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Both epidemiologic and experimental evidence suggest that a high dietary sodium intake may increase airway responsiveness, but no adequate explanation exists of how changes in sodium intake might lead to increased responsiveness. This investigation was carried out to study dietary sodium intake and airway response to methacholine in relation to cellular sodium transport in 52 young men. Airway response to methacholine was associated with urinary sodium excretion when subjects were on normal sodium intake. Airway responsiveness in patients with mild asthma correlated with the furosemide-insensitive influx of sodium into peripheral leukocytes stimulated by autologous serum, but there was no relation between this influx and 24-h urinary sodium excretion. In a separate investigation, serum from subjects with increased airway responsiveness caused an increase in the sodium influx and sodium content of leukocytes from nonatopic subjects. The magnitude of the furosemide-insensitive, serum stimulated influx was related to the degree of airway responsiveness of the serum donor, as was the increase in intracellular sodium content. Neither was related to the 24-h urinary sodium excretion of the donor. Patients with airway hyperresponsiveness have an increased sodium influx into cells stimulated by a serum-borne factor. This is independent of the effect of added dietary sodium on airway responsiveness.

The relation between serum lipids, membrane fluidity, insulin, and the activity of the sodium-hydrogen exchanger was investigated in human lymphocytes from 83 subjects. Subjects had a wide range of serum lipids and no concurrent disease. Lymphocyte membrane anisotropy (inversely related to membrane fluidity) was measured with a fluorescence polarization method. Sodium-hydrogen exchange maximal proton efflux rate, affinity for external sodium, and resting pH were determined with the intracellular pH-sensitive fluorochrome 2',5'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Sodium-hydrogen exchange maximal proton efflux rate was negatively correlated with the age of the subject (p = 0.03). Membrane anisotropy correlated with serum triglyceride (p = 0.04). Multiple regression analysis demonstrated that the maximal proton efflux rate in human lymphocytes was significantly related to age (p = 0.005), systolic blood pressure (p = 0.04), membrane anisotropy (p = 0.03), and serum cholesterol (p = 0.03). Incubation of lymphocytes with insulin failed to affect sodium-hydrogen exchange kinetics, intracellular buffering power, or resting intracellular pH. These results suggest that membrane-bound transport proteins may be influenced by serum lipids and the fluidity of the lipid membrane in which they are bound, but they are unlikely to be affected by insulin.

It is hypothesized that endogenous inhibitors of active sodium transport may lead to an increase in peripheral vascular resistance. From studies in animal conduit arteries there is substantial evidence that cardiac glycosides may increase tension. A number of studies from our laboratory demonstrate that inhibition of active sodium transport may also increase tension in human resistance arteries, and that reduced Ca efflux via Na/Ca exchange could be a contributory mechanism. Further experiments also have suggested that endogenous inhibitors of sodium transport could lead to an increase in peripheral vascular resistance by reducing endothelium-dependent relaxation.

The in vitro effects of griffonin and ouabain on erythrocyte sodium content have been investigated in 6 normal subjects and 6 sickle cell patients. Intracellular sodium contents of normal or sickle cells incubated for 8 h in tris buffer, griffonin/tris buffer, or ouabain/tris buffer were determined. Incubation of normal cells in tris buffer or 0.5 mmol/l griffonin had little effect on the cell sodium content. However, 1.0 mmol/l griffonin/tris buffer raised the cell sodium level (P less than 0.05) over the incubation period. Ouabain/tris buffer (0.5 mmol/l or 1.0 mmol/l) also raised the sodium content (P less than 0.05 to P less than 0.001). Incubation of sickle cells in tris buffer raised the cell sodium (P less than 0.05) as did 0.5 mmol/l or 1.0 mmol/l griffonin (P less than 0.05 to P less than 0.001). Ouabain/tris buffer (0.5 mmol/l or 1.0 mmol/l) raised the intra-erythrocyte sodium level (P less than 0.01 to P less than 0.001). These findings suggest that ouabain and griffonin both have similar actions on intra-erythrocyte sodium content although ouabain was more potent. It is suggested therefore that griffonin could be a useful anti-sickling drug for sickle cell disease crisis.

