Plasma potassium and phosphate concentrations--influence by adrenaline infusion, beta-blockade and physical exercise

Effect of blood volume change related to intensity of intradialytic aerobic exercise on hemodialysis adequacy: a pilot study

PURPOSE

Intradialytic exercise may improve dialysis efficiency; however, the association between changes in blood volume (BV) related to exercise intensity and solute removal kinetics remains unknown. We herein investigated the relationship between changes in BV with exercise and removal of solute molecules during hemodialysis.

METHODS

Each of the 21 hemodialysis patients underwent cardiopulmonary exercise test to measure anaerobic threshold (AT). According to the exercise intensity, patients were classified into two groups, the low group (n = 12), whose intensity was below the AT, and the high group (n = 9), whose intensity was at the AT level. Each patient completed two trial arms of resting and discontinuous exercise dialysis sessions in a randomized manner.

RESULTS

The change in BV with the exercise dialysis session in the high group decreased during exercise (p = 0.028) and remained decreased after exercise (p = 0.016), compared with the low group. In the low group, compared with routine sessions, the removal of potassium (p = 0.030), phosphate (p = 0.024), and urea nitrogen (p = 0.065) increased during exercise, but the total removal of these solutes did not change. In the high group, the removal of phosphate (p < 0.001) and urea nitrogen (p = 0.018) after exercise and even total phosphate (p = 0.027) decreased.

CONCLUSION

These findings suggest that the removal of small solute molecules is improved during exercise in intradialytic low-intensity exercise with no change in BV, and decreased after exercise in high-intensity exercise with a decrease in BV.

CLINICAL TRIALS REGISTRY

Trial retrospectively registered at the UMIN Clinical Trials Registry: study number UMIN000038629 (Registration date: September 7, 2019).

Hypophosphatemia compared to classical biomarkers of tonic clonic seizures

BACKGROUND

Hypophosphatemia was recently reported as a potential marker of tonic-clonic (TC) seizures among patients with transitory loss of consciousness (TLOC). Its value compared to classical markers (creatine kinase [CK] and lactate) is however unknown.

AIM

Compare the diagnostic performance of hypophosphatemia, plasma CK, and lactate levels for distinguishing TC seizures from other TLOCs, alone or in combination.

METHODS

128 patients aged 18-90, consecutively admitted to our hospital emergency department for TLOC were included. Diagnostic accuracy of plasma phosphate, CK, and lactate levels were compared with ROC curves.

RESULTS

We found significantly higher CK (median 154 U/l, range 38-5608; vs 115.5, 37-2340 U/l; p = 0.037) and lower phosphatemia (median 0.79 mmol/l, 0.34-1.37; vs 0.93, 0.52-1.89 mmol/l, p = 0.007) in TC seizures compared to other TLOCs; lactatemia was not different, although using a smaller sample (n = 72). Hypophosphatemia was the only independent predictor of TC seizures, even in later samples (>2 h). Comparing ROC curves, Combining hypophosphatemia and hyperCKemia had higher diagnostic accuracy for TC seizures than hyper-CKemia alone (AUC 0.68, 95 % CI 0.571-0.783 vs. 0.59, 95 % CI 0.475-0.706; p = 0.018), but the combination was only marginally better than hypophosphatemia alone (AUC 0.67, 95 % CI 0.559-0.778).

CONCLUSION

Hypophosphatemia seems to be more useful than CK levels for diagnosing TC seizures in patients assessed in an emergency setting for TLOC. Combining both parameters together does not significantly increase the diagnostic yield. No conclusion could be drawn regarding the comparison with lactate. A prospective study is needed.

Loading and skeletal development and maintenance

Mechanical loading is a major regulator of bone mass and geometry. The osteocytes network is considered the main sensor of loads, through the shear stress generated by strain induced fluid flow in the lacuno-canalicular system. Intracellular transduction implies several kinases and phosphorylation of the estrogen receptor. Several extra-cellular mediators, among which NO and prostaglandins are transducing the signal to the effector cells. Disuse results in osteocytes apoptosis and rapid imbalanced bone resorption, leading to severe osteoporosis. Exercising during growth increases peak bone mass, and could be beneficial with regards to osteoporosis later in life, but the gain could be lost if training is abandoned. Exercise programs in adults and seniors have barely significant effects on bone mass and geometry at least at short term. There are few data on a possible additive effect of exercise and drugs in osteoporosis treatment, but disuse could decrease drugs action. Exercise programs proposed for bone health are tedious and compliance is usually low. The most practical advice for patients is to walk a minimum of 30 to 60 minutes per day. Other exercises like swimming or cycling have less effect on bone, but could reduce fracture risk indirectly by maintaining muscle mass and force.

