The kinetics of efflux of 5,5-dimethyl-2,4-oxazolidinedione (DMO) from the myocardium

1. The efflux of 14C-labelled 5,5-dimethyl-2,4-oxazolidinedione (DMO) from the myocardium of the rabbit has been studied. The perfusate pH was 7-38. 2. The effluent curve is complex and appears to be the resultant of movement between at least four compartments. 3. The first two probably represent intravascular and extracellular compartments; the last two have smaller rate constants and may represent intracellular spaces. Intracellular pH (pHi) calculated from the effluent curve was 7-23 +/- 0-05. pHi estimated from the steady-state distribution volume of DMO was 7-28 +/- 0-02. The existence of two intracellular compartments suggests that DMO is not homogeneously distrubted in the myocardium. It is suggested that the apparent greater buffering capacity of cardiac than skeletal muscle can be explained by the greater number and volume of mitochondria in the myocardium, compartmentalization of DMO and assumptions inherent in the DMO method for the measurement of pHi.

Paradoxical embolism complicating massive pulmonary embolus

Paradoxical embolism is an unusual but well recognized complication of venous thromboembolic disease. This case report of a patient with massive pulmonary embolism, who had a paradoxical embolus through a patent foramen ovale, emphasizes that in these circumstances surgical intervention is indicated.

Angiosarcoma of pericardium. Problems in diagnosis and management

The clinical histories of two patients with angiosarcoma of the pericardium are described. Both were previously well young men who presented with cardiac tamponade caused by haemorrhagic pericardial effusions. If a pericardiectomy is undertaken for diagnosis, wide excision of the pericardium is recommended. This will provide a large specimen for histological examination and may prevent subsequent development of constriction.

Logical approach to lignocaine therapy

Plasma lignocaine concentrations were measured during and after lignocaine infusions administered for suppressing ventricular dysrhythmias. Twenty-four patients with a primary diagnosis of acute myocardial infarction without gross circulatory disturbance received, after a bolus of lignocaine, either 4 mg/min for 30 minutes, 2 mg/min for two hours, then 1 mg/min thereafter or 1 mg/min throughout. The higher dose regimen produced continous therapeutic levels of lignocaine, which were achieved only after four hours by the lower dose. On the other hand, in patients who had undergone cardiac surgery and who had circulatory and heptic dysfunction the lower dose regimen achieved therapeutic levels early. The plasma half life was longer in the surgical group (P less than 0.02). The higher initial infusion rate is recommended for patients with acute myocardial infarction without gross circulatory impairment.

Is early decline of cardiac function in ischaemia due to carbon-dioxide retention?

There is no satisfactory explanation for the early and rapid decline of cardiac muscle function in ischaemia. Reduction of the energy source for contraction, A.T.P., is insufficient in magnitude and too slow in onset to be the prime cause. It is proposed that a large part of the loss of function is directly attributable to an immediate fall of intracellular pH and results from the accumulation of carbon dioxide and lactic acid; the intracellular acidosis reduces myocardial function by inhibition of that part of the calcium-ion influx associated with contraction.

ECS, intracellular pH, and electrolytes of cardiac and skeletal muscle

The extracellular space (ECS) of muscle from each ventricle of the heart (RV and LV), the atria, diaphragm, and quadriceps was estimated in the anesthetized rabbit from the distribution volumes of [14C]insulin, [14C]sucrose, [51Cr]EDTA, and C1--. Whole-tissue electrolytes were measured and intracellular electrolytes calculated. The ECS of the tissues varied, increasing in the order quadriceps less than LV less than RV less than atria. The volume of distribution of [14C]inulin was always less than that of either [14C]sucrose or [51Cr]EDTA which agreed closely, whereas that of C1-- was always greater. There was no difference in intracellular K+ in muscle from each of the cardiac chambers, whereas intracellular Na+ and C1-- varied, increasing in the order quadriceps less than LV less than RV less than atria. Intracellular pH, measured with [14C]DMO did not differ in any of the tissues studied. It is concluded that, in vivo, the estimated ECS incardiac muscle is lower than that reported in vitro, that [51Cr]EDTA is a satisfactory ECS marker, and that differences in intracellular Na+ and C1-- but not K+ or pH exist between muscle from the cardiac chambers.

Intracellular pH and K+ of cardiac and skeletal muscle in acidosis and alkalosis

The effects of a metabolic and respiratory acidosis and alkalosis on intracellular pH (pHi) and K+ have been compared in cardiac and skeletal muscle from the anesthetized rabbit. The extracellular space and pHi were calculated from the distribution volumes of [51Cr] EDTA and [14C]DMO, respectively. When pHe was varied by altering PCO2, the slope of the line relating pHi to the extracellular pH (pHe) was greater (P less than 0.05--0.001) than that obtained during metabolic changes of pHe in right and left ventricles, atria, diaphragm, and quadriceps. During metabolic acidosis and alkalosis, the slope of pHi/pHe line did not vary between tissues. During respiratory acidosis, there was no difference in slope between cardiac tissues, but it was less in left ventricle than quadriceps (P less than 0.001). In left ventricle intracellular K+ increased in a metabolic (P less than 0.05) or respiratory acidosis (P less than 0.02), whereas in diaphragm it decreased (P less than 0.02). Intracellular K+ correlated with pHe and pHE-PHi. Changes in pHi but not intracellular K+ could explain known differences in myocardial function in respiratory and metabolic acidosis.

