Adrenergic modulation of extrarenal potassium disposal

Effect of norepinephrine on swelling-induced potassium transport in duck red cells. Evidence against a volume-regulatory decrease under physiological conditions

Duck red cells exhibit specific volume-sensitive ion transport processes that are inhibited by furosemide, but not by ouabain. Swelling cells in a hypotonic synthetic medium activates a chloride-dependent, but sodium-independent, potassium transport. Shrinking cells in a hypertonic synthetic medium stimulates an electrically neutral co-transport of [Na + K + 2 Cl] with an associated 1:1 K/K (or K/Rb) exchange. These shrinkage-induced modes can also be activated in both hypo- and hypertonic solutions by beta-adrenergic catecholamines (e.g., norepinephrine). Freshly drawn cells spontaneously shrink approximately 4-5% when removed from the influence of endogenous plasma catecholamines, either by incubation in a catecholamine-free, plasma-like synthetic medium, or in plasma to which a beta-receptor blocking dose of propranolol has been added. This spontaneous shrinkage resembles the response of hypotonically swollen cells in that it is due to a net loss of KCl with no change in cell sodium. Norepinephrine abolishes the net potassium transport seen in both fresh and hypotonically swollen cells. Moreover, cells swollen in diluted plasma, at physiological pH and extracellular potassium, show no net loss of KCl and water ("volume-regulatory decrease") unless propranolol is added. Examination of the individual cation fluxes in the presence of catecholamines demonstrates that activation of [Na + K + 2Cl] co-transport with its associated K/Rb exchange prevents, or overrides, swelling-induced [K + Cl] co-transport. These results, therefore, cast doubt on whether the swelling-induced [K + Cl] system can serve a volume-regulatory function under in vivo conditions.

The effect of intravenously administered salbutamol on serum potassium in asthmatic and nonasthmatic atopic subjects

The role of adrenergic mechanism in the pathogenesis of allergic disease is controversial. Recent experimental and clinical reports have suggested that beta-adrenergic blockade impairs and beta stimulation enhances extrarenal potassium uptake in humans. This led us to study the effect of the intravenous administration of salbutamol, a specific beta-2-adrenergic agonist, on serum potassium in 9 healthy subjects and in 23 patients with allergic asthma and/or rhinitis. Serum potassium fell significantly and reached a peak decline at the end of venous infusion in all the normal subjects. Seventeen atopic subjects showed a lower or absent serum K+ decrement: there was no difference between asthmatic and rhinitic patients. There was no relation among the salbutamol-induced serum potassium decrement, serum glucose increment, blood pressure and heart-rate changes, and nonspecific bronchial reactivity. These findings suggest that beta-2-adrenergic hyporesponsiveness is present only in some allergic patients.

Effect of timolol on changes in serum potassium concentration during acute myocardial infarction

One hundred and six patients with acute myocardial infarction admitted to hospital within four hours after the onset of symptoms were randomised to treatment with intravenous timolol (54 patients) or placebo (52 patients). Serum potassium concentrations were estimated at frequent intervals during the first 24 hours of admission. Patients in both treatment groups, who did not receive subsequent diuretic treatment, had a transient rise in serum potassium concentration, which was maximal after four hours. This rise was abolished by diuretic treatment in the placebo group but not in the timolol group, in which there was a pronounced and prolonged rise in serum potassium concentration. The change in serum potassium concentration in the first four hours after admission correlated with cumulative creatine kinase release in the placebo group, but not in the timolol group. Hypokalaemia (serum potassium concentration less than or equal to 3.5 mmol/l) occurred in 15 (28.8%) patients in the placebo group and in seven (13%) in the timolol group and was independent of infarct size. The frequency of hyperkalaemia was not increased in the timolol group. By increasing the serum potassium concentration and preventing hypokalaemia, the use of intravenous timolol early in acute myocardial infarction may have important clinical effects in addition to reducing infarct size.