Medication-induced hypophosphatemia: a review

Hypophosphatemia (serum phosphorus concentration <2.5 mg/dl, 0.8 mmol/l), although rare in the general population, is commonly observed in hospitalized patients and may be associated with drug therapy. In fact, hypophosphatemia frequently develops in the course of treatment with drugs used in every-day clinical practice including diuretics and bisphosphonates. Proper diagnostic approach of patients with low serum phosphorus concentrations should involve a detailed medical history with special attention to the recent use of medications. The clinical manifestations of drug-induced hypophosphatemia are usually mild but might also be severe and potentially life-threatening. This review aims at a thorough understanding of the underlying pathophysiological mechanisms and risk factors of drug therapy-related hypophosphatemia thus allowing prevention and effective intervention strategies.

Dynamics and consequences of potassium shifts in skeletal muscle and heart during exercise

Since it became clear that K(+) shifts with exercise are extensive and can cause more than a doubling of the extracellular [K(+)] ([K(+)](s)) as reviewed here, it has been suggested that these shifts may cause fatigue through the effect on muscle excitability and action potentials (AP). The cause of the K(+) shifts is a transient or long-lasting mismatch between outward repolarizing K(+) currents and K(+) influx carried by the Na(+)-K(+) pump. Several factors modify the effect of raised [K(+)](s) during exercise on membrane potential (E(m)) and force production. 1) Membrane conductance to K(+) is variable and controlled by various K(+) channels. Low relative K(+) conductance will reduce the contribution of [K(+)](s) to the E(m). In addition, high Cl(-) conductance may stabilize the E(m) during brief periods of large K(+) shifts. 2) The Na(+)-K(+) pump contributes with a hyperpolarizing current. 3) Cell swelling accompanies muscle contractions especially in fast-twitch muscle, although little in the heart. This will contribute considerably to the lowering of intracellular [K(+)] ([K(+)](c)) and will attenuate the exercise-induced rise of intracellular [Na(+)] ([Na(+)](c)). 4) The rise of [Na(+)](c) is sufficient to activate the Na(+)-K(+) pump to completely compensate increased K(+) release in the heart, yet not in skeletal muscle. In skeletal muscle there is strong evidence for control of pump activity not only through hormones, but through a hitherto unidentified mechanism. 5) Ionic shifts within the skeletal muscle t tubules and in the heart in extracellular clefts may markedly affect excitation-contraction coupling. 6) Age and state of training together with nutritional state modify muscle K(+) content and the abundance of Na(+)-K(+) pumps. We conclude that despite modifying factors coming into play during muscle activity, the K(+) shifts with high-intensity exercise may contribute substantially to fatigue in skeletal muscle, whereas in the heart, except during ischemia, the K(+) balance is controlled much more effectively.

Effect of endurance training on postexercise parathyroid hormone levels in elderly men

The present study was designed to evaluate the effects of 6-wk endurance training on serum parathyroid hormone (PTH) levels and on other parameters at rest and after a maximal exercise test (MET) in 24 55- to 73-yr-old men. Before training, MET was found to induce a significant increase in PTH levels as compared with resting values. This MET-induced rise in PTH was accompanied by enhanced total calcium, phosphate, alkaline phosphatase (ALP), osteocalcin, and albumin levels. After the training period (75-80% maximal heart rate, 1 h.d-1, 4 d.wk-1), the changes induced by MET in calcium, phosphate, ALP, and albumin levels followed the same pattern as before training. Conversely, the MET-induced increase in PTH levels was found markedly more pronounced after training than in untrained conditions (+21.9% vs +11.1%, respectively, P < 0.05). Furthermore, lower values of osteocalcin were found after training as compared with pretraining values, both at rest and after maximal exercise. These findings indicate that 6 wk of endurance training enhanced exercise-related release of PTH and reduced osteocalcin levels in elderly men. This might be of importance regarding bone status in the elderly, as exercise is proposed as a preventive measure against osteopenia.

