Paul J. Laraia

Adenosine 3', 5'-Monophosphate-Dependent Membrane Phosphorylation: A Possible Mechanism for the Control of Microsomal Calcium Transport in Heart Muscle

The role of cyclic adenosine 3′, 5′-monophosphate (AMP) in the control of microsomal calcium ion (Ca2+) transport was studied in microsomes prepared from rabbit heart. These cardiac microsomes contained intrinsic cyclic AMP-dependent protein kinase activity that phosphorylated serine residues in a microsomal protein component with a molecular weight of about 20,000 (determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Intrinsic phosphoprotein phosphatase activity of the microsomal membranes resulted in rapid dephosphorylation of these residues. Microsomes phosphorylated in the presence of 1 × 10−6M cyclic AMP exhibited enhanced Ca2+ uptake. We conclude that reversible phosphorylation of microsomal membranes may be an important mechanism for regulation of microsomal Ca2+ transport by cyclic AMP.

Prognostic value of predischarge low-level exercise thallium testing after thrombolytic treatment of acute myocardial infarction☆

Low-level exercise thallium testing is useful in identifying the high-risk patient after acute myocardial infarction (AMI). To determine whether this use also applies to patients after thrombolytic treatment of AMI, 64 patients who underwent early thrombolytic therapy for AMI and 107 patients without acute intervention were evaluated. The ability of both the electrocardiogram and thallium tests to predict future events was compared in both groups. After a mean follow-up of 374 days, there were 25 and 32% of cardiac events in the 2 groups, respectively, with versus without acute intervention. These included death, another AMI, coronary artery bypass grafting or angioplasty with 75% of the events occurring in the 3 months after the first infarction. The only significant predictors of outcome were left ventricular cavity dilatation in the intervention group and ST-segment depression and increased lung uptake in the nonintervention group. The sensitivity of exercise thallium was 55% in the intervention group and 81% in the nonintervention group (p less than 0.05). Therefore, in patients having thrombolytic therapy for AMI, nearly half the events after discharge are not predicted by predischarge low-level exercise thallium testing. The relatively weak correlation of outcome with unmasking ischemia in the laboratory before discharge may be due to an unstable coronary lesion or rapid progression of disease after the test. Tests considered useful for prognostication after AMI may not necessarily have a similar value if there has been an acute intervention, such as thrombolytic therapy.

Variables associated with a poor prognosis in patients with an ischemic thallium-201 exercise test

To determine the exercise workload, ECG, and thallium-201 image parameters that are most closely associated with a poor prognosis from ischemic heart disease, the test results of 268 patients were reviewed. Only patients with unequivocal thallium-201 redistribution were selected. A multivariate analysis was performed to find the variables that were most strongly associated with the outcomes of coronary revascularization, myocardial infarction, and cardiac death during a follow-up period of 25 +/- 19 months. Patients who underwent early elective revascularization had poorer exercise tolerance and more thallium image abnormalities than those with no events. In the remaining patients myocardial infarction was most closely related to the extent and severity of thallium ischemia (p = 0.0086), whereas cardiac death was associated with abnormal thallium lung uptake (p = 0.0082) and an inability to exercise to 9.6 MET (p = 0.0144). Thus unlike myocardial infarction, cardiac death is best predicted by variables that reflect poor left ventricular function rather than those that indicate ischemia.

Cyclic adenosine 3',5'-monophosphate in human lung.

Abstract Cyclic[ 14 C]adenosine 3′,5′-monophosphate (cyclic AMP) in human lung fragments has been measured by an isotopic method. It was found that aminophylline transiently increased cyclic[ 14 C]AMP by 100% in doses above 1 mM. β-Adrenergic agents, epinephrine and isoproterenol, increased cyclic [ 14 C]AMP by greater than 1000% through at least 10 min of incubation. Combinations of isoproterenol and aminophylline acted synergistically. Norepinephrine alone increased cyclic[ 14 C]AMP but to a lesser degree than isoproterenol or epinephrine. In the presence of β-adrenergic blockade, norepinephrine and epinephrine decreased cyclic [ 14 C]AMP below control values.