Effect of pH on ionic exchange and function in rat and rabbit myocardium

The effects of pH variation on ionic exchange and mechanical function were studied in the arterially perfused rat and rabbit septa. The pH and PCO2 of the control perfusate were 7.40 and 39 mmHg, respectively. In the rabbit septum a metabolic acidosis (pH equals 6.82, PCO2 equals 39 mmHg) caused a loss of 16% of control tension in 12 min. Na+ and K+ exchange were unaltered. A comparable respiratory acidosis (pH equals 6.81, PCO2 equals 159 mmHg) caused a 51% loss of tension in 2 min. Na+ exchange was unaltered but K+ efflux fell from 8.9 +/- 0.6 (mean +/- SE) to 4.9 +/- 0.3 mmol/kg dry wt per min (P less than 0.001, n equals 10). A net gain of K+ of 16.9 +/- 1.7 (n equals 14) mmol/kg dry wt occurred and was attributable to a delayed fall in K+ influx relative to efflux over 15 min. The net gain could not be mimicked by epinephrine administration or blocked by propranolol and was absent in the beating rat septum and the quiescent rabbit septum. These results suggest that the net uptake of K+, which appears to be dependent on a period of depolarization, and the changes of contractility are controlled by the H+ ion concentration at a cellular site whose exchange with the extracellular space is characterized by a considerable restriction of diffusion. Changes of contractility are not related to the net uptake of K+.

Glycoside inotropy in the absence of an increase in potassium efflux in the rabbit heart

The inotropic effect of 1.25 times 10(-6)M acetylstrophanthidin (ACS) and the influx and efflux of labeled potassium (42K+) were studied in the arterially perfused rabbit interventricular septum under control conditions and during respiratory acidosis. An increase in the CO2 content of the gas mixture with which the modified Ringer's solution was equilibrated from 5 to 30% reduced the perfusate pH from 7.37 to 6.66. The increment in developed tension in the presence of ACS was 3.0 +/- 0.2 g (n equals 10) under control conditions, but it was greater, 7.1 +/- 0.9 g (N equals 9) during acidosis (P less than less than 0.001). The net K+ loss due to an increase in K+ efflux was 1.8 +/- 0.2 mmoles/kg wet weight in control experiments but only 0.1 +/- 0.1 mmoles/kg net weight under acidotic conitions (P less than less than 0.001); in seven of nine experiments in respiratory acidosis, no increase in K+ efflux occurred despite a marked positive inotropy. In three septums, K+ influx was reduced by ACS during respiratory acidosis. These results demonstrate that during acidosis ACS inhibits sodium-potassium adenosinetriphosphatase (Na+-K+ ATPase) and causes an inotropic effect but does not increase K+ efflux. K+ efflux cannot be linked to calcium (Ca2+) influx or regarded as the controlling factor of glycoside-induced inotropy. The results give further support to the proposal that digitalis-induced inotropy is secondary to an enhancement of a Na+-Ca2+ exchange system.

A comparison of the ventilatory response to carbon dioxide by steady-state and rebreathing methods during metabolic acidosis and alkalosis

1. The rebreathing and steady-state methods for assessing the response to inhaled carbon dioxide were compared in six normal subjects under control conditions and during metabolic acidosis and alkalosis.

2. The slopes of the CO2 response lines obtained with the two methods under control conditions were not significantly different.

3. Metabolic acidosis and alkalosis produced a significant change in the intercept of the response line when this was assessed with the steady-state technique. The slope of the response lines did not change significantly in alkalosis but there was probably a small increase during acidosis.

4. Using the rebreathing technique there was no significant change in intercept in acidosis and alkalosis, but the slope varied significantly from control values.

5. It is concluded that the two methods of assessing the respiratory response to inhaled CO2 are comparable under normal acid-base conditions. This similarity does not hold in metabolic changes of the acid-base state.

Renal excretion of bicarbonate and hydrogen ions: effects of mannitol diuresis in normal man

1. The pattern of urinary acid excretion during mannitol diuresis was studied in five normal adult subjects.

2. At peak diuresis (osmolal clearance 19·3–27·9 ml/min), the urinary pH approached 6·9 irrespective of the initial pH.

3. Total hydrogen ion excretion fell sharply during mannitol diuresis. Changes in the excretion of ammonium and titratable acid were small and variable, but in each subject bicarbonate excretion increased markedly.

4. Despite previous conflicting published results urinary acid excretion during mannitol diuresis in man resembles that in the dog and is dominated by a bicarbonate diuresis.