Na+-K+-ATPase活性测定方法的改进

本研究旨在对Doucet等报道的定量检测大鼠单根近端肾小管Na^＋-K^＋-ATPase活性方法进行改进。取经过Ⅱ型胶原酶消化的大鼠肾脏皮质组织,在体视显微镜下手工分离单根近端肾小管,并测量其长度,经低渗和冻融处理后与[γ-^32P]ATP共同孵育,液闪法检测从[γ-^32P]ATP解离出的^32Pi,采用修正后的公式计算Na^＋-K^＋-ATPase活性。改良法与Doucet等的方法比较,测定单根近端肾小管Na^＋-K^＋-ATPase活性无显著性差异（P〉0．05）。改进后的方法节省试剂,操作简便、省时。     

Reduced activity of muscle Na(+)-K(+)-ATPase after prolonged running in rats.

The purpose of this study was to investigate the hypothesis that Na(+)-K(+)-ATPase activity is reduced in muscle of different fiber composition after a single session of aerobic exercise in rats. In one experiment, untrained female Sprague-Dawley rats (weight 275 +/- 21 g; means +/- SE; n = 30) were run (Run) on a treadmill at 21 m/min and 8% grade until fatigue, or to a maximum of 2 h, which served as control (Con), or performed an additional 45 min of low-intensity exercise at 10 m/min (Run+). In a second experiment, utilizing rats of similar characteristics (weight 258 +/- 18 g; n = 32), Run was followed by passive recovery (Rec). Directly after exercise, rats were anesthetized, and tissue was extracted from Soleus (Sol), red vastus lateralis (RV), white vastus lateralis (WV), and extensor digitorum longus (EDL) and frozen for later analysis. 3-O-methylfluorescein phosphatase activity (3-O-MFPase) was determined as an indicator of Na(+)-K(+)-ATPase activity, and glycogen depletion identified recruitment of each muscle during exercise. 3-O-MFPase was decreased (P < 0.05) at Run+ by an average of 12% from Con in all muscles (P < 0.05). No difference was found between Con and Run. Glycogen was lower (P < 0.05) by 65, 57, 44, and 33% (Sol, EDL, RV, and WV, respectively) at Run, and there was no further depletion during the continued low-intensity exercise period. No differences in Na(+)-K(+)-ATPase activity was observed between Con and Rec. The results of this study indicate that inactivation of Na(+)-K(+)-ATPase can be induced by aerobic exercise in a volume-dependent manner and that the inactivation that occurs is not specific to muscles of different fiber-type composition. Inactivation of Na(+)-K(+)-ATPase suggests intrinsic structural modifications by mechanisms that are unclear.     

Fatigue depresses maximal in vitro skeletal muscle Na(+)-K(+)-ATPase activity in untrained and trained individuals.

This study investigated whether fatiguing dynamic exercise depresses maximal in vitro Na(+)-K(+)-ATPase activity and whether any depression is attenuated with chronic training. Eight untrained (UT), eight resistance-trained (RT), and eight endurance-trained (ET) subjects performed a quadriceps fatigue test, comprising 50 maximal isokinetic contractions (180 degrees /s, 0.5 Hz). Muscle biopsies (vastus lateralis) were taken before and immediately after exercise and were analyzed for maximal in vitro Na(+)-K(+)-ATPase (K(+)-stimulated 3-O-methylfluoroscein phosphatase) activity. Resting samples were analyzed for [(3)H]ouabain binding site content, which was 16.6 and 18.3% higher (P < 0.05) in ET than RT and UT, respectively (UT 311 +/- 41, RT 302 +/- 52, ET 357 +/- 29 pmol/g wet wt). 3-O-methylfluoroscein phosphatase activity was depressed at fatigue by -13.8 +/- 4.1% (P < 0.05), with no differences between groups (UT -13 +/- 4, RT -9 +/- 6, ET -22 +/- 6%). During incremental exercise, ET had a lower ratio of rise in plasma K(+) concentration to work than UT (P < 0.05) and tended (P = 0.09) to be lower than RT (UT 18.5 +/- 2.3, RT 16.2 +/- 2.2, ET 11.8 +/- 0.4 nmol. l(-1). J(-1)). In conclusion, maximal in vitro Na(+)-K(+)-ATPase activity was depressed with fatigue, regardless of training state, suggesting that this may be an important determinant of fatigue.     