Catecholamine modulation of rapid potassium shifts during exercise

Plasma potassium rises during muscular exercise and falls rapidly when exercise is stopped. Since the sympathoadrenal system is stimulated with exertion and both alpha- and beta-adrenergic agonists affect internal potassium homeostasis, we studied the influence of catecholamines on potassium shifts during and after exercise. Six healthy subjects were given maximal exercise stress tests under three conditions: with no medication (control), during beta-blockade with propranolol, and during alpha-blockade with phentolamine. Compared with a peak rise in plasma potassium of 1.23 +/- 0.27 mmol per liter (mean +/- S.E.M.) during the control study, propranolol caused a rise of 1.89 +/- 0.35 (P less than 0.01) and a sustained elevation during recovery. Phentolamine diminished the rise of potassium (0.70 +/- 0.21 mmol per liter; P less than 0.01) and lowered the potassium level throughout recovery. These effects of catecholamines were independent of the venous pH, the plasma bicarbonate and serum glucose levels, and urinary potassium excretion, and they did not appear to be due to insulin. High norepinephrine and epinephrine levels confirmed the release of catecholamines capable of stimulating alpha- and beta-receptors. Exercise work did not differ among the groups. beta-Adrenergic receptors appear to moderate the acute hyperkalemia of exercise, whereas alpha-adrenergic receptors act to enhance hyperkalemia and may protect against hypokalemia when exertion ceases.

Hyperkalemia complicating digoxin toxicity in a patient with renal failure

We describe the occurrence of hyperkalemia in a stable hemodialysis patient who developed digoxin toxicity. The patient had been receiving digoxin for 2 years. His maintenance digoxin dose was increased from 0.125 to 0.25 mg three times a week, which resulted in a toxic serum level of 4.9 ng/mL (therapeutic range is 0.8 to 2.0 ng/mL). As a consequence of the digoxin toxicity, he became hyperkalemic (7.8 mEq/L), and this value returned to normal only after the digoxin level was lowered by a combination of oral charcoal and dialysis. This study shows how readily hyperkalemia can occur in an anephric patient manifesting digoxin toxicity. Thus, potentially lethal hyperkalemia can occur in hemodialysis patients who ingest therapeutic quantities of digoxin. Digoxin toxicity should be added to the differential diagnosis of hyperkalemia in patients with renal failure. This can occur despite the absence of a history of massive ingestion of a cardiac glycoside.

Potassium homeostasis and clinical implications

The clinical estimation of potassium balance generally depends on the level of serum potassium. Since the extracellular fluid contains only 2 percent of the total body potassium, it must be recognized that potassium deficits are usually large before significant hypokalemia occurs, whereas smaller surfeits of potassium will cause hyperkalemia. The total body potassium is regulated by the kidney in which distal nephron secretion of potassium into the urine is enhanced by aldosterone, alkalosis, adaptation to a high potassium diet, and delivery of increased sodium and tubular fluid to the distal tubule. However, the distribution of potassium between the intracellular and extracellular fluids can markedly affect the serum potassium level without a change in total body potassium. Cellular uptake of potassium is regulated by insulin, acid-base status, aldosterone, and adrenergic activity. Hypokalemia, therefore, may be caused by redistribution of potassium into cells due to factors that increase cellular potassium uptake, in addition to total body depletion of potassium due to renal, gastrointestinal, or sweat losses. Similarly hyperkalemia may be caused by redistribution of potassium from the intracellular to the extracellular fluid due to factors that impair cellular uptake of potassium, in addition to retention of potassium due to decreased renal excretion. An understanding of the drugs that affect potassium homeostasis, either by altering the renal excretion of potassium or by modifying its distribution, is essential to the proper assessment of many clinical potassium abnormalities. Both hypokalemia and hyperkalemia may cause asymptomatic electrocardiographic changes, serious arrhythmias, muscle weakness, and death. Hypokalemia has also been associated with several other consequences, including postural hypotension, potentiation of digitalis toxicity, confusional states, glucose intolerance, polyuria, metabolic alkalosis, sodium retention, rhabdomyolysis, intestinal ileus, and decreased gastric motility and acid secretion.

