Adrenergic modulation of extrarenal potassium disposal

Inter-relationship between serum potassium and plasma catecholamines and 3':5' cyclic monophosphate in alcohol withdrawal

Serial analyses of serum potassium and plasma epinephrine, norepinephrine and adenosine 3':5'-cyclic monophosphate (cyclic AMP) concentrations were measured in 13 patients with alcohol withdrawal, six of whom presented delirium tremens. Patients with delirium showed at admission levels of potassium (3.45 +/- 0.45 mmol/l) lower (P less than 0.02) than patients without delirium (3.81 +/- 0.14 mmol/l). Three patients were hypokalemic, all of them with delirium. Serum potassium increased significantly in all the patients during evolution. A close negative correlation (r = -0.751) between the intensity of withdrawal and serum potassium was observed. Plasma epinephrine concentrations were increased at admission (623 +/- 192 pmol/l), patients with delirium showing greater values (705 +/- 137 pmol/l). As the alcohol withdrawal improved, plasma epinephrine concentration decreased. Plasma norepinephrine concentrations were also increased at admission (3422 +/- 1451 pmol/l), but did not change significantly during evolution, being similar in patients with and without delirium. Plasma cyclic AMP levels were high at admission (40.4 +/- 24.3 nmol/l) and increased significantly (P less than 0.05) during evolution. The data obtained suggest that in patients with alcohol withdrawal, as symptomatology improves, plasma epinephrine decreases, while plasma norepinephrine remains increased. The combined actions of the two facts--less beta-stimulus, maintaining of alpha-stimulus--would comprise a significant increase of kalemia, that in cases of initial hypokalemia would lead to normal values of serum potassium.

Acute increase in plasma osmolality as a cause of hyperkalemia in patients with renal failure

These studies were performed in patients with chronic renal failure to understand the mechanism(s) of hyperkalemia secondary to hypertonic NaCl infusion. In 10 patients, after intravenous infusion of either 5% or 2.5% NaCl (6 mEq per kg body wt for 120 minutes in both solutions), the maximum increase in plasma potassium averaged 0.6 (range 0.3 to 1.3) mmol/liter (P less than 0.01) or 0.3 (range 0.2 to 0.6) mmol/liter (P less than 0.01), respectively. The rise of both plasma potassium and osmolality was significantly higher during 5% NaCl than during 2.5% NaCl infusion (P less than 0.01). A significant linear correlation (P less than 0.01) between plasma potassium and osmolality was observed. Urinary potassium excretion was increased to a similar extent by 5% NaCl and 2.5% NaCl infusion. The observed hyperkalemia, secondary to NaCl infusion, was independent of venous pH, plasma bicarbonate, anion gap, insulin levels, and urinary norepinephrine and epinephrine excretion, and was associated with a fall in plasma aldosterone concentration. In separate studies, nine patients were treated with desoxycorticosterone acetate (DOCA; 20 mg i.m. for three days) before receiving saline (5%) infusion. DOCA did not prevent the level increase in plasma potassium that remained significantly correlated with plasma osmolality (P less than 0.01). In conclusion, hypertonic NaCl infusion in patients with renal failure causes a clinically relevant hyperkalemia despite increased renal excretion of potassium. This hyperkalemia is independent of acid-base or hormonal mechanisms known to regulate extrarenal homeostasis of potassium, and is strictly correlated with a rise in plasma osmolality.

Pre-operative anxiety and serum potassium

Small decreases in serum potassium in a study of 200 pre-operative patients were demonstrated in those who had an increase in anxiety, as measured on a linear analogue anxiety scale, in the 24 hours before anaesthesia. The possible aetiology and implications of this change are discussed. The combination of temazepam and a pre-operative visit by the anaesthetist effectively reduced pre-anaesthetic anxiety in 60% of patients.

Disorders of potassium homeostasis

Derangements in potassium homeostasis affect the body's bioelectric processes, including muscle contraction, nerve conduction, and myocardial electric pacing. Changes in extracellular potassium concentration occur with altered routes of elimination (renal or gastrointestinal) or with pathologic shifts in potassium from one body fluid compartment to another. The therapeutic interventions may either restore a normal resting potential for excitable cells or affect the threshold potential. Thus, an understanding of the basic pathophysiology is the foundation for treatment.

A patient with hyperkalemia and metabolic acidosis

Uptake of potassium by extrarenal tissues, primarily muscle and liver, represents a major defense mechanism in the maintenance of normokalemia following an acute elevation in the serum potassium concentration. Insulin, epinephrine, and aldosterone all play major roles in maintaining the normal distribution of potassium between the intracellular and extracellular environment. In addition to hormonal regulation, changes in blood pH and tonicity also exert a strong influence on extrarenal potassium metabolism. Last, the serum potassium concentration per se directly influences its own cellular uptake and this transport mechanism appears to be inhibited by uremia.

Interaction of the sympathetic nervous system and electrolytes in congestive heart failure

Congestive heart failure is characterized by both disturbances in electrolyte homeostasis and neuro-hormonal regulation. Total body potassium is reduced, and this reduction bears a modest relation to activation of the sympathetic nervous system and the renin-angiotensin-aldosterone system. Patients with decompensated heart failure show increases in both plasma epinephrine and plasma norepinephrine, whereas patients with chronic stable heart failure usually have an increase only in plasma norepinephrine. High levels of circulating epinephrine may contribute to the development of hypokalemia by activating skeletal muscle and liver membrane beta 2-adrenergic receptors, which in turn stimulate intracellular cyclic adenosine monophosphate to activate the membrane-bound Na+K(+)-adenosine triphosphatase pump. The net result is that potassium flux across the cell membrane from the extracellular to the intracellular space increases, setting the stage for hypokalemia and possibly serious ventricular arrhythmias. Other mechanisms that may contribute to the development of hypokalemia in heart failure include the kaliuresis brought on by excessive levels of aldosterone. Moreover, it is likely that the activity of facilitated by concomitant activation of the renin-angiotensin system. Increased sympathetic nerve activity may then release additional renin from the kidney (by way of a beta 2-adrenergic mechanism). Therefore, both the sympathetic nervous system and the adrenal medulla may interact to cause hypokalemia in patients with heart failure. Because hypokalemia is known to predispose patients to ventricular arrhythmias, it may be prudent to aggressively maintain serum potassium levels in patients with heart failure in the range of 4 to 5 mEq/liter.