Effect of increased dietary calcium on body weight, food and water intake in oral contraceptive treated female rats

The effects of high calcium diet on body weight in OC treated rats are unknown. This study therefore investigated the effect of increasing dietary calcium from 0.9% to 2.5% on body weight, food ingestion, water intake, heart weight index and renal weight index in female Sprague-Dawley rats treated with a combination of OC steroids (ethinyloestradiol + norgestrel). The rats were assigned into three groups of average of 11 rats each; control, OC-treated and OC + Calcium – treated groups and administered orally for 10 weeks. Food and water intake, body weight, cardiac weight index, left ventricular weight index, renal weight index and serum calcium level were determined. The result shows that OC treated rats had significantly lower serum calcium concentration, body weight gain, food, water and calcium intake than those of the control rats. The OC + Calcium – treated rat had significantly higher serum calcium concentration, food, water and calcium intake but significantly lower body weight than those of the OC - treated rats. OC + Calcium - treated rats had significantly higher water intake, calcium intake and significantly lower body weight and food intake when compared with the control rats. Cardiac weight index and renal weight index was comparable in all groups. In conclusion, combined OC-induced reduction in weight gain might be associated with inhibition of the feeding center and consequent inhibition of the thirst center. Co-administration of dietary calcium augmented the reduction in weight gain seen in OC-treated rats probably by further suppression of the feeding and thirst centers.     

Effect of hydroxyl radical on Na(+)-K(+)-ATPase activity of the brain microsomal membranes.

Sphingomyelin liposomes and brain microsomes were oxidized by exposure to hydrogen peroxide and ferrous ion. Lipid peroxidation were measured by the formation of thiobarbituric acid- reactive substances (TBAR). Hydroxyl radical was detected using the spin- trapping technique. Incubation of sphingomyelin liposomes with H2O2-Fe2+ resulted in an increase in the formation of TBAR. Na(+)-K(+)-ATPase activity was markedly inhibited and the SH group content decreased during incubation of microsomes in the presence of H2O2-Fe2+. Sodium ferulate effectively inhibited TBAR formation, protected Na(+)-K(+)-ATPase activity and prevented the oxidative modification of SH groups. Spin-trapping experiments showed that sodium ferulate effectively scavenged the hydroxyl radicals.     

Effects of sprint training on extrarenal potassium regulation with intense exercise in Type 1 diabetes.

Effects of sprint training on plasma K+ concentration ([K+]) regulation during intense exercise and on muscle Na+-K+-ATPase were investigated in subjects with Type 1 diabetes mellitus (T1D) under real-life conditions and in nondiabetic subjects (CON). Eight subjects with T1D and seven CON undertook 7 wk of sprint cycling training. Before training, subjects cycled to exhaustion at 130% peak O2 uptake. After training, identical work was performed. Arterialized venous blood was drawn at rest, during exercise, and at recovery and analyzed for plasma glucose, [K+], Na+ concentration ([Na+]), catecholamines, insulin, and glucagon. A vastus lateralis biopsy was obtained before and after training and assayed for Na+-K+-ATPase content ([3H]ouabain binding). Pretraining, Na+-K+-ATPase content and the rise in plasma [K+] ([K+]) during maximal exercise were similar in T1D and CON. However, after 60 min of recovery in T1D, plasma [K+], glucose, and glucagon/insulin were higher and plasma [Na+] was lower than in CON. Training increased Na+-K+-ATPase content and reduced [K+] in both groups (P < 0.05). These variables were correlated in CON (r = -0.65, P < 0.05) but not in T1D. This study showed first that mildly hypoinsulinemic subjects with T1D can safely undertake intense exercise with respect to K+ regulation; however, elevated [K+] will ensue in recovery unless insulin is administered. Second, sprint training improved K+ regulation during intense exercise in both T1D and CON groups; however, the lack of correlation between plasma delta[K+] and Na+-K+-ATPase content in T1D may indicate different relative contributions of K+-regulatory mechanisms.     