Endocrine physiology of electrolyte metabolism

Historically, the sodium ion has been given prominence in relation to cardiovascular disease, perhaps to the exclusion of other ions. Recently, other ions, including chloride, potassium, magnesium and calcium have received increasing attention in relation to hypertension, cardiac arrhythmias, and metabolic derangements. Endocrine factors controlling these ions have also received increasing attention; they include classic hormonal actions as well as neurotransmission and paracrine hormonal actions. Studies indicate that control of the renin-angiotensin-aldosterone system resides in cytosolic calcium ion levels in the juxtaglomerular cell, as well as chloride ion and prostaglandins at the macula densa. Renin release is stimulated by hyperpolarisation of the juxtaglomerular cell induced by beta 1-agonists, parathyroid hormone, glucagon, magnesium and low cytosol calcium. Renin release is inhibited by high calcium, potassium and angiotensin II. Subsequent to renin release, hormonal regulation includes stimulation of converting enzyme activity by cortisol and prostaglandin (PGE2). Other hormonal control includes antidiuretic hormone producing dilution of extracellular electrolytes and augmented peripheral resistance. A recently identified natriuretic factor isolated from cardiac atria appears to be a potent diuretic with actions similar to that of frusemide (furosemide). Other electrolytes have received closer scrutiny. Chloride may play a dominant role in renal sodium reabsorption, responding to prostaglandin levels. Calcium has been recognised as a basic regulator of the secretion of such hormones as noradrenaline, renin, and aldosterone. As well, calcium ion changes are the means by which smooth muscle contraction is effected. Parathyroid hormone and vitamin D regulate the level of this ion in the body. In addition, a high dietary calcium intake appears to play a protective role against hypertension, while calcium channel blockers appear to reduce blood pressure. Endocrine systems play a major role in the protection against acute elevations in serum potassium by means of insulin action and adrenergic modulation of extrarenal potassium disposal. Aldosterone is recognised as the delayed regulator of potassium excretion. Magnesium levels fall in hyperaldosteronism, hyperparathyroidism, and diabetic keto-acidosis, as well as in malnutrition states. A coexisting potassium deficiency may be refractory to therapy until hypomagnesaemia is corrected. The integrated action of these hormones and electrolytes are thus of major importance in regulation of the cardiovascular system.

Impairment of extrarenal potassium disposal by alpha-adrenergic stimulation

Since beta-adrenergic stimulation enhances extrarenal potassium uptake, we postulated an opposite effect of the alpha-adrenergic nervous system. Seven healthy subjects were given intravenous potassium chloride (0.5 mmol per kilogram of body weight), in the presence and absence of the alpha-agonist phenylephrine. After potassium chloride alone, the potassium level rose to 0.64 +/- 0.03 mmol (mean +/- S.E.M.); phenylephrine augmented the rise (0.93 +/- 0.09 mmol, P less than 0.025) and prolonged it, without changing urinary potassium excretion. Subsequent administration of potassium and phenylephrine together with the alpha-antagonist phentolamine blocked the rise in the potassium level due to phenylephrine and shortened the duration of elevation, again without affecting urinary potassium excretion. No changes in plasma renin and aldosterone levels or in serum insulin concentrations occurred, to account for these findings. Stimulation of alpha-adrenergic receptors impairs extrarenal disposal of an acute potassium load--the opposite effect of beta-adrenergic stimulation. The alpha-adrenergic effect may act to preserve a normal serum potassium level or may contribute to hyperkalemia under certain circumstances, such as vigorous exercise.