Influences of thyroid status and sympathoadrenal system on extrarenal potassium disposal

Effects of hyper- and hypothyroidism on the ability of rats to transfer acute intravenous loads of potassium from the extracellular to the intracellular milieu (extrarenal potassium disposal, ERPD) were studied. We also examined the effects of the sympathoadrenal system on ERPD, as well as the manner in which it interacts with thyroid status. Experiments were performed in thyroidectomized (hypothyroid), sham-operated (euthyroid), or 3,5,3'-triiodo-L-thyronine-treated (thyrotoxic) rats. In anesthetized, acutely nephrectomized animals given a constant infusion of KCl over a 90-min period, ERPD was assessed as an inverse function of the increase in plasma potassium concentration. Some animals were subjected to chemical sympathectomy, adrenalectomy, the administration of adrenergic antagonists, or the infusion of adrenergic agonists. The effects of these treatments in various combinations on ERPD in animals of differing thyroid status were determined and the following conclusions could be drawn: 1) beta 2-adrenergic influences increase ERPD; 2) alpha 1- and alpha 2-adrenergic influences decrease ERPD; 3) these influences of the sympathoadrenal system on ERPD are qualitatively independent of thyroid status, and in all three thyroid states, beta-adrenergic enhancement predominates over alpha-adrenergic inhibition; 4) thyrotoxicosis increases and hypothyroidism decreases ERPD, and these effects are qualitatively independent of the presence of sympathoadrenal activity; 5) the intrinsic effect of thyroid hormone insufficiency and increased alpha-adrenergic tone and/or responsiveness together account for the decreased ERPD observed in hypothyroid animals; and 6) the intrinsic effect of thyroid hormone excess and increased beta-adrenergic tone and/or responsiveness, as well as decreased alpha-adrenergic tone and/or responsiveness, together account for the increased ERPD found in thyrotoxic animals.

Emergencies in continuous dialysis patients: diagnosis and management

The number of patients undergoing long-term hemodialysis and peritoneal dialysis is growing in the United States. To provide adequate emergent care to these patients emergency physicians must understand the alterations in normal physiologies present in these patients and how this may affect care. Cardiovascular disease and infection (especially Staphylococcus aureus sepsis) are the leading causes of death among dialysis patients. These patients are also subject to a significantly higher incidence of life-threatening electrolyte disturbances, particularly hyperkalemia and hypercalcemia, than the general population. Suicide, cardiac tamponade, intracranial hemorrhage, bleeding disorders, and bowel infarction are also much more frequent. The inability of dialysis patients to excrete drugs, metabolites, toxins, and fluids significantly alters their responses to common emergencies and should directly influence their care. Failure to recognize these differences in physiology may result in the use of standard forms of emergency therapy that may compound, rather than treat, the underlying disorder. Although most dialysis patients who come into an emergency department have conditions that can, and should, be managed by their nephrologist, the presence of a life threatening emergency requires prompt, appropriate therapy by the emergency physician.

Adrenergic modulation of potassium metabolism in uremia

The effect of chronic beta adrenergic blockade on potassium homeostasis during moderate intensity exercise (40% of VO2 max) was examined in seven end-stage renal patients who were being maintained on chronic dialysis treatment. Subjects participated in three study protocols: 1) exercise alone, 2) exercise plus propranolol (a nonselective beta-1, beta-2 antagonist), and 3) exercise plus metoprolol (a specific beta-1 antagonist). The basal potassium concentration was similar in all three studies and averaged 4.95 +/- 0.12 mEq/liter. During Study 1 (exercise alone), plasma potassium rose by 0.26 +/- 0.09 mEq/liter. During exercise with propranolol, plasma K concentration rose significantly higher (delta plasma K = 0.44 +/- 0.26 mEq/liter; P less than 0.05 vs. exercise alone). In contrast, the rise in plasma K during exercise with metoprolol (delta plasma K = 0.20 +/- 0.08 mEq/liter) was similar to that observed with exercise alone. Differences in potassium homeostasis between metoprolol and propranolol could not be explained by differences in hemodynamic parameters, levels of potassium regulatory hormones, or acid base status. Thus, the higher rise in potassium concentration during exercise with propranolol could only be explained by adrenergic blockade at the beta-2 receptor site. These results support the concept that adrenergic control of extrarenal potassium homeostasis in dialysis patients is mediated at the beta-2 receptor. Since a deterioration in potassium homeostasis during exercise is observed with beta-2, but not beta-1 blockade, selective beta-1 adrenergic blocking agents may be safer in dialysis patients.

Potassium homeostasis during angiotensin-converting enzyme inhibition with enalapril

The effect of angiotensin-converting enzyme (ACE) inhibition on renal and extrarenal potassium (K) regulation was examined. Six healthy men were studied in double-blinded crossover fashion on placebo or enalapril, 80 mg/day. On day 4, the subjects were given an intravenous infusion of KCl and on day 5 an oral dose of 10% NH4Cl. Treatment with enalapril decreased plasma aldosterone and increased plasma renin activity (PRA), epinephrine and norepinephrine, but did not affect serum glucose, plasma insulin or basal plasma K. Maximal increases in plasma K during K infusion or NH4Cl ingestion were similar during enalapril and placebo treatment. With enalapril treatment urinary K excretion was unchanged following K loading but moderately reduced following NH4Cl loading. We conclude that ACE inhibition does not acutely impair K homeostasis in men with normal renal function.

