Increase In Na-K ATPase Activity Research Articles

7342 Thyrotoxic Periodic Paralysis

Abstract Disclosure: G. Arora: None. Case presentation: A 40 year old male with no significant past medical history presented to the emergency department with diffuse body weakness for one day. On the night prior to admission, his thighs started getting sore which in a matter of a few hours, progressed to weakness involving his entire body. He was unable to flex his hips, shoulders, and neck. He was unable to get up or move without assistance. He was found to have an irregular heartbeat two weeks prior to admission and had undergone a thyroid ultrasound which showed inflammation of the thyroid gland. He was not started on any new medications. He endorsed fatigue, palpitations, neck swelling, and 45 lbs unintentional weight loss over 6 months. No fever, chills, vision changes, congestion, chest pain, shortness of breath, cough, tingling, numbness or weakness. He denied alcohol or drug use. Physical examination was notable for blood pressure 151/80 mm Hg, heart rate 120 bpm, enlarged thyroid gland tender to palpation, and muscle weakness (motor strength 3/5 in flexors and extensors of hips and knees). Labs were notable for K 2.3 (3.5 - 5.1 mmol/L), ALP 218 (32 - 91 U/L), TSH <0.010 (0.400 - 4.300 mcIU/mL), Free T4 3.5 (0.6 - 1.6 ng/dL), CK 608 (49 - 397 U/L). Urine toxicology was negative. MRI spine did not show any acute abnormality except for thyromegaly. He received potassium supplementation which led to symptomatic improvement and was admitted to medical floor. Further tests revealed: TSI 39.50 (<=0.54 IU/L), TSH receptor antibody 26 (<=1.75 IU/L), thyroid microsomal antibody 773.3 (0.0 - 9.0 IU/mL), anti-thyroglobulin antibody 4 (<4 IU/mL). Thyroid ultrasound showed an enlarged, heterogenous, hypervascular thyroid without any nodules. He was started on Propranolol and Propylthiouracil, which led to symptom resolution and he was discharged. Discussion: Thyrotoxic periodic paralysis (TPP) is a rare muscle disorder, belonging to the family of diseases called channelopathies. Thyroid hormone increases tissue responsiveness to beta-adrenergic stimulation, which increases Na-K ATPase activity on the skeletal muscle membrane driving potassium into cells. This leads to hyperpolarization of the muscle membrane and relative inexcitability of the muscle fibers, especially in the presence of a trigger such as provocation with exercise, fasting state or a high carbohydrate meal (insulin stimulates Na-K ATPase pump). Furthermore, more than 95% of TPP cases occur in males. This predominance is due to androgen-induced Na-K ATPase sensitization, more pronounced hyperinsulinemia, comparatively higher sympathetic and catecholamine-induced Na-K ATPase activity and higher muscle mass in males. Given the life-threatening association of severe hypokalemia, TPP should be considered in all patients presenting with acute painless muscle weakness. Presentation: 6/3/2024

Flowerpot method for rapid eye movement sleep deprivation does not induce stress as defined by elevated serum corticosterone level in rats

Flowerpot method of rapid eye movement sleep (REMS) deprivation (REMSD) has been most extensively used in experiments to decipher the functions of REMS. The most common but serious criticism of this method has been presumed stress experienced by the experimental animals. The lack of systematic studies with appropriate controls to resolve this issue prompted this study. We have compared serum corticosterone levels as a marker of stress in male rats under REMSD by the flowerpot method and multiple types of control conditions. Additionally, to maintain consistency and uniformity of REMSD among groups, in the same rats, we estimated brain Na-K ATPase activity, which has been consistently reported to increase upon REMSD. The most effective method was one rat in single- or multiple-platforms set-up in a pool because it significantly increased Na-K ATPase activity without elevating serum corticosterone level. More than one rat in multiple platform set-up was ineffective and must be avoided. Also, large platform- and recovery-controls must be carried out simultaneously to rule out non-specific confounding effects.