Succinylcholine, cholinoceptors and catecholamines: proposed mechanism of early adverse haemodynamic reactions

An hypothesis is proposed to account for the occurrence of adverse haemodynamic reactions to succinylcholine. Interaction of succinylcholine with cholinergic receptors is postulated to result in release of endogenous catecholamines (predominantly norepinephrine). The occurrence and the clinical manifestations of the adverse reactions would be dependent on the extent of the release. Based on literature reports of findings in experimental animals with nicotinic and muscarinic agents, a mechanism for the release of norepinephrine is outlined. Interaction of succinylcholine with muscarinic and nicotinic receptors is proposed to result in an initial activation which is followed by a phase of chemical insensitivity. Activation of the presynaptic nicotinic receptors on the postganglionic sympathetic terminals leads to a short-lasting release of norepinephrine. Activation of the presynaptic muscarinic receptors produces attenuation of the norepinephrine release. In the majority of patients these opposing actions are balanced and the net result is small, variable, and of little clinical importance. An unbalanced response leading to clinical manifestations can be expected if the two types of the presynaptic cholinoceptors are differentially activated.

Potassium tolerance and bronchial reactivity in asthmatic and nonasthmatic atopic subjects

Abnormal autonomic nervous system responsiveness may contribute to the pathogenesis of allergic diseases. Therefore, we measured the beta-adrenergic systemic (metabolic) responsiveness by means of acute potassium load in 10 normal healthy subjects and in 19 patients with allergic asthma and/or rhinitis. Ten allergic patients showed a greater potassium increment, as in normal subjects, when potassium was infused in the presence of propranolol. There was no difference between asthmatic and rhinitic patients. We then examined the relation between the response to potassium tolerance and the nonspecific, nonpharmacological bronchial reactivity in response to inhalation of ultrasonically nebulized distilled water. Some allergic patients showed bronchial hyperreactivity, while others did not show a difference compared with the controls; there was no significant difference between asthmatics and rhinitics, and there was no relation between nonspecific bronchial reactivity and potassium load tolerance. These findings suggest that systemic beta-adrenergic hyporesponsiveness may be present only in some allergic patients. There is no demonstrable relation among atopic state, nonspecific, nonpharmacological bronchial reactivity, and systemic beta-adrenergic hyporesponsiveness.

A comparison of prazosin versus nadolol in combination with a diuretic

The comparative efficacy and effects on total body potassium of prazosin and polythiazide vs nadolol and polythiazide in the treatment of patients with mild to moderate essential hypertension unresponsive to diuretic alone were compared in an open, crossover trial involving 20 male patients. Both prazosin and nadolol reduced blood pressure to goal values in both study phases. Side effects were minor, and only 1 patient dropped out of treatment for reasons unrelated to the study drugs. Neither prazosin nor nadolol in combination with thiazide had significant additional adverse effects on total body potassium. These findings confirm that the efficacy of prazosin is equivalent to that of nadolol in the long-term management of patients with essential hypertension.

Lack of influence of beta adrenergic blockade on serum potassium during an infusion of potassium

The extent to which the serum potassium rose in a group of six healthy volunteers during an intra-venous infusion of potassium was identical following pretreatment with placebo, low or high dose propranolol and low or high dose metoprolol. Thus in this acute study, we were unable to demonstrate any influence of either selective or non-selective beta adrenergic blockade upon potassium uptake mechanisms. This is in contrast to the effects of beta blockers on potassium reuptake rates noted after exercise and during cardiac surgery.