Effects of increased arterial epinephrine on insulin, glucose and phosphate

The relationship between sympathetic nervous system activity and glucose and insulin metabolism is not fully understood. In the present study we therefore investigated the effect of raising arterial plasma epinephrine within the lower pathophysiological concentration range on insulin, glucose and phosphate in blood. Arterial plasma epinephrine was raised over 60 min by a stepwise increasing intravenous infusion in healthy men aged 20-40 years (n = 40). Compared with infusion of saline, epinephrine caused a small but significant rise in serum insulin of 10 +/- 26 pmol/L (p = 0.016), more than 70% increase in serum glucose (p < 0.0001) and a decrease in serum phosphate (p < 0.0001). The changes in serum insulin during epinephrine infusion correlated negatively with the changes in arterial plasma epinephrine (r = -0.46, p = 0.003) and the changes in serum phosphate correlated negatively with the changes in serum glucose (r = -0.42, p = 0.007). Thus, arterial plasma epinephrine raised within the lower pathophysiological concentration range over a rather short period of time (60 min) has pronounced effects on insulin, glucose and phosphate in blood. These results suggest that epinephrine when infused acutely may suppress the insulin response to raised glucose, and that the acute hypophosphatemic effect of epinephrine is related to the glucose production. Thus, when epinephrine is released into the circulation during various forms of daily stress, e.g. mental stress, it may significantly affect insulin and glucose metabolism.

Review of the literature: severe hyperphosphatemia

A patient with a markedly elevated serum phosphorus level (23.9 mg/dL) is described, followed by a brief review of severe hyperphosphatemia. Elevated serum phosphorus levels may be artifactual or true. True hyperphosphatemia is usefully subdivided according to (a) whether phosphorus is added to the extracellular fluid from a variety of exogenous or endogenous sources, or (b) whether the urinary excretion of phosphorus is reduced from either decreased glomerular filtration or increased tubular reabsorption. Severe hyperphosphatemia, defined herein as levels of 14 mg/dL or higher, is almost invariably multifactorial--usually resulting from addition of phosphorus to the extracellular fluid together with decreased phosphorus excretion. The hyperphosphatemia of the patient described herein appeared to result from a combination of dietary phosphorus supplementation, acute renal failure, acute pancreatitis, and ischemic bowel disease, complicated by lactic acidosis.

Sympathetic nervous system involvement in essential hypertension: increased platelet noradrenaline coincides with decreased beta-adrenoreceptor responsiveness

Platelet catecholamine content may reflect integrated plasma catecholamine concentrations over time. The present study aimed at examining sympathetic nervous system (SNS) involvement in essential hypertension by assessing platelet noradrenaline (NA) and typically beta-adrenoreceptor mediated responses to adrenaline (A) infusion as indices of sympathetic tone. Healthy white men were recruited by public advertising and screening (mean +/- SD): Hypertensives (n = 13, sitting blood pressure [BP] 153 +/- 13/106 +/- 7 mmHg, age 34 +/- 5 years, weight 83 +/- 10 kg) were compared to normotensives (n = 13, sitting BP 114 +/- 9/75 +/- 9 mmHg, age 30 +/- 6 years [n.s.], weight 82 +/- 9 kg [n.s.]). Loss of platelet granular contents (including NA) prior to analysis was minimized by studying young subjects (age range 20-40 years, minimal atherosclerosis), using arterial blood sampling, and processing blood immediately. These procedures resulted in plasma beta-thromboglobulin and platelet factor 4 levels which were not significantly different between groups. Sympathetic activation resulting from stress was minimized by not labelling subjects as either hypertensive or normotensive. Mean arterial platelet NA content was significantly higher in hypertensives (64 +/- 31 pg/mg of platelet weight) compared to normotensives (43 +/- 20 pg/mg, p < 0.05) both at baseline and following 35% expansion of the circulating platelet pool by A infusion (p < 0.05) and correlated with arterial NA in the hypertensives (r = 0.79, p < 0.002) but not in the normotensives (r = 0.04, n.s.). Similar increases in platelet and plasma A during infusion in both groups suggest unchanged platelet uptake capacity and plasma clearance in the hypertensive group.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug- and nutrition-induced hypophosphatemia: mechanisms and relevance in the critically ill

OBJECTIVE

To provide an outline of the drugs and nutritional therapy that could contribute to the development of hypophosphatemia in the critically ill patient.

DATA SOURCES

Computerized abstracting services, references to primary literature articles, and review publications were screened for references to drug- or nutrition-related hypophosphatemia.

STUDY SELECTION

Studies primarily describing responses in adults were selected. Animal research is described that illustrates findings in humans.