Therapy of acute bronchospasm. Complicated by lactic acidosis and hypokalemia

Hypokalemia and lactic acidosis developed following correction of respiratory acidosis in a 5-year-old child who presented with respiratory failure secondary to severe asthma and treated with theophylline, inhaled albuterol, and parenteral methylprednisolone. Calculation of the "anion gap" that provided the clue to presence of lactic acidosis was confirmed by the measurement of serum lactate level.

Feline kaliopenic polymyopathy/nephropathy syndrome

The prevalence of hypokalemia in cats has probably been underestimated until recently. Like many other "contemporary" diseases, this syndrome is probably not new; however, it is now more easily recognized because of the identification of associated dietary and disease risk factors, clinical signs, and laboratory abnormalities, which have been linked to the expected pathophysiology of potassium depletion in the cat.

Exercise-related changes in serum catecholamines and potassium: effect of sustained exercise above and below lactate threshold

Plasma potassium and catecholamines exhibit rapid shifts during exercise testing, particularly when exercise intensity exceeds lactate threshold. To assess changes that may occur during sustained exercise, we studied 10 healthy men to determine the effect of 20 minutes of exercise at 25 W above lactate threshold (ALT) and 20 minutes of exercise at 25 W below lactate threshold (BLT). Both conditions showed elevation of catecholamines at end exercise compared to baseline, but catecholamine levels ALT were significantly higher than the levels BLT (2270 +/- 190 versus 900 +/- 230 pg/ml norepinephrine, p less than 0.001; 509 +/- 69 versus 150 +/- 18 pg/ml epinephrine, p less than 0.001). This difference persisted at 2 minutes of recovery (1620 +/- 130 versus 590 +/- 60 pg/ml norepinephrine, p less than 0.001; 216 +/- 31 versus 98 +/- 16 pg/ml epinephrine, p less than 0.001). Both conditions resulted in a significant elevation in potassium at end exercise compared to baseline, but the potassium levels ALT were significantly higher than the levels BLT (1.1 +/- 0.1 mEq/L versus 0.5 +/- 0.1 mEq/L, p less than 0.001. The fall in potassium in the immediate post-exercise period was significantly greater following exercise ALT (-0.8 +/- 0.1 mEq/L versus -0.2 +/- 0.1 mEq/L, p less than 0.001). Thus sustained exercise slightly ALT resulted in a significant potassium flux and very elevated catecholamine levels. Avoiding these metabolic stresses by exercising BLT may decrease chances for exercise-related arrhythmia or other cardiac dysfunction in susceptible patients.

Effect of dobutamine on plasma potassium in congestive heart failure secondary to idiopathic or ischemic cardiomyopathy

Dobutamine was administered in a dose of 10 +/- 1 micrograms/kg/min to 13 patients with severe idiopathic or ischemic dilated cardiomyopathy. Acute hemodynamic improvement was noted in all patients. All patients had a significant decrease in plasma potassium (4.6 +/- 0.1 to 4.2 +/- 0.2 mEq/liter, p less than 0.0001) at peak infusion. The decrease in potassium persisted for at least 45 minutes after discontinuing the infusion. Three patients had exacerbation of baseline ventricular arrhythmias that resolved with infusion discontinuation. Changes in plasma norepinephrine could not explain the potassium decrease or arrhythmia production, which also significantly decreased in these patients (771 +/- 123 to 524 +/- 73 pg/ml, p less than 0.01). It is concluded that dobutamine causes a significant decrease in plasma potassium and that the decrease persists at least 45 minutes after the infusion is discontinued.

Skeletal muscle beta 2-adrenoreceptors and the effect of adrenergic drugs on plasma potassium in perinephritis hypertension in rabbits

1. It has been suggested that beta 2-adrenoreceptors in skeletal muscle regulate plasma potassium. The possibility that alterations in the function and/or density of these receptors occurs in perinephritis hypertension in rabbits was studied. 2. Intravenous infusion of adrenaline (0.2 micrograms kg-1 min-1) caused a fall in potassium while intravenous bolus injection of propranolol (0.75 mg kg-1) resulted in an increase in serum potassium which was of similar magnitude in both perinephritis hypertensive and sham-operated normotensive rabbits. 3. Binding studies with the radioligand [125I] cyanopindolol (ICYP) showed that there were no significant differences between the hypertensive and normotensive rabbits in the density (Bmax) or affinity (KD) of the skeletal muscle beta 2-adrenoreceptor. 4. The results suggest that function and density of skeletal muscle beta 2-adrenoreceptors are not altered in rabbits with perinephritis hypertension.

Hypokalaemia in severe head trauma

Forty-six consecutive patients with severe isolated head trauma (GCS less than or equal to 7) had significant hypokalaemia averaging 3.1 +/- 0.4 (S.D.) mmol/litre upon admission to the emergency room. This electrolyte imbalance occurred within hours of the trauma and resolved under treatment within the first day. There was no correlation between serum potassium and pH, glucose, urine electrolytes, patient age or sex, admission Glasgow Coma Score or the Glasgow Outcome Score. Sixteen patients with multiple trauma but without head trauma had an average serum potassium of 3.5 +/- 1.1 mmolar. Mechanisms of serum potassium level control and their correlation with brain trauma are addressed in a search for an explanation of this phenomenon. We believe that the most appropriate explanation for this hypokalaemia is the large catecholamine discharge that is known to accompany severe head trauma, with resultant beta 2-adrenergic stimulation of the Na+ -K+ pump. The formation of a prospective on-going study to clarify the basic mechanism of hypokalaemia in severe head trauma is presented.