Effects of Glucagon on Myocardial Oxygen Consumption and Coronary Blood Flow in Man and in Dog

The effects of intravenous administration of glucagon (50 &mgr;g/kg) on left coronary blood flow and myocardial oxygen consumption were studied in nine patients during diagnostic cardiac catheterization and in six open-chested anesthetized dogs. Coronary blood flow was measured with the 133Xe washout technic in man, and with an electromagnetic flowmeter placed around the left anterior descending coronary artery in the dogs. In the patients, glucagon produced a 31% increase in coronary blood flow and a 29% increase in myocardial oxygen consumption, with no change in coronary arteriovenous (A-V) O2 difference across the heart. In the dogs glucagon produced a 114% increase in coronary blood flow and a 131% increase in myocardial oxygen consumption, again with no change in coronary A-V O2 difference. Thus glucagon is a secondary coronary vasodilator in both man and dog. The modest chronotropic and inotropic effects of glucagon observed in man were only half as great as those observed in the dog. Part or all of this difference in dose-response relationship between the two species may be related to the different experimental conditions of the study.

Autonomic Control of Cardiac C-AMP

Although catecholamines are known to increase cyclic adenosine 3′5′-monophosphate (C-AMP) in heart muscle, the relations of adrenergic and cholinergic mechanisms to inotropy and myocardial C-AMP levels and adenyl cyclase have not been defined. Accordingly, atrial and ventricular muscle preparations were studied in a myograph with a tension recorder. Adenyl cyclase, phosphodiesterase, and C-AMP were measured by chromatographic and isotopic methods. In atrial preparations, norepinephrine (10−5M) increased tension by 80±10% (mean±SE), adenyl cyclase by 40±10% and C-AMP by 75±12%, while carbamylcholine chloride (10−4M) reduced tension by 65±10%, adenyl cyclase by 30±12% and C-AMP by 50±14%. The effects of carbamylcholine chloride on tension, adenyl cyclase, and C-AMP were blocked by atropine 10−5M. In paced ventricular (papillary) muscles, norepinephrine (10−5M) increased tension by 70±10%, adenyl cyclase by 50±11% and CAMP by 90±17%. In contrast, carbamylcholine chloride (10−5M) reduced tension by only 7±5%, adenyl cyclase by 12±8%, and C-AMP by 10±7%. These results demonstrate parallel changes in tension, adenyl cyclase, and C-AMP in atrium and ventricle. The failure of ventricular muscle to respond to carbamylcholine is mirrored by the adenyl cyclase system and C-AMP. Furthermore, the cholinergically mediated tension and adenyl cyclase changes in atria were specifically blocked by atropine. Thus these results relate the different effects of cholinergic agents on atrium and ventricle to adenyl cyclase and C-AMP, and suggest specific receptor localization in these two types of myocardia.

Hormonal regulation of myocardial adenosine 3′,5′-monophosphate

Abstract A simple, sensitive, and specific method for measuring changes in adenosine 3′,5′-monophosphate (cyclic AMP) has been applied to the investigation of hormonal control of myocardial cyclic AMP in the rat ventricular slice. Catecholamines have been demonstrated to produce a 100% increase in cyclic AMP levels. Insulin had no effect on cyclic AMP levels and did not alter the catecholamine-induced rise. The presence of Ca2+ in the extracellular fluid was not essential for the production of cyclic AMP, nor was it required for the catecholamine-induced rise in cyclic AMP. Neither glucagon, triiodothyronine or ouabain had any significant effect on cyclic AMP levels in the rat-heart slice.