Influence of chronic alterations of salt intake and aging on the kinetic of red cell Na+ and K+ transport in Sprague-Dawley rats

The kinetics of Na+ and K+ (Rb)+ transport mediated by the Na(+)-K+ pump and Na(+)-K+ cotransport system (assessed as a function of Rb+o and Na+i) as well as the magnitude of cation leaks were determined in red cells of young male rats subjected to chronic salt deprivation or salt loading (0.1% and 8% NaCl diet). These salt intake alterations induced moderate kinetic changes of the Na(+)-K+ pump which did not result in significant changes of ouabain-sensitive (OS) Rb+ uptake or Na+ net extrusion at in vivo Na+i and K+o concentrations because a decreased affinity for Na+i in salt-loaded animals was compensated by an increased maximal transport rate. High furosemide-sensitive (FS) Rb+ uptake in red cells of salt-deprived rats was caused by an increase of both the maximal transport rate and the affinity for Rb+o. Cation leaks were also higher in salt-deprived than in salt-loaded rats. In three age groups of rats fed a 1% NaCl diet FS Rb+ uptake (but not FS Na+ net uptake) rose with age due to an increasing maximal transport rate whereas the affinity of the cotransport system for Rbo+ did not change. The age-dependent changes in the kinetics of the Na(+)-K+ pump resulted in a slight decrease of OS Rb+ uptake with age that was not paralleled by corresponding Na+ net extrusion. No major age-related changes of cation leaks were found. Thus some intrinsic properties of red cell transport systems can be altered by salt intake and aging.     

Adenosine triphosphatase activity in sciatic nerve tissue of streptozocin-induced diabetic rats with and without high dietary sucrose: effect of aldose reductase inhibitors.

The ability of aldose reductase inhibitors to prevent the decline in neural Na+,K(+)-ATPase activity in diabetic rats has not been confirmed by all laboratories. In this study, the efficacy of two structurally different aldose reductase inhibitors was evaluated under different experimental conditions. Na+,K(+)-ATPase activity was measured in sciatic nerves from streptozocin-induced diabetic rats fed normal rodent chow or a chow supplemented with 68% sucrose. Nerve homogenates from chow-fed rats were prepared with a Dounce tissue grinder, whereas homogenates from the sucrose-fed rats were prepared with an Ultra-Turrax disperser. In the chow-fed rats, 4 weeks of untreated diabetes resulted in an increase in neural sorbitol and fructose, a decrease in myoinositol, and a 54% decline in Na+,K(+)-ATPase activity. Sorbinil administration (20 mg/kg/day) completely prevented the rise in sorbitol and fructose and the depletion of myoinositol, but did not prevent the decline in Na+,K(+)-ATPase activity. In diabetic rats fed the sucrose diet for 4, 6, and 8 weeks, the neural sorbitol and fructose levels were elevated, the myoinositol concentration declined, and the Na+,K(+)-ATPase activity was 26 to 28% below the control. Prevention or intervention treatment with sorbinil (20 mg/kg/day) or tolrestat (50 mg/kg/day) for 4 to 6 weeks prevented the alterations in sorbitol, fructose, and myoinositol, and also prevented the decline in Na+,K(+)-ATPase activity. In conclusion, prevention and intervention therapy with aldose reductase inhibitors prevented the decline in Na+,K(+)-ATPase in sciatic nerves of sucrose-fed streptozocin-diabetic rats that were homogenized with an Ultra-Turrax disperser, but not in sciatic nerves from streptozocin-diabetic rats fed normal rodent chow that were homogenized with a Dounce tissue grinder. These findings indicate that the assessment of aldose reductase inhibitor efficacy is dramatically affected by the type of nerve preparation assayed and/or the diet.     

Effect of high-NaCl or high-KCl diet on hepatic Na+- and K+-receptor sensitivity and NKCC1 expression in rats

We previously reported that the bumetanide-sensitive Na(+)-K(+)-2Cl- cotransporter (NKCC1) is involved in the hepatic Na+ and K+ sensor mechanism. In the present study, we examined the effects of a high-NaCl or high-KCl diet on hepatic Na+ and K+ receptor sensitivity and NKCC1 expression in the liver of Sprague-Dawley rats. RT-PCR and Western blots were used to measure NKCC1 mRNA and protein expression, respectively. Infusion of hypertonic NaCl or isotonic KCl + NaCl solutions into the portal vein increased hepatic afferent nerve activity (HANA) in a Na+ or K+ dose-dependent manner. After 4 wk on a high-NaCl or high-KCl diet, HANA responses were attenuated compared with animals fed a normal diet, and NKCC1 expression was reduced. These results show that a high-NaCl or high-KCl diet decreases NKCC1 expression in the liver, and it might cause a reduction in hepatic Na(+)- and K(+)-receptor sensitivity.