Fosenopril, an angiotensin-converting enzyme inhibitor, and propranolol: comparative effects at rest and exercise on blood pressure, hormonal variables, and plasma potassium in essential hypertension

Fosenopril sodium, a prodrug, is converted to its active diacid during and after intestinal absorption. Its excretion is equally divided between hepatic and renal routes. This placebo-controlled, randomized, double-blind, parallel group study evaluated the efficacy and safety of fosenopril compared to propranolol, at rest and during exercise, on blood pressure, plasma potassium, plasma renin activity, and plasma aldosterone. Exercise testing utilized bicycle ergometry, and individual subjects underwent an identical exercise protocol on placebo and on active treatment. The fosenopril group comprised nine subjects who were matched to nine subjects on propranolol. Blood pressure fell significantly and equally at rest (fosenopril--157/103 to 141/95 mmHg, p less than 0.005; propranolol--159/100 to 149/90 mmHg p less than 0.005) and during exercise in both groups. Plasma potassium fell significantly at rest (4.25 to 3.98 mmol/l, p less than 0.05) and during exercise (5.18 to 4.87 mmol/l, p less than 0.05) on fosenopril, but rose in subjects on propranolol during exercise (4.99 to 5.44 mmol/l, p less than 0.01). Plasma renin activity rose on fosenopril and fell on propranolol. Plasma aldosterone was uninfluenced by either drug. Fosenopril was well tolerated and its antihypertensive profile is similar to that of beta blockers and other ACE inhibitors.

Control of serum potassium during fasting in patients with end-stage renal disease

In order to evaluate internal potassium balance in patients with end-stage renal disease (ESRD), epinephrine (0.015 micrograms/kg/min) was infused intravenously into normal control (N = 9) and ESRD subjects (N = 7) after a 26 hour fast. Hyperkalemia developed in ESRD patients after 16 hours of fasting, as compared with control subjects (P = 0.02). The hemodynamic response to epinephrine was similar in the two groups. During epinephrine infusion for one hour, the serum potassium decreased in normal subjects, from 4.3 +/- 0.2 mEq/liter to 3.9 +/- 0.1 mEq/liter, but did not change in ESRD patients (P = 0.005). Serum CO2 declined in ESRD, but not in control subjects, while glucose levels were not different in the two groups. Plasma aldosterone was significantly higher in fasting ESRD patients and failed to decrease during epinephrine infusion as compared to controls. Plasma insulin levels remained low in both groups even though serum glucose levels increased. These results demonstrate that hyperkalemia occurs during fasting in ESRD probably as the result of insulinopenia, and suggest that a diminished response to epinephrine may contribute to hyperkalemia.

Beta-adrenergic enhancement of angiotensin II-stimulated aldosterone secretion

Beta-adrenergic agonists have been shown to stimulate aldosterone secretion. Angiotensin II (AII) is one of the important stimuli of aldosterone secretion; conceivably beta-adrenergic influences affect the stimulatory potential of AII. Using cultured rat adrenal capsules, we found that 10(-7) M epinephrine and 10(-7) M isoproterenol enhanced 10(-7) M AII-stimulated aldosterone production. Propranolol (10(-7) M) completely inhibited the ability of epinephrine to augment the stimulatory actions of AII. In conclusion, beta-adrenergic agonists promote stimulation of aldosterone secretion by AII.

Effects of somatostatin and oral potassium administration on terbutaline-induced hypokalemia

Terbutaline, a beta 2-adrenergic agonist, has been shown to cause hypokalemia and an increase of plasma glucose and serum insulin concentrations. We considered that terbutaline-induced hypokalemia may be due to the insulin-induced shift of potassium (K+) from the extracellular to the intracellular space. If so, then inhibition of insulin secretion by somatostatin would prevent terbutaline-induced hypokalemia. Further, we wondered whether oral potassium pretreatment could prevent terbutaline-induced hypokalemia. Therefore, 10 healthy volunteers (5 men, 5 women; mean age, 23 yr +/- 3 SD) received either sodium chloride (NaCl) or somatostatin intravenously together with 0.25 mg terbutaline subcutaneously in a double-blind crossover design. On a third test day, they received 39 mval of K+ powder orally before terbutaline injection in an open trial. Terbutaline caused a significant decrease of K+ (from 3.96 +/- 0.08 to 3.3 +/- 0.13 mmol/L +/- SEM; p less than 0.0005), accompanied by a significant increase in plasma glucose (from 83 +/- 3.6 to 101 +/- 4.4 mg/dl +/- SEM; p less than 0.01) and serum insulin concentrations (from 11.7 +/- 0.9 to 19.9 +/- 1.1 microU/ml +/- SEM; p less than 0.001), confirming earlier data. Somatostatin pretreatment inhibited the terbutaline-induced hypokalemia; the small fall of K+ (from 3.7 +/- 0.08 to 3.5 +/- 0.2 mmol/L) was no longer significant. Insulin secretion was completely blocked by somatostatin, leading to an even more pronounced increase of blood glucose. Hypokalemia after terbutaline injection was not prevented by oral potassium pretreatment. In summary, the present findings confirm that terbutaline-induced hypokalemia is associated with increased plasma glucose and insulin levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of the effects of salbutamol by propranolol and atenolol

Six healthy volunteers were given single oral doses of 8 mg salbutamol, 40 mg propranolol, 100 mg atenolol, 8 mg salbutamol plus 40 mg propranolol and 8 mg salbutamol plus 100 mg atenolol, in a placebo controlled study. Plasma potassium fell following salbutamol and rose following atenolol or propranolol, and the hypokalaemic effect of salbutamol was reversed more effectively by propranolol than by atenolol. Although blood glucose rose after salbutamol, it was unaffected by any of the other treatments. Lying and standing pulse rate rose after salbutamol and fell equally after either beta-adrenoceptor antagonist, and fell more after salbutamol plus propranolol than after salbutamol plus atenolol. Blood pressure rose after salbutamol and fell after each of the other treatments. Forty milligrams propranolol was thus more effective than 100 mg atenolol in reversing the metabolic effects of 8 mg salbutamol, and was as effective in reversing the cardiovascular effects. In cases of symptomatic salbutamol overdose, propranolol should be considered as an antidote provided the patient is not asthmatic.