1. Leucocyte Na+/H+ exchange and intracellular pH were investigated in physiological buffer containing bicarbonate. 2. The amiloride analogue 5-(N,N-hexamethylene) amiloride (1 x 10(-5) mol/l), an inhibitor of Na+/H+ exchange, had no significant effect on resting leucocyte pH, Na+ influx or Na+ content. 3. Ammonium chloride washout induced a profound intracellular acidosis, stimulating Na+/H+ exchange. This led to a 236% increase in Na+ influx. Eighty-eight per cent of this increase was inhibited by 5-(N,N-hexamethylene) amiloride. This demonstrates that 5-(N,N-hexamethylene) amiloride is an effective inhibitor of Na+/H+ exchange in human leucocytes. 4. The recovery from intracellular acidosis was shown to be dependent entirely on the presence of extracellular Na+. The Ki for inhibition by 5-(N,N-hexamethylene) amiloride of the recovery was 0.5 mumol/l. 5. Incubation with serum increased Na+ influx and Na+ content: the maximal effect was reached at 20% dilution. Serum (10%, v/v) increased influx by 40%, and 20% (v/v) serum by 102%, over resting levels. Only 43% of the serum-induced increase in Na+ influx was inhibited by 5-(N,N-hexamethylene) amiloride. This represented one-fifth of total Na+ influx. 6. Leucocyte intracellular pH increased on incubation with serum. This alkalinization was inhibited using 5-(N,N-hexamethylene) amiloride. 7. Studies of Na+/H+ exchange in leucocytes in physiological and pathological states are more likely to reflect the state in vivo if carried out in the presence of autologous serum.

Earlier work with rat arteries has resulted in a widely held assumption that resistance artery smooth muscle will not contract on exposure to a reduced transplasmalemmal sodium gradient. In view of the well-recognized low sensitivity of rat tissue to cardiac glycosides, we have investigated the effects of altering the transplasmalemmal sodium gradient on vascular smooth muscle tone by using human resistance arteries. Incubation of arteries in low sodium or in ouabain to inhibit active sodium efflux for 1 hour increased the contractile response to caffeine stimulation; this finding indicated enhanced calcium buffering by the sarcoplasmic reticulum. Prolonged incubation in ouabain in the presence of phentolamine or diltiazem resulted in a concentration-dependent increase in the tone of resting human resistance arteries. Reduction of the transplasmalemmal sodium gradient by incubation in low sodium buffer effected an increase in tone similar to that obtained in the presence of ouabain. These results suggest that alteration of the transplasmalemmal sodium gradient may increase the vascular smooth muscle tone of human resistance arteries by altering intracellular calcium handling. This is a new finding in human resistance arteries and may involve inhibition and, indeed, reversal of sodium-dependent calcium efflux. A concentration-dependent potentiation of tone was found after the addition of ouabain to submaximally activated arteries. Sodium-calcium exchange may also play a pivotal role in this mechanism.

In blacks and whites of similar socioeconomic background, the incidence of pregnancy-induced hypertension (PIH) is probably the same. In underdeveloped countries, however. PIH is often a life-threatening complication of pregnancy. Recent theories as to the etiology of PIH include the suggestion that vascular tone may be increased as a result of inhibition of active sodium transport in vascular smooth muscle. This may be the result of an inhibitor of sodium transport present in the serum. The literature concerning the demonstration of endogenous sodium transport inhibitors and endogenous digoxinlike immunoreactivity (EDLI) in PIH is reviewed and discussed.

1. The mechanism underlying the raised leucocyte sodium content in fulminant hepatic failure was studied by measurement of sodium fluxes, (Na+ + K+)-dependent adenosine triphosphatase activity, and leucocyte ATP content. 2. The rate constant for sodium efflux in the leucocytes was significantly reduced, and attributable to reduced activity of the enzyme (Na+ + K+)-ATPase. Leucocyte ATP content was not significantly different from that of control cells. 3. Incubation of cells from patients in the sera of normal subjects resulted in a reversal of these changes. Inhibition of the leucocyte sodium efflux rate constants and (Na+ +K+)-ATPase of normal cells was achieved by incubation in sera from patients. 4. We suggest that the raised sodium content of leucocytes in fulminant hepatic failure is attributable to a defective sodium pumping mechanism, possibly due to a circulating toxin.

Potassium chloride (96 mmol potassium/day) in the form of 12 Slow K tablets/day in 10 patients on an intake of 150 mmol sodium and 80 mmol potassium produced a cumulative sodium loss of 110 mmol by the 12th day of potassium supplementation. At the same time there was attenuation of the expected increase in plasma renin activity appropriate for such a sodium loss. The lack of rise in plasma renin activity and hence angiotensin II combined with sodium loss may account at least in part for the observed blood pressure fall. No change in ouabain-sensitive or total white cell sodium efflux rate constant was found. An effect of an increase in plasma potassium on the sodium pump cannot be excluded as the white cell sodium efflux rate constant was measured in a fixed external potassium concentration. There was no evidence from plasma noradrenaline measurements that increasing potassium intake reduces sympathetic activity in the resting state.