Hypokalemia from beta2-receptor stimulation by circulating epinephrine

To determine whether epinephrine-induced hypokalemia is due to beta2-adrenoceptor stimulation, and whether hypokalemia can occur at physiologic concentrations of the agonist, epinephrine was infused into six normal volunteers at a rate of 0.1 microgram per kilogram of body weight per minute. The circulating epinephrine concentration was increased to 1.74 +/- 0.65 ng per milliliter, plasma potassium was reduced by 0.82 +/- 0.19 meq per liter, plasma insulin fell by 12 +/- 4 mU per liter, plasma renin activity was elevated, and tachycardia occurred. Isoproterenol infused at 0.02 micrograms per kilogram per minute caused similar tachycardia (25 beats per minute) and elevation in plasma renin activity (6.0 to 6.5 ng per milliliter per hour), but no hypokalemia. The difference in responses to the two catecholamines was ascribed to the relative beta2-selectivity of epinephrine. This hypothesis was tested in six subjects given infusions of epinephrine (0.05 micrograms per kilogram per minute) after administration of either 2.5 or 5 mg of ICI 118551--a selective beta2-receptor antagonist--or placebo. After placebo, epinephrine infusion elevated the circulating epinephrine concentration and reduced plasma potassium; hypokalemia was prevented by the beta2-antagonist. This drug only partially inhibited the rises in plasma renin and glucose and the shortening of systolic time intervals; there was no tachycardia. Fifteen-fold to 30-fold increases in circulating epinephrine concentration appear to cause hypokalemia by a specific beta2-receptor effect distinct from other actions of epinephrine. This phenomenon may be of physiologic importance after severe myocardial infarction, when similar increases in plasma epinephrine have occurred.

Death in ventricular fibrillation induced by isoproterenol in DOCA-salt pretreated rats preceded by changes in myocardial electrolytes

Serum and tissue content of sodium, potassium, magnesium and calcium was determined in controls and desoxycorticosterone acetate (DOCA)-salt treated rats to determine whether electrolyte changes preceded the development of isoproterenol-induced death in ventricular fibrillation. Control Sprague Dawley, male rats, were injected subcutaneously (s.c.) with either saline (Group A) or actinomycin D (0.1 mg/kg; Group B) once daily for 4 days. Other rats received 20 mg of DOCA by implantation, drank normal saline and were injected with either saline (Group C) or actinomycin D (Group D) once daily for 4 days. In the first part of the experiment, it was determined that none of 15 rats from Group C died when challenged with isoproterenol (150 micrograms/kg, s.c.) six days later: however, 13 out of 15 rats from Group D died within 29.1 +/- 15.0 minutes (mean +/- S.D.) from isoproterenol injection. Myocardial sodium was elevated (48.8 +/- 3.8 versus 36.3 +/- 1.9) and potassium decreased (60.4 +/- 3.4 versus 70.6 +/- 3.3, meq/kg wet weight, mean +/- S.D.) in rats that had succumbed to isoproterenol. In the second part of the experiment serum and tissues were removed from control and DOCA-saline pretreated rats before they died in ventricular fibrillation, 20 minutes after isoproterenol. DOCA-saline pretreated rats were hypernatremic and hypokalemic and exhibited higher sodium and lower potassium in skeletal muscle than control rats. Isoproterenol elicited hypokalemia in all rats, but it only elevated sodium and decreased potassium content in the myocardium of rats of Group D, that were more prone to die in ventricular fibrillation. It is concluded that myocardial electrolyte changes precede the onset of ventricular fibrillation and may be associated with the development of this dysrhythmia.

Double-blind comparison between propranolol and bendroflumethiazide in captopril-treated resistant hypertensive patients

In a double-blind crossover trial, 15 captopril (daily dose 600 mg) treated patients received in addition to the converting enzyme inhibitor, placebo, propranolol (240 mg), or bendroflumethiazide (7.5 mg). Propranolol produced an additional hypotensive effect, while pulse rate slowed, indicating effective beta-adrenoceptor blockade. Plasma renin activity decreased, but the hypotensive effect of propranolol was not accompanied by changes in the plasma angiotensin II and aldosterone levels or in the urinary aldosterone excretion. Also bendroflumethiazide lowered blood pressure, while body weight decreased slightly. During captopril-bendroflumethiazide treatment, serum sodium and potassium decreased while the plasma renin-angiotensin-aldosterone system was stimulated. In these captopril-treated patients, the hypotensive response to bendroflumethiazide tended to be somewhat larger than the response to propranolol, but the difference was small and statistically not significant.