DATA EXTRACTION

Information was abstracted from the findings of individual case reports and clinical trials.

DATA SYNTHESIS

Data are organized by mechanism of possible effect on serum phosphate concentration. No reference is made to drugs that do not have an effect on phosphate metabolism.

CONCLUSIONS

Hypophosphatemia can have significant effects that would hinder recovery of the critically ill patient. Antacids, catecholamines, beta-adrenergic agonists, sodium bicarbonate, and acetazolamide are commonly used therapeutic agents that could contribute significantly to the development of hypophosphatemia. Provision of nutrition to the chronically malnourished individual or chronic administration of phosphate-depleted parenteral nutrition could produce symptoms associated with hypophosphatemia. Other drugs could have a mild effect on lowering serum phosphate concentrations, but would be unlikely to produce symptoms unless combined with other etiologies of hypophosphatemia.

On the relationships between mineral metabolism, obesity and fat distribution

Alterations in calcium metabolism have been associated with cardiovascular risk factors. An altered binding of calcium to plasma proteins and raised levels of parathyroid hormone (PTH) have been described in morbid obesity. In the present study, indices of mineral metabolism were related to obesity (body mass index, BMI) and fat distribution (waist to hip ratio, w/h) in 194 subjects with a wide range of BMI and w/h. The ratio of total serum calcium to plasma ionized calcium (Ca2+) was found to be significantly correlated to both BMI (r = 0.20, P < 0.02) and w/h (r = 0.22, P < 0.005). Serum phosphate was also correlated to both of the indices of obesity in an inverse way (r = -0.24, P < 0.0008 for BMI and r = -0.33, P < 0.0001 for w/h). These relationships were still significant when the influences of age, sex and serum creatinine were included in the multiple regression analysis. This kind of analysis also disclosed that w/h was superior to BMI as a determinant of serum phosphate and the total calcium/Ca2+ ratio in serum. PTH was not significantly correlated to any of the indices of obesity. In conclusion, fat distribution rather than obesity per se was found to be associated with an altered mineral metabolism.

The effects of exercise on serum potassium levels

In view of the significant influence of potassium on the heart, a decision was made to study the effect of exercise on this important ion in two exercise groups of different intensity. The first group consisted of 44 individuals with known coronary artery disease participating in a supervised cardiac rehabilitation program while the other consisted of 30 healthy joggers. Postexercise mean potassium levels were higher in both groups than resting baseline values. In addition, 5 of 44 participants in the coronary artery disease group experienced major potassium increases of 0.9 mmol/L or more while 7 of 30 healthy joggers experienced this magnitude of increase. Remaining unanswered is the question of whether such abrupt rises in potassium levels in this subset of patients alter their vulnerability to cardiac rhythm and conduction disturbances. A question is also raised as to whether rapid return of potassium levels to baseline postexercise contributes to any risks.

Effect of acid-base management with or without carbon dioxide on plasma phosphate concentration during and after hypothermic cardiopulmonary bypass

Variations of the phosphate concentration in plasma were studied in two groups of 12 patients undergoing cardiac surgery with hypothermic cardiopulmonary bypass (CPB). Management of the acid-base status differed between the groups, according to whether or not carbon dioxide was added to the anesthetic gas mixture during hypothermia ('pH-stat' vs. 'alpha-stat' mode) following correction vs. no correction of pCO2 and pH for body temperature. Phosphate variations throughout the study were mostly within normal limits. From the start to the end of CPB, the mean rise in phosphate levels was 70% in the pH-stat group and 37% in the alpha-stat group (p < 0.001). During 3 hours after CPB, the phosphate values continued to rise by a mean of 25% in the alpha-stat patients, but fell by a mean of 3% in the pH-stat patients (p < 0.001). Such different phosphate patterns during and immediately after CPB may reflect profound metabolic disturbances and may be related to the altering effects of CO2 addition and respiratory acidosis on intracellular metabolic activity and phosphate homeostasis.

Potassium and blood pressure

The relationships between serum potassium and urinary excretion of potassium and blood pressure were determined in an unmedicated adult population with a wide range of blood pressure (mean arterial blood pressure 100-130 mm Hg, n = 71). Inverse correlations between both serum potassium concentration and urinary excretion of potassium and standing (but not supine) mean blood pressure were seen (r = -0.41, p less than 0.005 and r = -0.33, p less than 0.01 respectively). These relationships persisted also when the influences of age, sex, obesity and kidney function were taken into account in a multiple regression analysis. The present observation is in accordance with previous reports of an association between potassium metabolism and blood pressure.