Effect of myocardial revascularization and vein graft blood flow on pacing function

The effect of myocardial revascularization and vein graft blood flow on pacing function was determined in nine patients undergoing aortocoronary bypass. Pacing variables including threshold, current, and resistance were measured with a pacing system analyzer during intermittent pacing with a transluminal bipolar ventricular pacing probe. Pacing function was analyzed immediately before cardiopulmonary bypass (CPB) and compared with measurements taken eight minutes after full flow through the vein grafts had been established. Comparison of these two times showed a significant decrease in resistance, P < 0.003, and threshold, P < 0.03. After the second measurement, left anterior descending (n = 8), or right coronary (n = 1) vein graft blood flow was interrupted. Pacing variables were analyzed at one minute, two minutes, and four minutes following vein graft clamping; and a final set of measurements was obtained one minute following release of the vein graft clamp. Threshold increased but did not reach statistical significance. Resistance increased significantly: P < 0.03. All values returned to baseline following release of the vein graft clamp and full return of blood flow. The results of this study suggest that pacing function measurements are sensitive to changes in vein graft blood flow and may provide useful information about the condition of the myocardium, especially immediately prior to weaning from CPB.

Effect of various therapeutic approaches on plasma potassium and major regulating factors in terminal renal failure

PURPOSE

The development of life-threatening hyperkalemia poses a risk for patients with chronic preterminal renal failure. Various therapeutic options have been suggested for hyperkalemic emergencies in these patients; to date, however, no study has evaluated the relative efficacies of these measures in the presence of renal failure. Our goal was to examine the acute effects of a variety of therapeutic approaches, as well as those of hemodialysis, on plasma potassium levels in a hemodialysis population.

PATIENTS AND METHODS

Ten patients with terminal renal failure undergoing maintenance hemodialysis were enrolled in the study. Blood gas parameters and plasma sodium, potassium, glucose, osmolality, renin, aldosterone, epinephrine, norepinephrine, dopamine, and insulin were measured before, during, and after 60-minute infusions of bicarbonate, epinephrine, and insulin in glucose, and before, during, and after performance of regular hemodialysis for one hour.

RESULTS

Hypertonic as well as isotonic intravenous bicarbonate (2 to 4 mmol/minute) induced a marked rise in plasma bicarbonate and pH, but failed to lower the plasma potassium level (5.66 versus 5.83 mmol/liter before and after). Epinephrine, 0.05 microgram/kg/minute administered intravenously, decreased plasma potassium only slightly from 5.57 to 5.25 mmol/liter, and five patients showed no decline. On the other hand, insulin in glucose, 5 mU/kg/minute intravenously, effectively lowered plasma potassium levels from 5.62 to 4.70 mmol/liter, and hemodialysis induced the most rapid decline from 5.63 to 4.29 mmol/liter. Plasma aldosterone was elevated before treatment; it correlated with plasma potassium and dropped during intravenous bicarbonate administration or hemodialysis. Pretreatment plasma renin activity, insulin, epinephrine, norepinephrine, and dopamine levels were generally normal.

CONCLUSION

We conclude that in patients with terminal renal failure undergoing maintenance hemodialysis, intravenous bicarbonate is ineffective in lowering plasma potassium rapidly, and epinephrine is effective in only half the patients, whereas insulin in glucose is a fast and reliable form of therapy for hyperkalemic emergencies. Plasma aldosterone levels are appropriate in relationship to plasma potassium levels, and levels of other potassium-influencing hormones are generally normal.

Hypokalemia induced by inhaled bronchodilators

Since parenteral beta 2-adrenergic stimulation can induce hypokalemia, we postulated that administration of beta 2 adrenoreceptor agonists by inhalation could induce the same. We administered the usual clinical doses of three commonly used bronchodilators to each of six subjects receiving assisted mechanical ventilation in line with the ventilator: two beta 2-adrenoreceptor agonists, metaproterenol, 5 percent solution, and isoetharine, 1 percent solution; and the anticholinergic agent atropine as a control. Each bronchodilator was nebulized over 10 to 15 minutes in random order, four hours apart, and given to every subject. Plasma potassium was measured at five-minute intervals and arterial blood gases at 15-minute intervals, for a total of 50 minutes after administration of each bronchodilator. Following administration of each drug, plasma potassium showed an average decline. The mean decline in plasma potassium from baseline was statistically significant for metaproterenol (p = 0.04) and atropine (p = 0.001) but not for isoetharine (p = 0.09). Although there were no statistically significant differences among the declines in plasma potassium induced by the three drugs, metaproterenol caused the greatest decline (-0.6 mEq/L).

The role of aldosterone in potassium tolerance: studies in anephric humans

Since the role of aldosterone in mediating extrarenal potassium transport remains uncertain, the effect of mineralocorticoid on potassium metabolism was assessed in anephric patients. Seven anephric patients underwent three identical 72-hour periods between hemodialyses during which treatment with either 10 mg/day deoxycorticosterone acetate (DOCA) intramuscularly or 300 mg/day spironolactone orally was compared to a baseline control period. The serum potassium rise, plasma aldosterone, salivary and stool electrolytes were measured in response to potassium loading over 48 hours with a metabolic diet containing 38 mEq/day followed by an "acute" oral potassium load of 0.5 mEq/kg. Acute potassium loading with DOCA resulted in a lower increment in serum potassium than with spironolactone (P less than 0.01). The volume of distribution of the acute potassium load at three hours was 55% of body weight with DOCA, which was significantly greater (P less than 0.05) than with either spironolactone (35%) or control (34%). However, with the dietary load of potassium, the increments in serum potassium measured at 24 and 48 hours (13 hours post-prandial) were similar in all three periods. The volume of distribution of the dietary potassium was not altered by DOCA or spironolactone but had risen to an average of 172% at 24 hours and 243% at 48 hours in the three periods. Plasma aldosterone levels were low, positively correlated to the serum potassium and similar in all three periods without evidence of feedback inhibition by DOCA or stimulated by spironolactone.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonoliguric hyperkalemia in the premature infant weighing less than 1000 grams

