We have used87Rb nuclear magnetic resonance spectroscopy (NMR) to study in vivo rubidium kinetics in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) controls, using rubidium as a marker for potassium. We gave 15 male, 13-week-old SHR, mean \u00b1 s.d. blood pressure 180 \u00b1 10mmHg, and 15 age-matched normotensive controls, mean blood pressure 120\u00b19mmHg, a daily dose of RbCl (2 mmol/kg intraperitoneally). We made repeated NMR measurements of skeletal muscle rubidium concentrations until steady state was reached. We then withdrew rubidium and made further measurements of rubidium concentrations, at intervals, for up to 1 week after the last injection. We also measured plasma and erythrocyte rubidium concentrations by flame atomic absorption spectroscopy at similar intervals after the withdrawal of rubidium. Rubidium concentrations rose at a faster rate in SHR skeletal muscle, but the steady-state muscle rubidium concentration was the same (45 mmol/l) in both SHR and WKY rats. There was also a threefold increase in the rate of rubidium efflux from both muscle and erythrocytes in SHR. These results are consistent with a marked increase in Na+, K+ -ATPase activity and an increase in the rate of rubidium efflux in vivo in SHR. The increased rate of rubidium efflux in SHR could represent increased K+ efflux via calcium-activated K+ channels and/or result as part of cell volume regulation secondary to increased Na+ -H+ antiporter activity. \u00a9 Current Science Ltd.
\n \n\n \n \nWe have assessed the in vivo activity of the Na +-H+ antiporter skeletal muscle in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) controls using phosphorus (31P) nuclear magnetic resonance spectroscopy to measure changes in cytosolic acid concentrations during isometric contraction. During contraction there was a smaller rate of rise in skeletal muscle cytosolic acid concentration to a smaller maximum concentration in SHR. This difference in acid response was removed by amiloride and was not attributable to differences in cell buffering or the rate of production of lactic acid, suggesting that the difference in acid response in SHR skeletal muscle is due to increased in vivo Na + -H+ antiporter activity. Amiloride reduced resting muscle glycogen concentration and increased muscle lactate concentration in the SHR. This could be related to altered in vivo calcium metabolism. The maximum tension produced by skeletal muscle during contraction in SHR was less than in WKY rats, and relaxation between twitches was significantly greater, consistent with the finding of increased vascular smooth muscle relaxation in essential hypertension. Since increased Na + -H+ antiporter activity occurs in association with increased relaxation of both skeletal and vascular smooth muscle, these data are not consistent with a relationship between increased Na+-H+ antiporter activity and increased maximal muscle tension development. However, they show that increased Na + -H+ antiporter activity is associated with increased muscle relaxation. \u00a9 Current Science Ltd.
\n \n\n \n \nA randomised, double blind, placebo controlled, crossover study of digoxin withdrawal and reintroduction was carried out over two periods of eight weeks each after long term treatment. Forty four patients with stable heart failure in sinus rhythm and plasma digoxin concentrations over 0.8 ng/ml were studied. Their progress was assessed by clinical criteria, by haemodynamic measurements (systolic time intervals and echocardiography), and by pharmacological measurements of erythrocytic sodium pump numbers and activity. After withdrawal of digoxin clinical deterioration occurred in only 25% ofthe patients. Furthermore, in only 9% of cases was digoxin reintroduction thought to be necessary. There was deterioration in only 11% of the patients during digoxin treatment. Deterioration during digoxin withdrawal was accompanied by changes in systolic time intervals, but similar, albeit smaller changes in systolic time intervals also occurred in patients with no deterioration. Deterioration was accompanied by changes in the pharmacological effects of digoxin on the erythrocytes, consistent with a loss of effect, and these changes did not occur in those who did not deteriorate. The-occurrence of deterioration could not be predicted by any clinical, haemodynamic, or pharmacological measurements made before withdrawal.
\n \n\n \n \nWe have used a novel technique to assess the transport of cations across the erythrocyte membrane in vivo in unmedicated patients suffering an acute manic illness. The results show that erythrocyte cation transport via the sodium-pump enzyme Na+,K+-ATPase is increased in manic patients compared with healthy controls.
\n \n\n \n \nWe have measured cation transport in vivo in seven healthy volunteers under control conditions and after they had taken lithium carbonate for 21 days in doses which maintained the serum lithium concentration in the range 0.6-0.8 mmol/l. We have measured cation transport in vivo after the administration of an oral load of rubidium chloride, and have found that, although intra-erythrocytic concentrations of rubidium were significantly lower 1 h after the administration of rubidium when the subjects were taking lithium, there was a significant increase in the rate of uptake of rubidium into the erythrocytes over the subsequent period of the test, suggesting a direct stimulation of sodium, potassium-activated adenosine triphosphatase by lithium. Lithium administration did not affect the plasma concentration versus time profile of rubidium after the rubidium load, implying that the lithium-stimulated uptake of rubidium which occurs in erythrocytes does not necessarily occur in other cell types. These results suggest that previous studies of cation transport using peripheral cells and assay systems in vitro do not necessarily reflect changes in cation transport in vivo in excitable tissues.
\n \n\n \n \nWe have investigated cation transport in vivo in patients being treated with lithium for bipolar affective illness by studying the disposition of rubidium after an oral load of rubidium chloride. The rate of erythrocyte cation transport was increased in the patients when compared with matched healthy volunteers. However, the rate of in-vivo erythrocyte rubidium accumulation in the euthymic treated patients was significantly lower than in a matched group of unmedicated manic patients. The regulation of specific pathways for cation transport may be altered in individuals predisposed to affective illness.