Mechanism of noradrenaline-induced α1-adrenoceptor mediated regulation of Na-K ATPase subunit expression in Neuro-2a cells

Rapid eye movement sleep (REMS) plays an important role in maintaining brain excitability by regulating noradrenaline (NA) level and Na-K ATPase activity. We showed earlier that REMS deprivation (REMSD) associated elevated NA increased neuronal, while decreased glial Na-K ATPase activity. However, our knowledge was insufficient on how the REMSD-associated effect is sustained particularly under chronic condition. Using Neuro-2a cells as a model, we investigated the molecular mechanism of NA-induced increase in mRNA expression of Na-K ATPase subunit and the enzyme activity. The cells were treated with NA in the presence or absence of either α1- or β-adrenoceptor (AR) antagonists, Ca++-channel blocker or SERCA-inhibitor, and PKA or PKC inhibitor. We observed that NA acting on α1-AR increased Na-K ATPase activity and mRNA expression of the catalytic α1- and α3-Na-K ATPase subunits in the Neuro-2a cells. Further, PLC and PKC mediated modulation of intracellular Ca++ played a critical role in inducing the mRNA expression. On the other hand NA, acting on β-AR up-regulated expression of the regulatory β1-subunit of Na-K ATPase. The involvement of SP1 as well as phospho-CREB transcription factors in the NA-mediated increased expression of various subunit isoforms was established. The results of this study along with that of earlier reports support our proposed working model of NA-induced increase in mRNA expression of specific Na-K ATPase subunit leading to increased Na-K ATPase activity. The findings help us understand the molecular mechanism of NA-induced increased brain excitability, for example, upon REMSD including under chronic condition.

Rapid Eye Movement Sleep Deprivation Associated Increase in Na-K ATPase Activity in the Rat Brain is Due to Noradrenaline Induced α1-Adrenoceptor Mediated Increased α-Subunit of the Enzyme.

Rapid eye movement sleep (REMS) modulates Na-K ATPase activity and maintains brain excitability. REMS deprivation (REMSD)-associated increased Na-K ATPase activity is mediated by noradrenaline (NA) acting on α1-adrenoceptor (AR) in the brain. It was shown that NA-induced increased Na-K ATPase activity was due to allosteric modulation as well as increased turnover of the enzyme. Although the former has been studied in detail, our understanding on the latter was lacking, which we have studied. Male Wistar rats were REMS deprived for 4-days by classical flower-pot method; suitable control experiments were conducted. In another set, α1-AR antagonist prazosin (PRZ) was i.p. injected 48 h REMSD onward. At the end of experiments rats were sacrificed by cervical dislocation and brains were removed. Synaptosomes prepared from the brains were used to estimate Na-K ATPase activity as well as protein expressions of different isoforms of the enzyme subunits using western blot. REMSD significantly increased synaptosomal Na-K ATPase activity and that was due to differential increase in the expressions of α1-, α2- and α3-isoforms, but not that of β1- and β2-isoforms. PRZ reduced the REMSD-induced increased Na-K ATPase activity and protein expressions. We also observed that the increased Na-K ATPase subunit expression was not due to enhanced mRNA synthesis, which suggests the possibility of post-transcriptional regulation. Thus, the findings suggest that REMSD-associated increased Na-K ATPase activity is due to elevated level of α-subunit of the enzyme and that is induced by NA acting on α1-AR mediated mRNA-stabilization.

INCREASED AEROBIC GLYCOLYSIS THROUGH β2 STIMULATION IS A COMMON MECHANISM INVOLVED IN LACTATE FORMATION DURING SHOCK STATES

During septic shock, muscle produces lactate by way of an exaggerated NaK-adenosine triphosphatase (ATPase)-stimulated aerobic glycolysis associated with epinephrine stimulation possibly through beta2 adrenoreceptor involvement. It therefore seems logical that a proportion of hyperlactatemia in low cardiac output states would be also related to this mechanism. Thus, in low-flow and normal-to-high-flow models of shock, we investigate (1) whether muscle produces lactate and (2) whether muscle lactate production is linked to beta2 adrenergic stimulation and Na+K+-ATPase. We locally modulated the adrenergic pathway and Na+K+-ATPase activity in male Wistar rats' skeletal muscle using microdialysis with nonselective and selective beta blockers and ouabain in different models of rodent shock (endotoxin, peritonitis, and hemorrhage). Blood flow at the probe site was evaluated by ethanol clearance. We measured the difference between muscle lactate and blood lactate concentration, with a positive gradient indicating muscle lactate or pyruvate production. Epinephrine levels were elevated in all shock groups. All models were associated with hypotension and marked hyperlactatemia. Muscle lactate concentrations were consistently higher than arterial levels, with a mean gradient of 2.5+/-0.3 in endotoxic shock, 2.1+/-0.2 mM in peritonitis group, and 0.9+/-0.2 mM in hemorrhagic shock (P<0.05 for all groups). Muscle pyruvate concentrations were also always higher than arterial levels, with a mean gradient of 260+/-40 microM in endotoxic shock, 210+/-30 microM in peritonitis group, and 90+/-10 microM in hemorrhagic shock (P<0.05 for all groups). Despite a decrease in blood flow, lactate formation was decreased by all the pharmacological agents studied irrespective of shock mechanism. This demonstrates that lactate production during shock states is related, at least in part, to increased NaK-ATPase activity under beta2 stimulation. In shock state associated with a reduced or maintained blood flow, an important proportion of muscle lactate release is regulated by a beta2 receptor stimulation and not secondary to a reduced oxygen availability.

