Elizabeth Welman

The effects of nifedipine on acute experimental myocardial ischemia and infarction in dogs.

We studied 25 anesthetized and thoracotamized dogs before and during 5 hours of acute regional myocardial ischemia. Krypton-81m (81mKr) was infused constantly into the aortic sinuses. The myocardial equilibrium of this tracer was used to image and assess the distribution of regional myocardial perfusion using a gamma camera and digital computer. The epicardial ECG was recorded, S-T segment elevation and the loss of R and appearance of Q waves were measured, and the plasma activity of creatine kinase (CK) was determined in aortic and coronary venous blood throughout these experiments. Ten dogs underwent left anterior descending coronary artery (LAD) narrowing for 5 hours and received no drugs. Five dogs received nifedipine 13 μg/kg, and another five received 1.0 μg/kg intravenously 30 minutes after LAD narrowing. Those dogs receiving nifedipine, 13 μg/kg, showed a 30% fall in aortic pressure, a 12% rise in heart rate, and an extension of regional ischemia. The ECG showed an extension of infarct size, and CK release into the coronary vein appeared earlier than in the controls. Dogs receiving nifedipine, 1 μg/kg, showed a 12% fall in blood pressure, no rise in heart rate, an improvement in regional perfusion, and ECG signs that suggested limitation of infarct size. There also was delayed release of coronary venous CK. The effects of nifedipine on the natural history of regional myocardial perfusion, the electrocardiogram, and enzyme release from the heart were dose related and cannot be generalized. These observations warrant further clinical investigation to improve the use of this agent in man. Circ Res 44: 16-23, 1979

Properties of lysosomes in guinea pig heart: subcellular distribution and in vitro stability.

Abstract Some 20 hydrolytic enzymes, known to be of lysosomal origin in rat liver, were assayed in fractions of guinea pig heart. The enzymes included glycosidases, esterases, proteases (cathepsins) and nucleases. All exhibited structure-linked latency and had optimal activity in acid pH, conforming to the biochemical definition of lysosomal enzymes. Six enzymes which had high activity in guinea pig heart were also measured in rat liver using the fractionation and assay methods employed for myocardium. The acid hydrolase activities of the two tissues are compared and discussed in relation to the cellular origins of the organelles with which they are associated. A lysosome-rich suspension was prepared from guinea pig left ventricle by differential centrifugation. The isolated lysosomes were subjected to various labilizing conditions and the rate of lysosome disruption was monitored by measurements of latent acid hydrolase activity. Loss of latent activity was accelerated by heating, hypotonicity, changes in pH and by addition of NaCl and KCl. The kinetics of lysosomal enzyme release were similar for each of the enzymes tested, with the exception of β-glucuronidase which was released more rapidly by heating and less rapidly by hypotonicity. Subcellular distribution profiles of the acid hydrolases in guinea pig heart were obtained by sucrose density gradient centrifugation. Hearts from both normal and Triton WR 1339 treated animals were fractionated. The modal equilibrium densities of the acid hydrolases revealed the presence of five biochemically distinct lysosomal populations in ventricle tissue, three of which were accessible to Triton WR 1339. The findings in this study show that myocardial lysosomes are a heterogeneous group of organelles with different enzymatic constituents and different physical properties. In view of this there is a need for careful choice of representative marker enzymes in studies on the functions of myocardial lysosomes and their role in disease.

Natural history and evaluation of Q waves during acute myocardial infarction.

Serial 72 point praecordial electrocardiographic maps were recorded in 45 patients with uncomplicated acute anterior myocardial infarction. These were analysed and the serial changes in Q waves and ST segments were recorded. Cardiospecific enzyme release curves were constructed from repeated measurements of the plasma activity of the myocardial isoenzyme of creatine kinase (MB CK) during 4 days after the onset of chest pain. The praecordial maps showed that Q waves appeared in the second hour after the onset of chest pain and the development of this electrocardiographic sign was completed within 12 hours. There were complex relations between the development of Q waves, the natural history of ST segment elevation, and the release of MB CK activity. The praecordial area of ST segment elevation at 2 hours was directly related to the fully developed Q wave area at 24 hours after the onset of chest pain. The electrical activity of affected myocardium was lost before peak plasma MB CK activity.