Beta-adrenoceptor blocking drugs: adverse reactions and drug interactions

Beta adrenoceptor blocking drugs are relatively well tolerated and adverse reactions to them are not common. The ones that do occur are reviewed in this paper under the following headings: Short term adverse reactions, drug interactions, long term adverse reactions, risks in pregnancy and hazards of abrupt withdrawal. Predictable short term effects may be caused either by the actions of these drugs on the beta 1- or beta 2-receptors. The beta 1 adverse effects are hypotension, bradycardia and cardiac failure; these are best avoided by not giving beta-adrenoceptor blocking drugs to susceptible patients with cardiac disease. The beta 2 adverse effects on the bronchi, the peripheral arteries and various metabolic functions may be reduced to some extent by using a relatively cardioselective drug. Unpredictable short term effects such as fatigue, sexual dysfunction and gastrointestinal symptoms may occur but are not common problems with this group of drugs. Similarly, serious drug interactions are infrequent. Under the heading of long term adverse effects the practolol problem and the risk of causing malignant disorders have been considered. There is no evidence that any of the currently available drugs will cause either a practolol syndrome or malignant disease in man. However, the need for careful appraisal by drug regulatory bodies and continued vigilance by all prescribers of beta-adrenoceptor blocking drugs remains. The possible adverse effects of treatment during pregnancy are also considered. It now appears that beta-adrenoceptor drugs can be used safely in pregnancy but since neonatal bradycardia and hypoglycemia may occur, care should be taken to look for these complications. A serious deterioration may occur when beta-adrenoceptor drugs, given to patients with significant ischemic heart disease, are suddenly stopped. This is a rare occurrence but prescribers should be aware of it.

Long-term beta-receptor blockade--adrenergic and metabolic response to surgery and neurolept anaesthesia

Twenty-six patients on chronic (greater than 3 months) beta-receptor blocking therapy due to ischaemic heart disease and/or hypertension were randomly distributed to a 4-day gradual withdrawal (n = 13) or a continuation of ordinary therapy until a planned cholecystectomy under neurolept anaesthesia (n = 13). Plasma-adrenaline, -noradrenaline, -potassium, -glycerol, -FFA, -insulin and b-glucose were determined perioperatively. The metabolic response to surgery was as expected with hyperglycaemia and depressed insulin levels, which did not differ significantly between the two groups of patients. Plasma-catecholamines showed the highest mean values during emergence from anaesthesia. Plasma-adrenaline and -potassium were constantly highest in the beta-receptor-blocked patients, who also showed indices of a relatively depressed lipolysis compared to patients in whom beta-receptor blockers had been withdrawn. These discrepancies between withdrawal versus continuation of preoperative beta-receptor blockade seemed to be of small clinical importance and did not oppose the present view that beta-receptor blockers should generally be continued during surgery. However, findings in individual patients suggest that beta-receptor blockade may maintain hypoglycaemia in catabolic patients.

Potassium homeostasis during hyperinsulinemia: effect of insulin level, beta-blockade, and age

The euglycemic glucose clamp technique was used to evaluate the influence of level and duration of hyperinsulinemia, presence of beta-adrenergic blockade, and subject age on insulin-mediated changes in plasma potassium. In 16 young subjects, 2-h insulin infusions at 20 (n = 6), 80 (n = 13), and 200 (n = 8) mU.m-2.min-1 resulted in dose-dependent declines in plasma potassium (P less than 0.001 at all doses) during the 1st h. During the 2nd h plasma potassium declined during the 20 mU.m-2.m-1 infusions, was stable during the 80 mU.m-2.m-1 infusions, and rose slightly during the 200 mU.m-2.min-1 infusions. There was a significant reciprocal relationship between the changes in plasma potassium during the 1st and 2nd h of study (r = 0.99, P less than 0.01). During 4-h infusions (80 mU.m-2.min-1, n = 6) plasma potassium declined during the first 90 min (p less than 0.001) and rose thereafter until the end of the infusion (P less than 0.05). Studies with and without propranolol infusion at two insulin dose levels (20 and 80 mU.m-2.min-1) in six young subjects showed no effect of beta-blockade, and studies at three insulin dose levels [20 (n = 5), 80 (n = 6), and 200 (n = 6) mU.m-2.min-1 in 10 older males (63-77 yr] showed no effect of age on the changes in plasma potassium during hyperinsulinemia. These results suggest the presence of a regulatory mechanism influencing insulin-mediated alterations in plasma potassium. This mechanism appears uninfluenced by age or beta-adrenergic blockade.