Nanomolar concentrations of ouabain stimulate Na‐K ATPase through sodium hydrogen exchanger‐1 (NHE1) dependent mechanism.

Recent investigations have shown increased Na‐H exchanger activity and plasma levels of endogenous cardiotonic glycosides, such as ouabain in spontaneously hypertensive rats. At high concentrations, ouabain inhibits pump activity, and at lower concentrations, it increases pump activity and induces cell proliferation. Stimulation of NHE1 and Na‐K ATPase activity involve protein kinase B (AKT), suggesting that both NHE1 and Na‐K ATPase are mediated by the same proteins. We hypothesize that the activity of NHE1 and Na‐K ATPase are linked. In the present study we aim to 1) determine the role of activation of NHE1 in ouabain‐sensitive stimulation of Na‐K ATPase, 2) determine if NHE1 and Na‐K ATPase association increases when cells were treated with NH4Cl or ouabain in various kidney proximal tubule cell lines (OK, HK2, HK5, and HK11). Our data suggests that NH4Cl stimulation of NHE1 increases ouabain sensitive 86Rb uptake in all cell lines examined.Treatment with ethylisopropylamiloride (EIPA) a NHE1 specific inhibitor decreased Na‐K ATPase activity in HK5 and HK11 cells and prevented nanomolar ouabain‐stimulated Na‐K ATPase activity in OK cells. Immunoblot analysis indicated that NH4Cl increased membrane expression of NHE1 and Na‐K ATPase in OK and HK11 cells. Surprisingly, treatment with EIPA alone increased membrane expression of NHE1 and Na‐K ATPase. The reason for increased presence of these proteins in the membrane is unknown, however, tyrosine phosphorylation of the catalytic subunit of Na‐K ATPase, believed to be an indication of Na‐K ATPase activation, is decreased under these same conditions. These results suggest that activation of NHE1 is critical for ouabain stimulated increase in Na‐K ATPase activity, and that upon activation, NHE1 and Na‐K ATPase associate, perhaps to form a signalosome.

Diabetic nephropathy: nitric oxide and renal medullary hypoxia

DIABETES, SPECIFICALLY DIABETIC nephropathy, is the most frequent cause of end-stage renal disease (ESRD) in developed countries (10). Classically, studies into the mechanisms underlying diabetic nephropathy have focused on glomerular injury and the development of albuminuria; however, changes in tubulointerstitial structure and function are also evident even during the early stages in diabetes (3, 4, 11, 13, 14, 16). Changes in proximal tubule structure consistent with hypertrophy (increases in cell height, tubule diameter, and length) are a prominent component of diabetic renal hypertrophy, with other nephron segments also displaying changes in tubule length (13, 14). There is evidence of altered renal handling of electrolytes, including Na, and increased renal Na-KATPase (NKA) activity has been widely reported in diabetes. The changes in NKA activity accompanying type 1 diabetes mellitus coincide with, and thus may play a role in, the development of hypertrophy. On the other hand, as NKAmediated ion transport is the major consumer of metabolic energy in the kidney, the early and pronounced increase in tubular NKA activity in diabetes has been proposed to represent an important adaptive response to the osmotic diuresis (4, 16) and/or the chronic increase in filtered Na load. Upregulation of NKA activity is particularly evident in the outer medulla (3, 4, 16), where low blood flow limits O2 supply despite high O2 consumption coupled with reabsorptive Na transport. As O2 extraction is almost maximal under normal conditions in the outer medulla, the increased NKA activity linked to increased Na transport during diabetes is accompanied by reduced PO2 in this region that normally exists near the brink of hypoxia. Thus diabetes would promote chronic hypoxia, which may be a common pathway leading to ESRD (8). In the healthy kidney, the renal medulla has high concentrations of nitric oxide (NO) (18). Reduced NO bioavailability has been shown to result in increased O2 consumption and, therefore, increased sodium reabsorption in the renal medulla (2, 5). Diabetes is known to be a condition of oxidative stress and reduced NO bioavailability. Little information is available in the literature pertaining to the status of NO and O2 availability in the renal medulla during diabetes. Palm and colleagues (12) have begun to unravel the complex mechanisms involved in the interrelationship between reduced NO bioavailability and hypoxia in the renal medulla in the early stages of diabetes. Palm et al. (12) report that reduced renal medullary NO levels in diabetes are due to decreased plasma L-arginine and unrelated to diabetes-induced oxidative stress, while the reduction in medullary PO2 was restored by L-arginine administration or antioxidant treatment. The authors also observed that the O2 availability in both normal and diabetic rats was independent of blood flow alterations. These observations underscore the potential importance of diabetes-induced renal metabolic alterations and their functional consequences. At physiological concentrations, NO inhibits the mitochondrial enzyme cytochrome c oxidase (complex IV) in competi