Eighteen very low birth weight premature infants born before 28 weeks gestation and weighing less than 1000 gm were evaluated prospectively for disturbances in serum electrolyte concentrations and for renal glomerular and tubular functions. Clinically symptomatic hyperkalemia resulting in significant electrocardiographic dysrhythmias developed in eight of these infants; 10 babies remained normokalemic. Peak serum potassium concentration ranged from 6.9 to 9.2 mEq/L in the hyperkalemic group; all potassium values in the normokalemic group were less than 6.6 mEq/L. Indices of renal glomerular function and urine output were similar in both groups; no infant had oliguria. Serum creatinine concentrations were the same in both groups (1.04 +/- 0.16 SD mg/dl in normokalemic vs 1.19 +/- 0.24 mg/dl in hyperkalemic infants, beta less than 0.2 at alpha = 0.05), and glomerular filtration rates did not differ significantly (6.29 +/- 1.78 ml/min/1.73 m2 in normokalemic vs 5.70 +/- 1.94 ml/min/1.73 m2 in hyperkalemic infants, beta less than 0.2 at alpha = 0.05). In contrast, indicators of tubular function revealed a significantly larger fractional excretion of sodium in hyperkalemic infants: 13.9 +/- 5.4% versus 5.6 +/- 0.9% in normokalemic control subjects (p less than 0.001). Hyperkalemic infants also had a tendency toward lower urine concentrations of potassium, although there was no significant difference in their net potassium excretion in comparison with that in the normokalemic group. We speculate that hyperkalemia in the tiny baby is in part the result of immature distal tubule function with a compromise in ability to regulate potassium balance.

Effect of cetamolol on epinephrine-induced hypokalemia

The effect of cetamolol (an investigational cardioselective beta blocker with intrinsic sympathomimetic activity) on the hypokalemic response to epinephrine infusions in normal subjects was evaluated and compared with placebo and two other beta-adrenergic blocking drugs. After two daily doses of cetamolol 15 mg, atenolol (a cardioselective beta blocker) 50 mg; a long-acting propranolol preparation (a nonselective beta blocker) 80 mg; or placebo, 12 men (mean age, 26.7 years) were infused with epinephrine. The resulting average plasma epinephrine level was 1123 pg/mL, whereas average baseline serum potassium levels for the four treatment groups ranged from 3.94 to 4.07 mEq/L. Epinephrine-induced hypokalemia occurred in the placebo group (maximum potassium decrease of 1.00 mEq/L) and in the atenolol group (maximum potassium decrease of 0.59 mEq/L); potassium levels did not decrease but rose slightly in subjects receiving cetamolol or propranolol. Subjects treated with placebo or atenolol also demonstrated statistically significant prolongation of the QTc interval (0.039 seconds with placebo; 0.023 seconds with atenolol) and frequently developed T-wave flattening and U-wave appearance. After pretreatment with cetamolol or propranolol, however, the QTc interval was unaffected, T-wave abnormalities did not occur, and U waves appeared only rarely. The results of this study indicate that cetamolol blocks epinephrine-induced hypokalemia and associated electrocardiographic changes.

Potassium secretion by rat distal colon during acute potassium loading: effect of sodium, potassium intake and aldosterone

1. Potassium secretion by the distal colon before and during intravenous infusion of a potassium load was measured in vivo in groups of rats treated in various ways: A, normal control; B, adrenalectomized; C, sodium depleted; D, on potassium-rich diet for 7 days; E, after 72 h aldosterone (1 microgram/h); F, after 72 h aldosterone (10 micrograms/h). 2. Potassium infusion produced no increase of secretion in the adrenalectomized rats but in all the other groups it increased by 2- to 3-fold. Secretion during infusion correlated well with the basal (pre-infusion) rate and in groups C and D reached 140 +/- 15 and 173 +/- 17 nmol min-1 cm-1 respectively compared with 28 +/- 6 nmol min-1 cm-1 in the controls (A). The passive paracellular pathway for potassium was unaffected by the infusion. Amiloride (100 mumol/l) did not significantly affect potassium secretion rate either before or during the acute potassium infusion. The potassium channel blocker, tetraethylammonium chloride, reduced both basal and the secretion rate during infusion. 3. Transepithelial potential difference (PD), active sodium absorption and sodium fluxes were similar in normal controls and rats fed the potassium-rich diet. However, the PD was partially amiloride sensitive in the latter group although amiloride insensitive in the normal group. In sodium-depleted rats, the PD was elevated and totally amiloride insensitive. 4. In both aldosterone-treated groups (E and F), basal potassium secretion rate was high and similar, and during potassium infusion rose 3-fold to 114 +/- 24 (E) and 105 +/- 5 (F) nmol min-1 cm-1. However, the PD was not elevated significantly in group E and was only partially amiloride sensitive, whereas in those infused at the higher rate (F) the PD was increased and was totally amiloride sensitive. 5. The high potassium secretion rates developed by this epithelium in sodium-restricted and potassium-enriched dietary states appear to depend on the presence of an amiloride-insensitive transcellular potassium pathway which is induced at a lower level of aldosterone stimulation than is the amiloride-sensitive transcellular sodium pathway.