Electrocardiographic precordial mapping in anterior myocardial infarction. The critical period for interventions as exemplified by methylprednisolone.

Serial 72-point precordial mapping of ECG has been recorded to describe the natural history of changes in the precordial areas of ST segment elevation and the development of Q waves in 51 patients with acute uncomplicated anterior myocardial infarction. Eight patients have been studied in the same way but received 25 mg/kg of methylprednisolone sodium succinate as a single intravenous injection within 6 hours from the onset of chest pain. There was a linear relationship between the stable precordial area of Q waves at 24 hours and the rapidly changing precordial areas of ST segment elevation at 2--3 hours, 5--6 hours and 12 hours after the onset of pain in the untreated patients. When methylprednisolone was given, the treated patients developed a smaller precordial area of Q waves at 24 hours than was predicted from the precordial area of ST elevation recorded before the drug was given. This study has introduced a technique that can provide a qualitative assessment of the relationship between ECG evidence of ischemia and infarction in each patient.

Enhanced lysosome fragility in the anoxic perfused guinea pig heart: Effects of glucose and mannitol☆

Guinea pig hearts were perfused under aerobic and anoxic conditions in the presence and absence of glucose or mannitol. Samples of the coronary perfusate were collected and assayed for creatine phosphokinase (CPK), hydroxybutyrate dehydrogenase (HBDH), leucyl-β-naphthylamidase (LBN) and lysosomal enzyme activities. After various periods of perfusion samples of left ventricle were homogenized and the specific activities (mu/mg protein) of N-acetyl-β-glucosaminidase, N-acetyl-β-galactosaminidase, β-glucuronidase and cathepsin C were determined. Estimates of lysosomal integrity were made from measurements of the latency and sedimentability of the marker enzymes. In control aerobic studies, with or without glucose or mannitol, there was an initial wash-out of CPK, HBDH and LBN with no further enzyme release for up to 6 h. The specific activities and the latency and sedimentability values of the lysosomal enzymes in cardiac homogenates were generally unaffected by aerobic perfusions. In contrast, during anoxic perfusions in the absence of glucose large amounts of CPK, HBDH and LBN were released into the coronary perfusate. The latency and sedimentability of each of the lysosomal enzymes was considerably decreased as a result of anoxic perfusion indicating enhanced lysosome fragility. These changes were significant after 30 min and progressed with the duration of anoxia. The specific activities of the lysosomal enzymes were significantly increased after 6 h anoxic perfusion. Inclusion of glucose in the anoxic perfusion medium did not prevent the release of CPK, HBDH and LBN in the early stages of anoxia but a reduction in myocardial enzyme release was observed in the later stages. The presence of glucose considerably delayed the onset of lysosomal membrane labilization but caused further increases in the specific activities of three of the acid hydrolases. Equimolar concentrations of mannitol had a limited effect on lysosome stability indicating that the protective effect of glucose was mainly due to its metabolic action.

Lysosomal and cytosolic enzyme release in acute myocardial infarction: effects of methylprednisolone.