Role of norepinephrine in the regulation of rapid eye movement sleep.

Sleep and wakefulness are instinctive behaviours that are present across the animal species. Rapid eye movement (REM) sleep is a unique biological phenomenon expressed during sleep. It evolved about 300 million years ago and is noticed in the more evolved animal species. Although it has been objectively identified in its present characteristic form about half a century ago, the mechanics of how REM is generated, and what happens upon its loss are not known. Nevertheless, extensive research has shown that norepinephrine plays a crucial role in its regulation. The present knowledge that has been reviewed in this manuscript suggests that neurons in the brain stem are responsible for controlling this state and presence of excess norepinephrine in the brain does not allow its generation. Furthermore, REM sleep loss increases levels of norepinephrine in the brain that affects several factors including an increase in Na-K ATPase activity. It has been argued that such increased norepinephrine is ultimately responsible for REM sleep deprivation, associated disturbances in at least some of the physiological conditions leading to alteration in behavioural expression and settling into pathological conditions.

Uncompetitive stimulation of rat brain Na-K ATPase activity by rapid eye movement sleep deprivation

Rapid eye movement sleep deprivation is associated with an increase in Na-K ATPase activity. In order to understand the possible biochemical mechanism of this increase, the kinetics of Na-K ATPase was studied. Although the enzyme activity increased after the deprivation, the catalytic efficiency of the enzyme remained unaltered. The rapid eye movement sleep deprivation increased both the V max and the K m suggesting an uncompetitive stimulation of the enzyme. While increase in norepinephrine resulted in an increased V max, that of calcium increased the K m. Since an increase in norepinephrine has been suggested after deprivation, the increased V max is attributed to increased norepinephrine level following deprivation. However, since rapid eye movement sleep deprivation is reported to be associated with a decrease in calcium levels, the increase in K m following deprivation may be attributed to changes in factor(s) other than calcium.

Insulin stimulates transepithelial sodium transport by activation of a protein phosphatase that increases Na-K ATPase activity in endometrial epithelial cells.

The objective of this study was to investigate the effects of insulin and insulin-like growth factor I on transepithelial Na(+) transport across porcine glandular endometrial epithelial cells grown in primary culture. Insulin and insulin-like growth factor I acutely stimulated Na(+) transport two- to threefold by increasing Na(+)-K(+) ATPase transport activity and basolateral membrane K(+) conductance without increasing the apical membrane amiloride-sensitive Na(+) conductance. Long-term exposure to insulin for 4 d resulted in enhanced Na(+) absorption with a further increase in Na(+)-K(+) ATPase transport activity and an increase in apical membrane amiloride-sensitive Na(+) conductance. The effect of insulin on the Na(+)-K(+) ATPase was the result of an increase in V(max) for extracellular K(+) and intracellular Na(+), and an increase in affinity of the pump for Na(+). Immunohistochemical localization along with Western blot analysis of cultured porcine endometrial epithelial cells revealed the presence of alpha-1 and alpha-2 isoforms, but not the alpha-3 isoform of Na(+)-K(+) ATPase, which did not change in the presence of insulin. Insulin-stimulated Na(+) transport was inhibited by hydroxy-2-naphthalenylmethylphosphonic acid tris-acetoxymethyl ester [HNMPA-(AM)(3)], a specific inhibitor of insulin receptor tyrosine kinase activity, suggesting that the regulation of Na(+) transport by insulin involves receptor autophosphorylation. Pretreatment with wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase as well as okadaic acid and calyculin A, inhibitors of protein phosphatase activity, also blocked the insulin-stimulated increase in short circuit and pump currents, suggesting that activation of phosphatidylinositol 3-kinase and subsequent stimulation of a protein phosphatase mediates the action of insulin on Na(+)-K(+) ATPase activation.