Effects of exercise testing, training and beta blockade on serum potassium in normal subjects

To evaluate the effects of exercise testing, training and beta blockade on serum potassium, 40 normal subjects (24 men, 16 women, mean age 33 years) had 4 maximal exercise tests with venipuncture for serum potassium before and less than or equal to 40 seconds after each test. After initial exercise testing, they were randomized to atenolol 50 mg daily, atenolol 100 mg daily, propranolol 80 mg twice daily or placebo. All began a 9-week dynamic exercise program for 8 weeks followed by a 1-week drug-free washout period. Tests were done after weeks 1, 8 and 9. A significant mean increase (p less than 0.05) in serum potassium occurred with maximal exercise in the atenolol 50 mg and propranolol groups after 1 week of treatment (mean +/- standard deviation, 4.78 +/- 0.29 to 5.09 +/- 0.43 mEq/liter and 4.81 +/- 0.55 to 5.30 +/- 0.33 mEq/liter). By week 8 after training, all beta blockade groups showed an increase in postmaximal exercise test serum potassium (atenolol 50 mg, 4.78 +/- 0.29 to 5.11 +/- 0.26 mEq/liter; atenolol 100 mg, 4.95 +/- 0.41 to 5.16 +/- 0.36 mEq/liter; propranolol, 4.81 +/- 0.55 to 5.05 +/- 0.29 mEq/liter). After washout, only the placebo group showed an increase in postmaximal test serum potassium (4.99 +/- 0.46 to 5.35 +/- 0.27 mEq/liter). Data indicate that hyperkalemia with maximal exercise testing increases after training with atenolol and propranolol compared to placebo and that this effect resolves once treatment is discontinued.

Platelet and plasma catecholamines in relation to plasma minerals and parathyroid hormone following acute myocardial infarction

Epinephrine has been shown to lower the plasma concentrations of several minerals and elevate those of parathyroid hormone (PTH). In order to evaluate the possible clinical importance of such experimental observations, 34 patients with acute myocardial infarction (AMI) were studied with daily determinations of plasma catecholamines, minerals, and PTH during the first week after AMI and at follow-up one month later. In addition, platelet catecholamines were determined as they fluctuate more slowly than plasma catecholamines. After infarction initial platelet epinephrine and norepinephrine levels were higher (p less than 0.05 for both) in nonsurvivors than survivors during a one year follow-up. Results suggested that activation of the sympathoadrenal system influences calcium homeostasis following AMI, but that the impact of sympathoadrenal activation on mineral metabolism is of minor clinical significance in the average AMI patient. High platelet catecholamine levels may predict a poor outcome after AMI.

Metabolic, electrocardiographic, and hemodynamic responses to increased circulating adrenaline: effects of selective and nonselective beta adrenoceptor blockade

Twelve healthy male volunteers were given adrenaline infusions, 0.05 microgram/kg body weight/minute over one hundred twenty minutes (min), in order to achieve serum adrenaline concentrations comparable with those seen in acute myocardial infarction. The infusions were given on three occasions, at intervals of at least four weeks. Before the infusions the subjects were given, in random order, two days' pretreatment with placebo, a beta-1-selective adrenoceptor blocker (atenolol), or a nonselective beta blocker (propranolol) with each subject receiving each pretreatment. Six of the volunteers also had a fourth adrenaline infusion, after two days' pretreatment with a beta-2-selective beta blocker, ICI 118551. Adrenaline increased heart rate by 11 beats/min, increased systolic blood pressure by 10 mmHg, and decreased diastolic blood pressure by 15 mmHg. These changes were partly prevented by atenolol. Propranolol and ICI 118551 partly prevented the rise in systolic blood pressure but differed from atenolol in their effects on heart rate and diastolic blood pressure, causing falls in heart rate by 7 beats/min and 12 beats/min respectively, secondary perhaps to increases in diastolic blood pressure by 13 mmHg and 17 mmHg respectively. Adrenaline caused a prolongation of QTc duration by 0.03 second and a flattening of the T-wave amplitude by 1.04 mm. These changes in cardiac repolarization were partly inhibited by atenolol, but the effects of propranolol and ICI 118551 were greater, each causing a reduction of QTc and an increase in T-wave amplitude. During adrenaline infusion S-potassium declined by 0.60 mmol/L, S-magnesium by 0.05, S-calcium by 0.10, and S-phosphate by 0.24, but S-free fatty acids increased nearly threefold. All these changes were statistically significant and were presumably mediated mainly by the beta-2-adrenoceptor, for they were blocked more effectively by the beta-2-adrenoceptor blockers than by the selective beta-1-adrenoceptor blocker. B-glucose increased by 4.1 mmol/L, the increase being practically unaffected by the different pretreatments. These adrenaline-induced hemodynamic, electrocardiographic, and metabolic changes may predispose to arrhythmias and impair cardiac performance after a myocardial infarction. Nonselective beta blockers may be more effective in blocking the electrocardiographic and metabolic effects, but beta-1-selective beta blockers may have hemodynamic advantages.