The intracellular sodium, potassium, and water content of isolated leucocytes was estimated in 47 patients with cirrhosis. The values for sodium showed a wide scatter. In patients without ascites the mean value was significantly increased but in those accumulating ascites it was normal, although often reduced in individual subjects. Reduced values were found in patients with hyponatraemia associated with end-stage cirrhosis and diuretic treatment. Changes in leucocyte water content closely followed those in sodium content. Leucocyte potassium content was normal except in patients accumulating ascites in whom it was significantly reduced, indicating whole body depletion, and this could be corrected by administration of spironolactone.

The active sodium transport of white cells and red cells obtained from patients with essential hypertension was impaired. Incubating white cells from normotensive subjects in serum obtained from patients with essential hypertension caused an impairment in sodium transport in the white cells of normotensive subjects similar to that found in the white cells of hypertensive patients. The impairment in sodium transport was due to a fall in the ouabain-sensitive component of the total sodium efflux rate constant. These results show that the serum of patients with essential hypertension contains a substance which influences sodium transport and that it has ouabain-like activity. They also suggest that it is this substance which causes the impairment in sodium transport in the leucocytes of patients with essential hypertension. These findings support the hypothesis that the rise in blood pressure in patients with essential hypertension is due to an increased concentration of a circulating sodium transport inhibitor which is continuously correcting a tendency for sodium retention by the kidney.

1. Leucocyte sodium transport was investigated as a possible assay for the small molecular weight natriuretic material isolated from the urine of normal subjects who had undergone volume expansion by saline infusion. 2. This fraction (fraction four or FIV), inhibitory to sodium transport in several other assays, was also found to inhibit leucocyte sodium transport. 3. FIV isolated from the urine of five normal subjects undergoing the natriuresis of mineralocorticoid 'escape' was also found to be inhibitory to leucocyte sodium transport. 4. Leucocytes isolated from the blood of the same subjects during mineralocorticoid escape showed decreased sodium transport.

1. In confirmation of previous studies, serum obtained from cord blood demonstrated endogenous digoxin-like immunoreactivity (EDLI). Sera from pregnant women in the third trimester also demonstrated EDLI, which disappeared after delivery. 2. Cord serum inhibited the total sodium efflux rate constant of a mixed leucocyte preparation when compared with the effect of control serum. This inhibition resulted from a depression of the ouabain-sensitive (sodium pump) component of the rate constant. 3. An ultrafiltrate of the serum (mol. wt. less than 30,000) also inhibited ouabain-sensitive leucocyte sodium transport when compared with filtrate obtained from control serum. 4. DHA-S Dehydroepiandrosterone sulphate (DHA-S) and cortisone, both present in high concentration in cord serum, demonstrated EDLI but did not affect leucocyte sodium transport in the cells of normal subjects. 5. DHA-S had no effect on sodium transport or vasoconstrictor activity in human omental resistance vessels. 6. It is concluded that EDLI of cord serum is associated with sodium transport inhibitory activity. This is unlikely to be attributable to DHA-S or cortisone.

Sodium transport in leucocytes of essential hypertensives was studied in physiological media. Untreated hypertensives have depressed values for the total and ouabain-sensitive sodium efflux rate constant. Treatment with diuretics abolished this abnormality. These results are compatible with the presence of a circulating inhibitor of sodium transport in essential hypertension.

Leucocyte sodium efflux was measured in control leucocytes pre-incubated for 90 min with serum from patients with advanced liver cirrhosis. Serum from patients with advanced alcoholic liver cirrhosis was inhibitory to sodium transport in control leucocytes. The degree of inhibition was similar to that seen in the patients' own leucocytes; the defect induced by patient serum was primarily inhibition of ouabain-insensitive sodium efflux, whereas in the patients' own leucocytes, inhibition was seen in both ouabain-sensitive and -insensitive sodium efflux, as shown previously. The results suggest that a circulating factor, present in patients with advanced cirrhosis, is capable of inhibiting sodium transport in leucocytes.

Previous studies have demonstrated abnormalities of intracellular electrolyte content and sodium transport in leukocytes of patients with fulminant hepatic failure. The current study was undertaken to establish whether similar abnormalities were present in patients with encephalopathy from advanced cirrhosis. Results from 19 patients with advanced cirrhosis showed values for the leukocyte total sodium efflux-rate constant were significantly reduced in patients, 3.02 +/- 1 SEM 0.12 h-1, compared to control values, 3.80 +/- 0.06 h-1. This reduction was due primarily to a lowering of the ouabain-sensitive component of sodium efflux, a measure of Na,K-ATPase activity. In comparison, leukocytes from patients with fulminant hepatic failure show a greater inhibition of the ouabain-sensitive component of sodium efflux with a raised ouabain-insensitive efflux. Although cirrhosis has generally been associated with potassium depletion, the intracellular potassium content of the cirrhotic patients' leukocytes was normal. Since the leukocyte is considered to be a good cell model and because abnormalities of sodium transport have been shown in the leukocytes of these patients, it is likely that similar abnormalities of sodium transport are present in other organs, including the brain.

