Serum phosphate shift in acute myocardial infarction

Serum phosphate increase during short-term beta-adrenoceptor blockade in thyrotoxicosis

We studied the changes in blood plasma electrolytes during acute and short-term treatment with four different beta-adrenergic-blocking agents in 31 patients with hyperthyroidism. Serum phosphate increased during the first four hours and remained elevated after one week both after cardioselective (acebutolol) and non-cardioselective (oxprenolol, pindolol and timolol) beta-blockade (p less than 0.05). Albumin decreased after four hours but no change was found after one week. Serum creatinine increased after one week in the acebutolol-treated group, while sodium, potassium and albumin-corrected calcium in serum did not change. The hyperphosphatemic effect may be due to blockade of beta 1-adrenoceptors, since the effect of the cardioselective acebutolol was no less than that of the non-cardioselective beta-adrenoceptor blockers.

Metabolic, hemodynamic, and electrocardiographic responses to increased circulating adrenaline: effects of pretreatment with class 1 antiarrhythmics

In order to study the effects of treatment with class 1 antiarrhythmics on the metabolic, hemodynamic, and electrocardiographic responses to adrenaline, 12 healthy volunteers were infused on four occasions, after pretreatment with placebo, disopyramide, mexiletine, and flecainide, respectively, with adrenaline at a rate producing serum adrenaline concentrations comparable with those seen in acute myocardial infarction. After pretreatment with placebo adrenaline caused significant falls in serum potassium, serum magnesium, serum calcium, and serum phosphate and a significant increase in blood glucose. Adrenaline also caused a significant increase in heart rate and systolic blood pressure and a significant fall in diastolic blood pressure. On the electrocardiogram a significant prolongation of QTc duration and a flattening of the T-wave amplitude were seen. Pretreatment with disopyramide had no effect on the hemodynamic response to adrenaline but caused a significant prolongation of Qtc duration before the adrenaline infusion. Pretreatment with mexiletine was associated with a significantly greater fall in serum potassium during adrenaline infusion, and pretreatment with flecainide with a greater fall in serum magnesium, as compared with placebo pretreatment Flecainide also caused a significant prolongation of the QRS duration before adrenalin infusion, and after all the active pretreatments a prolongation of QRS duration was seen during adrenaline infusion. The metabolic and hemodynamic changes during adrenaline infusion may not only reduce the antiarrhythmic efficacy of antiarrhythmics but may also increase the risk of proarrhythmic effects in a clinical setting. These results may help to explain why treatment with antiarrhythmics seems to be without beneficial effect on mortality in post-myocardial infarction patients.

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.

Effects of prolonged adrenaline infusion and of mental stress on plasma minerals and parathyroid hormone

The role of the sympatho-adrenal system for the secretion of PTH in humans is not established. Previous studies on the effects of adrenaline on plasma mineral homeostasis have focused on injections or short-term infusions of adrenaline, and conflicting results concerning calcium and parathyroid hormone (PTH) responses have been reported. We therefore infused adrenaline or placebo continuously for 3 h to 10 healthy volunteers and studied several plasma minerals, as well as PTH levels. Venous plasma adrenaline concentrations increased to the upper physiological range (5 nmol l-1) during adrenaline infusion. Another nine volunteers were exposed for 25 min to mental stress (a colour word conflict test; CWT), which causes marked circulatory changes and raises plasma catecholamine concentrations. Plasma ionized and total calcium, and magnesium concentrations were slowly and gradually reduced during infusion of adrenaline, but there was only a small increase in PTH. Plasma potassium was decreased by adrenaline within 30 min and thereafter did not change further during infusion. There was a marked but transient increase in the plasma free fatty acids concentration, which were not related to the reduction of the calcium or magnesium levels. The adrenaline-induced decrements in calcium, magnesium and potassium, and increases in heart rates persisted 30 min after the infusion, despite a rapid decrease in plasma adrenaline concentrations within 5 min of termination of the infusion. Plasma phosphate concentrations were lowered during the first 90 min of adrenaline infusion, but after 3 h they had returned to baseline despite continued infusion. CWT induced small increments of the plasma ionized calcium and PTH concentrations. Plasma potassium levels were raised despite increases in plasma adrenaline at the beginning of the stress test, while phosphate values were reduced at the end of the test. Thus, long-lasting elevations of circulating adrenaline lower plasma ionized and total calcium, phosphate, magnesium and potassium, but the time courses for these changes differed markedly. Despite the reduction of plasma ionized calcium there was only little increase in PTH and thus no indication that sustained elevations of circulating adrenaline stimulates the secretion of PTH in vivo in humans. Responses to acute mental stress and adrenaline infusion differed qualitatively, indicating that adrenaline responses to stress are of minor importance in this respect.