Disorders of body fluids, sodium and potassium in chronic renal failure

A stable volume and composition of extracellular fluid are essential for normal functioning of the body. Since the kidney is primarily responsible for regulating extracellular fluid, loss of kidney function should have catastrophic consequences. Fortunately, even with loss of more than 90 percent of renal function, a remarkable capacity to regulate body fluid volumes and sodium and potassium persists. Nevertheless, this capacity is limited to chronic renal disease and this has important consequences for clinical management of these patients. How can sodium and potassium homeostasis be assessed? Methods for evaluating the steady-state regulation of sodium include measurement of body fluids and their distribution in different compartments and measurement of exchangeable and intracellular sodium. Short-term regulation of body sodium can be assessed from measurement of sodium balance during changes in dietary salt. Potassium is predominantly contained within cells and thus the assessment of its regulation requires special emphasis on measurement of steady-state body stores and potassium distribution across cell membranes. However, the methods used to make all of these measurements require assumptions that may not hold in the altered state of uremia. This raises problems in interpretation requiring critical analysis before conclusions can be made regarding sodium and potassium homeostasis in patients with chronic renal failure. This review focuses on abnormalities of body fluids, sodium and potassium in patients with creatinine clearances of less than 20 ml/min due to chronic renal failure and the impact of conservative therapy, dialysis and renal transplantation on these patients.

Renal handling of potassium in dogs with chronic renal insufficiency

The dynamics of potassium excretion were examined in normal dogs and dogs with chronic renal insufficiency of at least 4 weeks' duration (remnant model). All animals, in balance on diets providing 15, 50, or 100 mEq of potassium and 100 mEq of sodium, were challenged with 50 mEq of potassium chloride. Immediately thereafter, hourly clearances were obtained for 5 hours. Irrespective of dietary potassium, mean fasting serum potassium and urinary potassium excretion (UKV) were similar in normal and remnant dogs with mean GFR's of 57 +/- 3 and 16 +/- 3 ml/min, respectively. After orogastric administration of 50 mEq potassium, serum potassium rose significantly more in remnant (2.2 to 2.5 mEq/liter) than in normal (0.9 to 1.2 mEq/liter) groups (P less than 0.001). Conversely, UKV increased significantly less, 70 to 96 vs. 151 to 194 micro Eq/min, respectively (P less than 0.001). In 5 hours, normal animals excreted 61 to 67% of the load, but remnant dogs only 30 to 37% (P less than 0.001). In all groups, UKV correlated directly with serum potassium concentration. But this relationship was markedly attenuated in the remnant groups (P less than 0.001) and independent of dietary potassium. In contrast, the same slope describes the relationship between UKV/GRF and serum potassium for all, normal and remnant, animals. The blunted kaliuresis occurred despite the more severe hyperkalemia in remnant than in normal dogs; it was not associated with significant changes in acid-base, diuresis, natriuresis, serum glucose, insulin, and glucagon concentrations and occurred despite prolonged hyperaldosteronism. The results demonstrate a severe limitation of the remnant kidney's ability to rapidly excrete a potassium load. Changes in serum potassium, or a consequence thereof, are important for the urinary excretion of potassium following its acute administration.