Changes in intracellular ion activities induced by adrenaline in human and rat skeletal muscle

To study the stimulating effect of adrenaline (ADR) on active Na+/K+ transport we used double-barrelled ion-sensitive micro-electrodes to measure the activities of extracellular K+ (aKe) and intracellular Na+ (aNai) in isolated preparations of rat soleus muscle, normal human intercostal muscle and in one case of hyperkalemic periodic paralysis (h.p.p.). In these preparations, bath-application of ADR (10(-6) M) resulted in a membrane hyperpolarization and transient decreases aKe and aNai which could be blocked by ouabain (3 x 10(-4) M). In the h.p.p. muscle a continuous rise of aNai induced by elevation of aKe to 5.2 mM could be stopped by ADR. In addition, the intracellular K+ activity (aKi), the free intracellular Ca2+ concentration (pCai) and intracellular pH (pHi) were monitored in rat soleus muscle. During ADR aKi increased, pHi remained constant and intracellular Ca2+ apparently decreased. In conclusion, our data show that ADR primarily stimulates the Na+/K+ pump in mammalian skeletal muscle. This stimulating action is not impaired in the h.p.p. muscle.

Changes in serum potassium concentration with exercise in Hereford calves: effects of adrenalectomy

1. Serum potassium concentration [K+] was measured pre- and postadrenalectomy in three Hereford steer calves before, during and following 3.5 min exercise at their maximal speed capability. 2. Both before and after adrenalectomy, serum [K+] increased an average of 2.4 mEq.1(-1) during exercise and was at control levels 10 min postexercise. 3. Hormones from neither the adrenal cortex nor the adrenal medulla influence serum [K+] dynamics during acute exercise.

Effects of salbutamol and hyperventilation on the rise in serum potassium after succinylcholine administration

It is known that circulating catecholamines stimulating beta 2-receptors and the acid-base balance play important roles in the regulation of serum potassium (K+). The present study was undertaken to investigate the effect of salbutamol (SB), a highly selective beta 2 agonist, and hyperventilation (HV)-induced alkalosis on the change in serum K+ after succinylcholine (SCh) administration in dogs. Pretreatment with SB (0.4 microgram.kg-1.min-1 for 30 min) produced sustained decreases in serum K+ and mean arterial pressure, and transient increases in cardiac output and serum insulin concentration. Maintaining respiratory alkalosis with HV (PaCO2 = 2.6-3.3 kPa) produced sustained decreases in serum K+ and cardiac output. Although both pretreatment with SB and HV-induced alkalosis significantly reduced the absolute increases in serum K+ after SCh, the effect of SB was more remarkable than that of HV. These results suggest that the degree of beta 2-receptor activity can strongly modulate the change in serum K+ after SCh administration.

Potassium homeostasis and hypokalemia

Potassium, largely an intracellular cation, contributes to the regulation of cellular volume, to tissue growth and metabolic synthesis of proteins and nucleic acids, and to the integrity of electrical properties of excitable tissues as well as nonexcitable, transporting epithelia. Potassium balance is closely regulated by a variety of nonrenal and renal mechanisms. When potassium losses are sufficient to induce hypokalemia, either through nonrenal or renal causes, profound adverse effects on neuromuscular, cardiac, vascular, and renal tissues may ensue. The diagnostic approach is straightforward, and therapy must be directed to replenish losses without inducing a rapid, excessive, and potentially fatal increase in the potassium concentration of the serum.

Immediate and long-term pathophysiologic mechanisms underlying the genesis of sudden cardiac death in patients with congestive heart failure

Congestive heart failure is the most important predisposing factor to the occurrence of sudden death in patients with cardiovascular disease. As left ventricular dysfunction deteriorates and symptoms of heart failure become evident, ambulatory ventricular arrhythmias become increasingly frequent and complex, and sudden cardiac death becomes an increasingly common occurrence. When the left ventricular ejection fraction has declined to less than 30 percent and symptoms of heart failure become refractory to treatment with digitalis and diuretics, 35 to 50 percent of patients will die of a lethal cardiac arrhythmia within three years. A number of factors interact to determine the occurrence of malignant ventricular arrhythmias in patients with congestive heart failure. Myocardial fibrosis and enhanced left ventricular wall stress may alter the electrophysiologic properties of the myocardium, but these factors may not be sufficient to explain the development of lethal rhythm disturbances. Neurohormonal activation may exacerbate the frequency and complexity of ambulatory arrhythmias in these patients, but such activation can persist for long periods without fatal electrophysiologic sequelae. Recent investigations suggest that electrolyte depletion may provide an important immediate precipitating cause for the occurrence of fatal ventricular tachyarrhythmias in the patient with severe left ventricular dysfunction whose susceptibility is markedly heightened by preexisting structural, hemodynamic, or neurohormonal factors. Further work is needed to determine if prophylactic therapy directed at preventing electrolyte depletion can favorably modify the long-term outcome of these severely ill patients.

Beta-adrenoceptor blockade and suxamethonium-induced rise in plasma potassium

The effects of beta-adrenergic blockade on the suxamethonium-induced rise in arterial plasma potassium were studied in patients who presented for open heart surgery. No potentiation of the immediate rise in plasma potassium was observed.

Adrenergic modulation of potassium metabolism during exercise in normal and diabetic humans

The effect of acute and chronic beta- and alpha-adrenergic blockade on potassium homeostasis during moderate intensity exercise (40% VO2max) was investigated in control and insulin-dependent diabetic subjects. In protocol I, subjects were studied during exercise alone, exercise plus intravenous propranolol, and exercise plus intravenous phentolamine. In both the control and diabetic groups, exercise alone produced a modest increase in the plasma potassium concentration (0.31 +/- 0.06 meq/l), while propranolol exacerbated this hyperkalemic response. In contrast, the increment in plasma potassium during phentolamine was similar to exercise alone in normals but was 26% (P less than 0.05) lower in the diabetic group. In protocol II, the effect of chronic (5 days) beta-adrenergic blockade on potassium homeostasis was examined. Subjects participated in three studies: exercise alone, exercise plus propranolol (beta 1/beta 2-antagonist), and exercise plus metoprolol (beta 1 antagonist). In the nondiabetic group, both propranolol and metoprolol were associated with a 40% greater increase in potassium compared with exercise alone. In the diabetic group, propranolol, but not metoprolol, was associated with a deterioration in potassium tolerance. In no study could the alterations in potassium homeostasis be explained by a change in urinary potassium excretion. In summary, alpha-adrenergic blockade ameliorates exercise-induced hyperkalemia in diabetic but not in control subjects, nonspecific beta-adrenergic blockade causes a greater increment in potassium when compared with exercise alone, and specific beta 1-adrenergic blockade exacerbates exercise-induced hyperkalemia in control, but not in diabetic subjects. These results indicate that both alpha- and beta-adrenergic regulation of extrarenal potassium metabolism is altered in insulin-dependent diabetes mellitus.