Serial venous blood samples were obtained from 45 patients suffering myocardial infarction. Ten of these patients received 25 mg/kg methylprednisolone sodium succinate intravenously within 4 hours of the onset of chest pain. The activities of creatine kinase (CK) and its MB-isoenzyme were assayed in the plasma. A lysosomal enzyme, N-acetyl-,B-glucosaminidase (NAG) was also assayed. In the control group of patients the peak activity of CK occurred at a mean time of 21.3 ± 1.3 hours after the onset of chest pain, while the peak activities of CK-MB and NAG occurred at 18.1 ± 1.6 hours and 18.0 ± 1.0 hours, respectively. There was an exponential relationship between the peak values of CK and NAG activity and a linear relationship between peak CK-MB and NAG activity. In the patients who received methylprednisolone the peak enzyme activities were delayed until 27.1 hours for CK, 27.0 hours for CK-MB and 27.3 hours for NAG. The mean peak value for NAG activity was considerably lower in the treated patients, and there was no relationship between the activities of the lysosomal enzyme and either CK or CK-MB. These findings are consistent with previous experimental results which suggest that methylprednisolone can delay tissue damage and stabilize lysosomal membranes during acute myocardial ischemia

Electron microscopy of lysosomal fractions from guinea pig heart

Abstract Lysosomal fractions of guinea pig heart were prepared by density gradient centrifugation and identified by biochemical measurements of acid hydrolase activity. The particulate material in samples of each fraction was sedimented by high speed centrifugation and fixed by a novel method developed for isolated organelles. Electron microscopy of the fractions showed the presence of two types of osmiphillic organelles which have previously been identified as lysosomes. Granular organelles were found in the low-density lysosomal fraction while membranous organelles were predominant in the three higher density fractions. Treatment with digitonin destroyed these organelles in all fractions and rendered the acid hydrolases unsedimentable.

The interpretation of thallium-201 cardiac scintigrams. Studies in experimental ischemic heart disease in dogs.

Twenty-one anesthetized and thoracotamized dogs were studied. Scintigrams of the heart were recorded using a continuous infusion of krypton-81m into the aortic sinuses as well as intravenous injections of thallium-201. A gamma camera linked to a digital computer was used to record the myocardial distribution of these tracers. The distribution of 2O1T1 was similar to that of 81mKr when myocardial blood flow was normal (seven dogs). In 14 dogs, the left anterior descending coronary artery (LAD) was narrowed to produce a regional decrease in myocardial blood flow. Blood flow changes were measured with an electromagnetic flowprobe. When the epicardial ECG was normal in seven dogs, the 201Tl scintigram showed no regional decreases in activity when the tracer was delivered after LAD narrowing. In contrast, a decrease in the activity of 81mKr was observed in the region supplied by the LAD. When the decrease in blood flow was associated with ECG signs of ischemia in seven dogs, both 8lmKr and 2O1T1 scintigrams showed decreased activity in the ischemic area. The cardiac distribution of 201Tl was determined in five dogs while myocardial blood flow and metabolism were normal. LAD narrowing then produced 24 hours of severe myocardial ischemia. The distribution of creatine kinase activity in the left ventricle (U/mg DNA) was similar to the distribution of 2O1T1 (counts/mg DNA), r = 0.83; P = < 0.001. These studies suggest that 2O1T1 scintigraphy of the heart can demonstrate decreases in regional myocardial perfusion only when metabolism is disturbed.

Loss of respiratory enzyme activity in anoxic myocardium effect of propranolol

Guinea pig hearts were perfused anoxically with and without dl-propranolol hydrochloride (0.1 mg.l−1) to determine whether a therapeutic level of this drug could protect the inner mitochondrial membrane. After 5 h anoxia, the specific activities of the mitochondrial inner membrane enzymes, succinate dehydrogenase and cytochrome oxidase, were reduced to approximately half of the activities before perfusion. The activity of the mainly cytosolic enzyme, creatine kinase, was reduced by 58% during 5 h anoxia. In the presence of propranolol, the loss of mitochondrial enzyme activity was significantly reduced, while the loss of creatine kinase activity was unaltered. These findings indicate (1) that loss of respiratory enzyme activity is a consequence of irreversible cellular damage due to anoxia, (2) that a therapeutic level of propranolol conserves respiratory enzyme activity and (3) that the protective action of this level of propranolol is insufficient to conserve creatine kinase activity.