Norepinephrine induced alpha-adrenoceptor mediated increase in rat brain Na-K ATPase activity is dependent on calcium ion

It has been reported that norepinephrine increases Na-K ATPase activity by acting on α-1 adrenoceptors. The mechanism of such an increase was investigated. The norepinephrine induced increase in synaptosomal Na-K ATPase activity was prevented by pretreating the rat brain homogenate with either EDTA, a divalent cation chelator or prazosin, an α-1 adrenoceptor blocker. The norepinephrine and EGTA increased the Na-K ATPase activity in the synaptosome prepared from rat brain homogenate untreated with EDTA. The EGTA was ineffective in stimulating the enzyme activity if the synaptosome was prepared from homogenate treated with norepinephrine. However, the EGTA was effective in increasing the enzyme activity if the synaptosome was prepared from the homogenate treated with norepinephrine in the presence of prazosin. Thus, norepinephrine did not increase the Na-K ATPase activity in the presence of EDTA or α-1 adrenoceptor blocker. Similarly, the Ca ++ chelator, EGTA, could not increase the enzyme activity if the homogenate was pretreated with norepinephrine alone. However, if norpeinephrine action was blocked by α-1 antagonist prazosin, EGTA increased the enzyme activity possibly by chelation of Ca ++. Further, chlorotetracycline fluorescence study showed that norepinephrine removes membrane bound Ca ++. Thus, it is likely that norepinephrine acts on adrenoceptors and removes membrane bound Ca ++ and thereby increases the Na-K ATPase activity in the synaptosome.

Possible mechanism of rapid eye movement sleep deprivation induced increase in Na-K ATPase activity.

Rapid eye movement sleep deprivation increases Na-K ATPase activity and decreases aminergic neuronal firing rate as well as norepinephrine degrading enzyme, monoamine oxidase, activity. On the other hand, norepinephrine is known to increase Na-K ATPase activity. Hence, this study was conducted to find if the deprivation induced increase in Na-K ATPase activity is mediated by norepinephrine. Rapid eye movement sleep deprived rats were injected with either alpha-1 or beta adrenoceptor antagonist or alpha-2 adrenoceptor agonist and after 8 h the Na-K ATPase activity of the brain was estimated. In an attempt to simulate in vivo conditions, norepinephrine was added to an in vitro brain homogenate preparation in the presence or absence of alpha or beta adrenoceptor blockers and the enzyme activity was estimated. The results showed that the enzyme activity was decreased by alpha-1 antagonist as well as by alpha-2 agonist treatment in in vivo preparations. Norepinephrine increased enzyme activity in the in vitro preparation and the increase was prevented by the alpha-1 antagonist. The results of this study suggest that rapid eye movement sleep deprivation induced increase in Na-K ATPase activity may be mediated by norepinephrine acting on either alpha-1 and/or alpha-2 receptors.

Effect of maternal hyperglycemia on NaK ATPase activity in fetal rat kidney.

The effect of moderate hyperglycemia on renal ATP production and ATPase activity of rat fetus was investigated using the experimental procedure of maternal continuous infusion of glucose during the last 5 days of gestation. Glucose-infused mothers and their fetuses showed a high level of glycemia (8.8 and 5.5 mM, respectively) and a high level of insulinemia (3 times higher than in controls). No change in either ATP or ADP concentration was detectable but an increase in NaK ATPase activity occurred without any change in Mg ATPase activity. These modifications should be the result of an enhanced Na/glucose cotransport leading to an enhanced extrusion of Na at the basolateral membrane. These results indicate that immature kidney is able to increase NaK ATPase activity to maintain Na homeostasis.