1. Serum from patients with fulminant hepatic failure inhibits the ouabain-sensitive sodium efflux in leucocytes. A 1 : 100 dilution of the serum was necessary before the inhibition became undetectable. 2. Dialysates of the serum through cuprophane in vitro and polyacrylonitrile haemodialysis in vivo were inhibitory in small amounts. 3. Ultrafiltrates ( less than 10 000 daltons) of serum were chromatographed on Sephadex G-25 and the elution profile obtained from patients with fulminant hepatic failure was both qualitatively and quantitatively different from that of normal controls. Material from peaks 3, 4, 5 and 7 in patients with fulminant hepatic failure inhibited leucocyte sodium transport. 4. dialysate from haemodialysis with the polyacrylonitrile membrane contained most peaks, particularly peaks 4 and 5. Adsorption of serum with polymer coated charcoal in vitro largely removed peaks 5-8.

The sodium content of peripheral blood leucocytes was estimated in two separate investigations of the relationship between cellular sodium content and the vasoconstrictor state. In the first study various parameters of forearm blood flow were measured in a group of 31 normal subjects. A positive correlation was found between peripheral vascular resistance and leucocyte sodium content (p less than 0.05), and a negative correlation between venous compliance (VV60) and leucocyte sodium content (p less than 0.001). In the second study the leucocyte sodium content of 14 patients with essential hypertension was investigated before and after treatment with the calcium antagonist verapamil. The sodium content was found to be abnormally high, as previously described, and treatment with verapamil was found to reverse the defect. Both studies indicate a link between cell sodium content and the vasoconstrictor state, and the results are discussed in light of current theory.

Sodium transport has been studied in thymocytes of one-kidney, one-clip (1K, 1C) and two-kidney, one-clip (2K, 1C) models of hypertension in the rat. No differences of intracellular sodium or sodium transport could be demonstrated in either model when compared with sham-operated controls. The experiments provide no evidence to support the concept that an inhibitor of sodium transport is associated with the development of hypertension in the one-kidney, one-clip rat. A previously unrecognized effect of incubation time and cell density on thymocyte sodium metabolism is reported.

Intracellular sodium content and ouabain-sensitive sodium efflux rate constant were measured in leucocytes and erythrocytes from subjects with untreated essential hypertension and also in normotensive subjects with and without a family history of hypertension. Leucocytes from hypertensives were again shown to have a higher intracellular sodium content and lower ouabain-sensitive sodium efflux rate constant than normotensive controls but there were no differences between those normotensive subjects with and those without a family history of hypertension. No differences in erythrocyte sodium content or efflux rate constant were seen between any of the three groups.

Dietary sodium restriction (10 mmol Na/day) for a period of 2 weeks did not result in any change in the blood pressure of 12 healthy young adults (mean age 21). There was also no change in their leucocyte sodium transport investigated immediately before the diet and on the last day. Sodium restriction (10 mmol Na/day) in 12 middle-aged hypertensive subjects (mean age 56) for the same period of time caused a significant fall in both systolic and diastolic blood pressure. The leucocyte total sodium efflux rate constant was initially low, but after the diet significantly increased towards the control value. The results are compatible with the theory that a circulating sodium transport inhibitor is present in patients with essential hypertension, and is related to salt intake.

1. Endogenous digoxin-like immunoreactivity (EDLI) was measured by radioimmunoassay for digoxin in 13 paired samples of arterial and venous umbilical cord serum. EDLI was present in vein and artery, but was higher in the venous samples (P less than 0.025). 2. The venous cord serum inhibited the ouabain-sensitive sodium efflux rate constant of a normal mixed leucocyte population when compared with the effect of arterial cord serum (P less than 0.005). 3. It is suggested that the placenta may be involved in the production or metabolism of neonatal EDLI and of the inhibitor of sodium transport.

The effect of treatment with verapamil on cell sodium transport was studied in the leucocytes of patients with essential hypertension. Previously described abnormalities of sodium efflux rate constant and intracellular sodium content were confirmed, the component of the sodium efflux rate constant sensitive to ouabain being lower and the intracellular sodium content higher in the patients compared with controls. Verapamil reversed these abnormalities and reduced blood pressure.

Sodium efflux rate constants and intracellular sodium were measured in leucocytes from healthy volunteers in the presence and absence of the calcium antagonist verapamil hydrochloride. Verapamil stimulated sodium pump activity and this effect was dependent on the presence of external calcium. Verapamil has been reported to reverse the abnormality of sodium transport seen in leucocytes from patients with essential hypertension and the present study demonstrates that sodium pump activity in leucocytes from control subjects is also stimulated by exposure to verapamil in vitro. This direct cellular effect appears to be due to the calcium antagonist properties of the drug.