Serum and urinary phosphate during and after prolonged muscular ischaemia in non-exercising men and women

Serum inorganic phosphate (Pi) concentrations and urinary Pi excretions were measured in nine patients undergoing abdominal aortic bypass grafting (group I) and in nine patients undergoing lower limb arterial embolectomy (group II). In group I, serum Pi concentrations were normal until 24 h after reperfusion, when they decreased, reaching their nadir at 48 h (median Pi 0.45 mmol 1(-1). The urinary phosphate clearance relative to the creatinine clearance (Cp/Cc) increased 5 min after reperfusion reaching a maximal median value (0.454) in the 2-24-h collection period. In group II, eight patients had a normal and one had a subnormal serum Pi before reperfusion. None developed hypo- or hyperphosphataemia and the Cp/Cc remained unchanged. Daily urinary Pi excretion was higher in group I than in group II (P less than 0.03). The authors concluded that the regional muscular ischaemia in non-exercising men and women was not associated with hyperphosphataemia. The possible influence of major surgery and anaesthesia on phosphate homeostasis should be considered.

Exercise stress-induced changes in systemic arterial potassium in angina pectoris

Large fluctuations in systemic arterial potassium have been found during and after exercise in normal subjects. To determine whether similar changes occur in patients with angina pectoris, arterial potassium levels were measured before, during and immediately after maximal bicycle exercise in 20 patients with exertional angina. In 10 of these patients, leg blood flow and arteriovenous potassium levels also were measured. During exercise, arterial potassium increased significantly both from rest to submaximal exercise (4.3 +/- 0.1 to 4.7 +/- 0.1 mmol/liter, p less than 0.01) and from submaximal to maximal exercise (5.4 +/- 0.1 mmol/liter, p less than 0.01). Within 1 minute of cessation of exercise, arterial potassium had decreased to 4.7 +/- 0.1 mmol/liter (p less than 0.001) and continued to decrease to a minimum of 4.1 +/- 0.1 mmol/liter between 3 and 5 minutes after exercise, significantly less than the rest value (p less than 0.05). At maximal exercise (99 +/- 9 watts), the calculated release of potassium from each leg reached 2.7 +/- 1.3 mmol/min. Four minutes after exercise, the leg muscles were resorbing potassium at 0.24 mmol/min. In these patients with exertional myocardial ischemia, the magnitude and rapidity of arterial potassium changes during and after exercise resemble those found in normal subjects, but occurred at much lower workloads. Release and resorption of potassium by exercising muscle in patients with angina pectoris may cause potentially arrhythmogenic arterial potassium fluctuations.

Effects of propranolol and verapamil on plasma ionized calcium and parathyroid hormone in short-term intense isokinetic leg exercise

Physical exercise, beta-adrenergic stimulation and calcium channel blockade can affect calcium homeostasis. The present study investigated, in eight healthy males, the effects of orally administered propranolol or verapamil during a 2-min maximal, isokinetic, leg exercise. Immediately after exercise the plasma ionized calcium concentrations were increased, in control and drug tests, by 5-6%, and within 5 min of recovery they were almost returned to baseline. Serum parathyroid hormone (PTH) concentrations were unchanged at termination of exercise, but they increased during the first 5 min of recovery, coincident with the decline in calcium concentrations, which, however, were still elevated. Neither verapamil nor propranolol selectively changed basal or exercise plasma ionized calcium or serum PTH concentrations. Muscle strength, blood pH, lactate concentrations and plasma volume changes were not affected by any drug. Verapamil did not have any specific effect on the concentrations of plasma magnesium, phosphate, potassium or sodium while propranolol increased the concentrations of plasma potassium and decreased those of phosphate during exercise as well as recovery.