PHOSPHOLIPASE-C AND NA-K ATPASE ACTIVATION BY CYCLOSPORINE AND FK506 IN LLC-PK1, CELLS

Enhanced Na+ and water reabsorption by proximal tubular epithelial cells plays an important role in the development of systemic hypertension associated with cyclosporine immunosuppression. Since such Na+ reabsorption is subserved by sodium-potassium adenosine triphosphatase (Na-K ATPase), the current study compared the acute effects of hydrocortisone (H), cyclosporine, and FK506 on cultured LLC-PK1 cell viability and on Na-K ATPase activity. Phospholipase-C (PL-C) activity was also investigated because of its possible regulatory effect on Na-K ATPase activity. Culture medium containing low (5 nM, 4.1 ng/ml) or high (10 nM) concentrations of FK506 plus cyclosporine at 415 microM (500 ng/ml) resulted in cell death, whereas cyclosporine concentrations of 83 microM plus 5 nM or 10 nM FK506, or isolated use of the two drugs at high dosages, did not affect cell viability. As compared with controls, cyclosporine increased Na-K ATPase activity, particularly with addition of H (P less than 0.01). In contrast, FK506 reduced the specific activity of both PL-cyclosporine and Na-K ATPase (P less than 0.001-0.01); addition of H to FK506 resulted in an even greater fall in both the enzyme activities (P less than 0.001). Na-K ATPase activity increased in cell homogenates briefly incubated with cyclosporine in the ATPase reaction mixture (P less than 0.05) while FK506 reduced such enzyme activity (P less than 0.05), suggesting a direct effect of these agents on pump activity. These data in LLC-PK1 cells pocessing proximal tubular epithelial cell characteristics indicate that the combined use of cyclosporine plus FK506 may be very deleterious to viability in such cells. The opposing effects of cyclosporine and FK506 on PL-cyclosporine and Na-K ATPase activities and the possible potentiating effect of H on such responses are speculated to affect Na+ and water homeostasis in a manner that may explain differences in systemic blood pressure due to these agents.

Effect of triiodothyronine on system A amino acid transport in cells of rat submandibular gland.

The effect of L-3,5,3'-triiodothyronine (T3) on alpha-aminoisobutyric acid (AIB) transport in isolated cell suspensions of rat submandibular gland was investigated. The uptake of ATB by these cells appeared to require extracellular Na+ and was inhibited by ouabain (10(-3) M). Cell suspensions from thyroidectomized rats which have been given three successive doses of T3 on alternate days (50 micrograms/100 g BW) showed a significant increase in AIB uptake compared with cells isolated from thyroidectomized rats treated with diluent. Efflux of AIB from the cell suspension was not affected by T3. There was no significant changes in AIB uptake 12 h after a single injection of T3 (50 micrograms/100 g BW). However, there was a significant 49% and 65% increase in AIB net uptake at 24 and 48 h, respectively, after T3 treatment. Under similar conditions, the cell suspension showed a 48% increase in NaK-ATPase activity at 12 h and to a peak of 61% at 24 h. Therefore, changes in NaK-ATPase activity preceded the changes in AIB net uptake upon treatment with T3, implying that AIB uptake is probably mediated, at least in part, by the activity of NaK-ATPase.

Role of aldosterone for control of colonic NaKATPase activity in weanling rats.

Experiments were performed to examine how aldosterone modulates colonic NaKATPase activity during the weaning period. NaKATPase activity was determined in proximal and distal colon in control rats aged 16, 20, and 40 days, in rats aged 20 and 40 days fed low sodium diet for 4 days and in 20-day-old rats adrenalectomized on day 16. In some protocols net sodium and water transport was determined with in vivo perfusion technique. In control rats colonic NaKATPase activity increased significantly between day 16 and 20. This increase was abolished by adrenalectomy but restored by aldosterone substitution, 5 micrograms/100 g body weight/12 h. No significant increase in NaKATPase activity occurred between day 20 and 40. Serum levels of both aldosterone and of corticosterone were low until day 14 and increased to peak level at day 18-20. In 20- and 40-day-old rats fed a low sodium diet, NaKATPase activity increased significantly in proximal and distal colon in both age groups but the increases were significantly greater in the 20- than the 40-day-old animals. A low sodium diet increased serum aldosterone, but not serum corticosterone levels in both age groups: also the low sodium diet significantly increased net sodium and water transport in 20- but not in 40-day-old rats. Aldosterone is of physiological importance for the regulation of NaKATPase activity in the colon at the time of weaning. The immature colon may have an enhanced sensitivity to aldosterone.