\n \n\n \n \n1. We have given an oral load of lithium carbonate to healthy volunteers in order to investigate the transport of lithium across the erythrocyte membrane in vivo and the effects of known inhibitors of that transport. 2. Using this technique we have shown that pretreatment with either digoxin, an inhibitor of the sodium/potassium pump, or dipyridamole, an inhibitor of the anion transporter, does not alter the plasma or erythrocyte lithium concentration profiles, nor any of the pharmacokinetic variables derived from these data, and we conclude that these two transport pathways do not contribute significantly to the in vivo handling of lithium by erythrocytes. 3. We have also shown that erythrocyte lithium concentrations measured directly differ significantly from the predicted concentrations calculated using the two\u2010compartment pharmacokinetic model which has been used in some earlier comparisons of in vitro and in vivo lithium handling. 4. We suggest that the in vivo administration of lithium carbonate may permit a specific measure of the in vivo activity of the sodium/sodium countertransport pathway. 1989 The British Pharmacological Society
\n \n\n \n \nWe have quantified specific [3H]\u2010ouabain binding sites in normal human lymphocytes, and have measured the changes in the numbers of those sites which occur in response to various stimuli. We have confirmed previous findings that incubation for 72 h in the presence of fetal calf serum causes an increase in [3H]\u2010ouabain binding, and that this does not occur if the cells are incubated in fetal calf serum which has first been dialysed. During incubation of the lymphocytes for 3 days in the presence of dialysed fetal calf serum each of the following stimuli caused an increase in specific [3H]\u2010ouabain binding: addition of ethacrynic acid (1 mumol l\u20101), addition of lithium (1 mmol l\u20101), and reduction of the external potassium concentration (to 0.75 mmol l\u20101). By analogy with the similar results in HeLa cells reported by others, we suggest that the increase in [3H]\u2010ouabain binding may, in the case of ethacrynic acid and the reduction of the external potassium concentration, be initiated by an increase in the intracellular sodium concentration. The mechanisms whereby fetal calf serum and lithium cause an increase in [3H]\u2010ouabain binding are not clear. 1986 The British Pharmacological Society
\n \n\n \n \n1. In order to study cation transport in vivo we have measured the changes in plasma and intra-erythrocytic rubidium concentrations after the oral administration of rubidium chloride. 2. In this paper we describe our findings in 22 patients with untreated essential hypertension, compared with the findings in 22 carefully matched control subjects. Our findings in patients receiving short-term digoxin therapy and in patients with chronic renal failure are also included for comparison. 3. Whereas the findings in patients receiving digoxin and in patients with chronic renal failure are compatible with a widespread reduction in sodium,potassium-ATPase activity in vivo, the findings in patients with untreated essential hypertension are not. 4. Further analysis of the data and a similar study of the disposition of 42K after the intravenous administration of 42KCl suggest that in vivo net cation transport is enhanced in the erythrocytes of patients with untreated essential hypertension.
\n \n\n \n \nWe have studied the effects of digoxin on cation transport in vivo by measuring the changes in plasma and red cell rubidium concentrations following an oral load of rubidium chloride. In eight patients who had been taking digoxin for 7 to 10 days (mean plasma digoxin concentration 1.3 ng ml\u20101) the rise in plasma rubidium concentrations was enhanced and the rise in red cell rubidium concentrations was attenuated following the oral load of rubidium chloride, by comparison with the changes in well\u2010matched controls. In contrast, the disposition of rubidium was not altered in 12 patients who had been taking digoxin for more than 3 months (mean plasma digoxin concentration 1.1 ng ml\u20101). These results suggest that the inhibitory effects of digoxin on cation transport are detectable in vivo during short\u2010term therapy, but not during long\u2010term therapy, and confirm our previous in vitro findings. 1986 The British Pharmacological Society
\n \n\n \n \nThe pharmacokinetics of L\u2010tryptophan (5 g and 7.5 g) have been studied after its intravenous administration to healthy subjects and the results compared with those obtained after oral administration (0.7 g\u2010 3.5 g). In order to do this, we have re\u2010analysed previously published data relating to oral administration. The data obtained following the oral administration of L\u2010tryptophan suggest that the total body clearance and apparent volume of distribution are saturable. The pharmacokinetics of tryptophan after intravenous administration of 5 g and 7.5 g were similar to those after the oral administration of 25 and 50 mg kg\u20101 (i.e. 1.75 g and 3.5 g). Similar pharmacokinetic values were obtained following intravenous tryptophan when the same subjects were retested after a period of 2\u20104 weeks. 1985 The British Pharmacological Society
\n \n\n \n \nWe have measured intracellular sodium concentrations and specific 3H-labelled glycoside binding characteristics in the erythrocytes and leucocytes of patients with untreated essential hypertension, and have compared the results with those in well-matched normotensive control subjects. Intracellular sodium concentrations were increased in the leucocytes, but not in the erythrocytes, of patients with untreated essential hypertension. There were no differences in the 3H-labelled glycoside binding characteristics of either the erythrocytes or the leucocytes of hypertensive and normotensive subjects. There was no difference in the ability of plasma samples from hypertensive and normotensive subjects to inhibit the binding of [3H]-ouabain to intact leucocytes from normotensive subjects. These findings are not consistent with the presence of increased concentrations of a substance which behaves like a cardiac glycoside in the circulation of patients with untreated essential hypertension.
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