Epinephrine and potassium homeostasis

The effect of epinephrine on potassium metabolism was examined in six subjects. Each subject participated in four studies as follows: (1) potassium chloride infusion (0.75 mEq/kg, i.v.) given over 2 hours, (2) epinephrine (0.05 micrograms/kg.min) plus potassium chloride, (3) propranolol (1.43 micrograms/kg.min) plus epinephrine plus potassium chloride, and (4) propranolol plus potassium chloride. The epinephrine infusion with potassium chloride led to a marked improvement in potassium tolerance, which was due to a greater than twofold increase in the extrarenal disposal of potassium (P less than 0.001). The enhancing effect of epinephrine on extrarenal potassium uptake was completely reversed with the beta-blocking agent propranolol. When propranolol alone was infused with potassium chloride, a significant decrease in the extrarenal disposal of potassium was observed. When potassium chloride was infused alone, 47% of the administered potassium load was excreted in the urine. Epinephrine infusion with potassium chloride markedly inhibited the urinary excretion of potassium (UkV) to rates that were actually below the basal potassium excretion rate (P less than 0.001). Propranolol almost completely reversed this effect of epinephrine on UkV, and when propranolol was infused alone, an enhancement in UkV (P less than 0.005) was observed. Insulin adds only a minor contribution to the enhancing effect of epinephrine on extrarenal potassium disposal and dose not contribute at all to the inhibitory effect of epinephrine on renal potassium excretion. These results demonstrate that epinephrine ameliorates the rise in plasma potassium concentration following potassium chloride infusion. Because none of the infused potassium was excreted during the 4-hour study period, the improvement in potassium tolerance must result from an enhancement in extrarenal potassium disposal. The ability of propranolol to reverse both the extrarenal and renal effects indicates that the action of epinephrine is mediated via stimulation of the beta receptor.

Increased thirst and plasma arginine vasopressin levels during 2-deoxy-D-glucose-induced glucoprivation in humans

Insulin-induced hypoglycemia by unknown mechanism(s) increases plasma arginine vasopressin (AVP) levels in humans. Mechanisms for increased AVP levels during central nervous system glucoprivation were investigated by administering 20-min i.v. infusions of 2-deoxy-d-glucose (50 mg/kg), a competitive inhibitor of glucose utilization, or normal saline (sham), to 24 normal volunteers. Some of the infusions were administered in combination with neuropharmacological blocking agents (placebo). The behavioral, physiological, metabolic, and hormonal correlates of 2-deoxy-d-glucose (2DG)-induced gluco-privation and AVP secretion were studied in a group (n = 5) pretreated for 1 wk with either mazindol (1 mg per os three times per day), a potent norepinephrine and dopamine-reuptake blocker, or placebo. A second group (n = 5) received either propranolol (3 mg/3 min followed by 80 mug/min) or normal saline infusion before and during 2DG administration. With 2DG alone, plasma AVP levels increased from 1.3+/-0.3 pg/ml at base line to a peak of 4.5+/-1.4 pg/ml at 60 min and remained elevated for 150 min. From 30 to 180 min after 2DG administration, the 2DG-infused volunteers increased their water intake in comparison with sham-infused volunteers. Marked increases in epinephrine and slight increases in norepinephrine were associated with increases in plasma glucose and renin activity and decreases in plasma potassium. Plasma sodium and osmolality increased transiently and mean arterial pressure (MAP) fell. These changes, however, were small and inconstant and could not account for the observed increases in thirst and AVP levels. Pretreatment with mazindol prevented the decrease in MAP and the increase in plasma renin activity (PRA) following 2DG infusions without modifying increased thirst, water intake, or AVP responses to glucoprivation. Pretreatment with propranolol effectively blocked beta-adrenoreceptors as evidenced by increased MAP and plasma epinephrine, and abolition of the RPA increases during 2DG-induced glycoprivation, but did not suppress AVP and thirst responses. A cervical cord-sectioned patient lacking descending sympathetic out-flow had a potentiated thirst response to 2DG-induced glucoprivation in the absence of increases in sodium, catecholamines, and PRA. Thus 2DG administration activates mechanisms for increased thirst and AVP which are unrelated to changes in peripheral catecholamines, MAP, PRA, and osmolality.