622 DEVELOPMENT OF JEJUNAL NA-K ATPASE ACTIVITY

We studied effects of weaning on Na-K ATPase activity (which establishes the electrochemical gradient for active transport) in rat jejunal homogenates. Normal weaning (Day 21) led to an increase in enzyme activity after 24 hrs (4.26±.18 μmol Pi/mg/hr vs 2.31±.08 μmol Pi/mg/hr in suckling control littermates) (p<.05). Effect of Precocious Weaning (Day 16) (Activity μmol Pi/mg/hr) Effect of Artificially Delayed Weaning (Pups weaned on Day 25) These data indicate: 1) that weaning on Day 21 leads to an increase in Na-K ATPase activity in 24 hrs suggesting activation of preformed enzyme, 2) precocious weaning leads to a gradual increase in enzyme activity suggesting synthesis of new enzyme, and 3) no increase in activity occurs until weaning when weaning is artificially delayed suggesting that Na-K ATPase activity is not induced by endogenous free corticosterone which increases on Days 16-19 of age, which induces other intestinal enzymes.

Importance of adrenocortical hormones for maturation of colonic NaKATPase activity

NaKATPase activity is low in the immature rat colon and increases till the 40th postnatal day. Studies from this laboratory have shown that immature renal tubular cells are more sensitive to the inductive effect of adrenocortical hormones on NaKATPase activity than mature cells. The aim of this study has been to examine whether endogenous fluctuations of aldosterone (Aldo) and/or corticosterone (CS) induced by changes in sodium balance can precociously increase NaKATPase activity in the immature colon. Young and adult rats were therefore given a normal (C) or low sodium (E) diet for 4 days and studied at the age of 20 and 40 days, respectively.The effect of NaKATPase increase in 20 days secondary hyperaldo rats was evaluated using in vivo perfusion of colon. Net Na-absorption increased from control value 190 ± 91 μmol/min/dry g colon to 428.5 ± 97.2 (p < 0.05) and net fluid absorption increased from 1.02 ± 0.67 μl/min/dry g colon to 2.64 ± 0.75 (p < 0.05). These data indicate that aldosterone increases NaKATPase activity in proximal and distal colon, stimulates net sodium and water transport in large intestine and that the immature large intestine is more sensitive to aldosterone stimulation.

Peripheral effects of thyroid hormones: alteration of intracellular Na-concentration, ouabain-sensitive Na-transport, and Na-Li countertransport in human red blood cells.

To investigate the effect of thyroid hormones on erythrocyte cation transport systems and intracellular electrolyte content we have measured the activity of Na-K ATPase, Na-Li countertransport, as well as red cell sodium and potassium contents in patients with hyperthyroidism and in euthyroid controls. Intracellular Na- and K-concentrations were determined in erythrocytes washed three times in isotonic MgCl2 solution. Ouabain-sensitive Na-transport was estimated as the increase of Na before and after addition of ouabain in an erythrocyte suspension in isotonic Na-free medium. Na-Li countertransport was measured according to the method described by Canessa et al. [2]. The patients with hyperthyroidism exhibited a significantly elevated intracellular sodium content as well as a highly increased Na-K ATPase activity. Intracellular potassium content was not altered in the hyperthyroid subjects, but Na-Li countertransport was markedly decreased as compared to the controls. The results indicate that different ion transport systems of the erythrocyte membrane are influenced by thyroid hormones. We suggest that the elevation of Na-K ATPase activity might be due to the increased intracellular sodium concentration which is caused by the diminished countertransport pathway. Furthermore, the activity of Na-K ATPase, Na-Li countertransport, and intracellular sodium content in erythrocytes might be a useful peripheral indicator of thyroid hormone excess.

Effect of corticosterone and triiodothyronine on (Na+ + K+)-adenosine triphosphatase activity in rat submandibular gland.

The present study concerns the effect of glucocorticoids and triiodothyronine (T3) on rat salivary (Na+ + K+)-adenosine triphosphatase (NaK-ATPase). The results indicate that corticosterone increases submandibular gland NaK-ATPase activity with a single dose of hormone and with two daily doses on three successive days. Multiple injections of dexamethasone also increases submandibular and sublingual gland NaK-ATPase activity. The effect of glucocorticoids on salivary NaK-ATPase is selective since Mg-ATPase shows no significant differences under different steroidal states. We subsequently investigate the possibility of interaction between the effects of corticosterone and triiodothyronine on submandibular gland NaK-ATPase activity. Our studies indicate that each of these hormones increases NaK-ATPase activity in the absence of the other.