Hypotension and sinus arrest with exercise-induced hyperkalemia and combined verapamil/propranolol therapy

A case of life-threatening hypotension due to sinus arrest is described in a patient in whom exercise-induced hyperkalemia developed during a stable regimen that included verapamil, propranolol, and ibuprofen. Renal and extrarenal handling of the endogenous potassium load induced by heat and exertion in this patient may have been compromised by the presence of ibuprofen and propranolol. When superimposed upon the negative chronotropic effects of verapamil and propranolol, the hyperkalemia precipitated sinus arrest. Clinicians should be aware of this potential metabolic-drug interaction in patients taking verapamil and/or propranolol who perform strenuous exercise in hot weather or who may be exposed to other hyperkalemic precipitants.

Hormone-electrolyte interactions in the pathogenesis of lethal cardiac arrhythmias in patients with congestive heart failure. Basis of a new physiologic approach to control of arrhythmia

Congestive heart failure is the most arrhythmogenic disorder in cardiovascular medicine. As left ventricular performance deteriorates and symptoms of dyspnea and fatigue become progressively more severe, nearly all patients with heart failure experience frequent and complex ventricular tachyarrhythmias and nearly half die suddenly during long-term follow-up. This imminent risk of sudden death appears to be present for all patients with congestive heart failure; ambulatory electrocardiographic monitoring and programmed electrical stimulation are not useful in distinguishing patient subsets that are particularly predisposed to fatal arrhythmic events. Although conventional antiarrhythmic agents are widely prescribed as a nonspecific approach to prevent sudden death in these patients, there is little evidence to indicate that these drugs possess clinically important antiarrhythmic activity in patients with congestive heart failure, and these agents frequently serve to exacerbate the heart failure state and the underlying ventricular tachyarrhythmia. A useful approach to the prevention of sudden death in patients with congestive heart failure addresses the reversible causes of lethal ventricular arrhythmias in these individuals. Both experimental and clinical evidence indicates that circulating neurohormones and electrolyte deficits (particularly of potassium and magnesium) interact to provoke malignant ventricular ectopic rhythms and that the prevention of electrolyte depletion and the use of neurohormonal antagonists may exert clinically important antiarrhythmic actions. This physiologic approach may prove to be a more effective means of ameliorating the problem of sudden death than the empiric administration of conventional antiarrhythmic drugs.

Initial therapy for mild hypertension

The treatment of mild hypertension has been a subject of controversy because its benefits versus risks are not as well established as they are for moderate to severe hypertension. Results of several studies, however, now show that treatment reduces the frequency of stroke in those with milder blood pressure elevations. New guidelines published by the Joint National Committee recommend that treatment of mild hypertension begin with either a diuretic or a beta blocker. The effect on the most common complication of mild hypertension, that is, coronary heart disease (myocardial infarction and sudden cardiac death), has, however, not been encouraging in studies in which diuretics have been used as first-line treatment. Two large-scale primary preventive studies compared the efficacy of diuretics and beta blockers in reducing coronary heart disease in hypertensive patients; results were in favor of beta blocker regimens in men. So far there is some evidence, but no hard scientific proof, that certain beta blockers offer advantages over diuretics in preventing myocardial infarction and sudden cardiac death in hypertensive patients. A major concern with the use of diuretics is the risk of hypokalemia; this can be reduced when they are combined with beta blockers.

Ventricular arrhythmias in patients with myocardial infarction and ischaemia. The role of serum potassium

An association between low serum potassium concentrations and ventricular arrhythmias has been observed by a number of investigators in patients with both acute myocardial infarction and symptomatic angina. The increased frequency of ventricular fibrillation in patients with low serum potassium concentrations has not been attributable to differences in the size or location of the infarct or concomitant digitalis administration. Although prior diuretic usage is frequently associated with a low serum potassium concentration, diuretic usage in the absence of significant changes in serum electrolytes is not associated with an increase in malignant ventricular arrhythmias. It is not clear whether the alterations in serum potassium are important in the pathogenesis of the arrhythmias or merely a marker for other arrhythmogenic factors. To the extent that changes in serum potassium contribute to the production of serious ventricular arrhythmias, efforts should be directed at the correction of such electrolyte disturbances. Attempts to increase the serum potassium in acute cases do not appear to be successful in preventing ventricular arrhythmias in this setting. Primary prevention of electrolyte disturbances would seem to offer more effective protection against serious arrhythmias. Long term studies with beta-blockers support this premise.

Hypokalemia from beta 2-receptor stimulation by circulating epinephrine

Beta 2-receptor stimulation is required for catecholamine-induced hypokalemia to occur. This hypokalemia is not mediated by insulin, renin or aldosterone. Catecholamine-induced hypokalemia can be prevented by selective beta 2 blockade, which does not abolish the inotropic effect of epinephrine.

Prevention of epinephrine-induced hypokalemia by nonselective beta blockers

Experimental evidence is presented that activation of beta 2 adrenoreceptors causes a dose-dependent decrease in plasma potassium, probably by shifting potassium into the cell. By this mechanism epinephrine may cause hypokalemia and predispose to cardiac arrhythmias. Prevention of these effects by nonselective beta blockers may contribute to the cardioprotective action of these drugs.