Experimental myocardial ischemia. III. Protective effect of glucose on myocardial function

Abstract Glucose has been long known as an important substrate for muscle cells and a number of laboratories have demonstrated that carbohydrate metabolism can contribute significantly to energy production both in aerobic and anerobic heart muscle. It has been suggested that these findings may have additional application in localized myocardial ischemic and infarction. Accordingly, experiments were performed to determine the effect of glucose on the mechanical and electrical activity of the heart. Left ventricular pressure (LVP), left ventricular d p d t ( LVd p d t , left ventricular end diastolic pressure (LVEDP), and the incidence of ventricular premature beats (VPB) and ventricular fibrillation (VF) were determined before and after ligation of the anterior descending coronary artery in three different canine heart experimental models. Thirty minutes after ligation of the left anterior descending coronary artery, the mean left ventricular pressure and mean left ventricular d p d t in the control group had decreased by 85 ± 6% and 74 ± 5% respectively. Under similar conditions glucose treatment produces an increase in left ventricular pressure and left ventricular d p d t of 111 ± 5% and 123 ± 8% respectively. The simultaneously measured mean left ventricular end diastolic pressure was 7.2 ± 0.9 ml for the control group and 3.7 ± 1 for the glucose treated group. Eighty-three percent of the control dogs developed ventricular ectopic activity. Fifty-eight percent of the control hearts developed ventricular fibrillation. In contrast, only 10% of the glucose treated hearts demonstrated ventricular ectopic activity and only 10% developed ventricular fibrillation. Glucose, as a bolus, consistently improved myocardial contractility and prevented ventricular fibrillation even after serum osmolality and serum glucose levels had returned to normal. These results demonstrate that glucose has a protective effect on the electrical and mechanical function of the canine heart during acute segmental myocardial ischemia. These findings may have application in the treatment of acute myocardial infarction in man.

Comparison of the synthesis of the light and heavy chains of adult skeletal myosin

Abstract 1. Incorporation of amino acid into light chains and heavy chains of skeletal myosin has been studied by injection of radioactive leucine into adult rabbits. Light and heavy chain fractions were prepared by dissociation of myosin in 5 M guanidine hydrochloride. Three distinct polypeptide chain species were separated by chromatography on DEAE-Sephadex A-25 with molecular weights of 23 000 (light chain 1), 16 000 (light chain 2) and 12 000 (light chain 3) as determined by sodium dodecyl sulfate-acrylamide gel electrophoresis. 2. The specific activities of myosin light and heavy chains 30 min and 4 h after injection were about 20 and 60 %, respectively, of the values at 24 h. 3. Differences in pool sizes of myosin chains were evaluated by comparing the ratio of specific activities of chains at different times after labeling, since polypeptide chains with larger pools would be expected to become labeled more slowly. The ratio of light chains to heavy chains after 30 min was smaller than after 4 and 24 h, suggesting that the pool of uncombined light chains is larger than that of uncombined heavy chains. 4. Following 4- and 24-h labeling periods the ratio of light chain 1 to heavy chain specific activities was about 0.7, light chain 2 to heavy chain 1.1, and light chain 3 to heavy chain 1.8. It is concluded that these differences in radioactive leucine incorporation after longer labeling periods probably reflect actual differences in synthesis of myosin chains.

Ultra-Pure Polymerized Bovine Hemoglobin Blood Substitute: Effects on the Coronary Circulation

The effects of stroma-free hemoglobin (SFHgb) on the coronary circulation remain unclear. An intact canine model utilizing intracoronary adenosine to abolish the confounding effect of autoregulation was used to study maximal myocardial oxygen delivery during progressive hemodilution with polymerized bovine SFHgb. The circumflex coronary artery was instrumented with a flow probe, hydraulic constrictor, and proximal and distal catheters for adenosine infusion and distal pressure measurement, respectively. This preparation was used to generate diastolic coronary pressure-flow relations during maximal vasodilation. Maximal coronary conductance and maximal myocardial oxygen delivery were determined in two groups of 7 dogs each following hemodilution, first with 6% hetastarch (Control), followed by further hemodilution with ultra-pure, polymerized, bovine SFHgb. After hemodilution with SFHgb, maximal coronary flow increased slightly without evidence of coronary vasoconstriction. Since hemodilution with this material increases oxygen carrying capacity, maximal oxygen delivery is greater than Control, despite the very low canine hematocrit. These findings suggest: 1) SFHgb can provide adequate oxygen delivery to the myocardium despite extreme degrees of hemodilution, and 2) in this intact model, there is no evidence of adverse coronary vasomotion.