Umbilical catheter masquerading at echocardiography as a left atrial mass.

The case of a newborn who had an umbilical catheter inserted in the intensive care unit is discussed. This catheter was meant to be inserted into the umbilical artery, but was instead inadvertently inserted into the umbilical vein. It crossed a patent foramen ovale into the left atrium. This fact was not known at the time of echocardiographic evaluation. At echocardiography, abnormal echoes within the left atrium were seen. Findings were typical for a catheter within the heart, and the umbilical catheter was subsequently withdrawn. There is a potential for mistaking the echocardiographic findings for a left atrial abnormality and echocardiographers should be alert to this possibility.

The role of lysosomes and microtubules in cardiac protein degradation.

The mechanisms and regulatory factors involved in cardiac proteolysis are incompletely understood. Agents that interfere with lysosomal function (e.g., chloroquine, leupeptin, methyladenine) cause a 25-30% reduction in the overall rate of protein degradation. In the same hearts, however, the rate of myosin breakdown remains unchanged. Disaggregation of micro-tubules with colchicine is accompanied by a 15% reduction in the rate of degradation of total protein and of myosin. In the same hearts, the degradation of "organellar" protein, including mitochondrial cytochromes, is reduced by over 30%. Thus, it appears that the degradation of different classes of cardiac proteins may be accomplished and regulated by different processes. Lysosomes are important in overall proteolysis, but appear not to be involved in the regulation of myosin breakdown. Microtubules are also involved in the proteolytic process, and appear to be especially important for the breakdown of proteins from mitochondria and perhaps other organelles.

Direct anabolic effects of thyroid hormone on isolated mouse heart.

The direct effects of L-and D-triiodothyronine (T3) on cardiac protein metabolism were investigated using fetal mouse hearts in organ culture. This model allowed the production of "thyrotoxicosis" in isolated hearts in vitro in the absence of the usual systemic metabolic and hemodynamic effects of thyroid hormones. Hearts were studied during the first 24 h of T3 exposure in culture, before changes in beating rate due to T3 occurred. Phenylalanine release was decreased by 26 +/- 2.3% (P less than 0.001) by the optimal concentrations of T3 (10(-7) to 10(-6) M). Changes were similar in the presence or absence of insulin. D-T3 was also anabolic, decreasing phenylalanine release by 24 +/- 2.5% (P less than 0.001) at concentrations of 10(-6) to 10(-5) M. The L-isomer increased protein synthesis by 23 +/- 6.8% (P less than 0.05) and decreased protein degradation, as measured by phenylalanine release in the presence of cycloheximide, by 5 +/- 1.6% (P less than 0.01). The D-isomer also increased protein synthesis but had no measurable effect on protein degradation. We conclude that thyroid hormones can exert direct anabolic effects on heart in the absence of systemic hemodynamic and metabolic changes. These effects are mediated primarily through an acceleration of the rate of protein synthesis; in the case of L-T3, a small inhibition of proteolysis may also occur.

Changes in cardiac cathepsin B activity in response to interventions that alter heart size or protein metabolism: comparison with cathepsin D.

The specific activity of cardiac cathepsin B is significantly decreased by starvation and corticosteroid treatment in vivo, and by exposure of the heart in vitro to insulin, hydrocortisone and cycloheximide. Increases in cathepsin B activity occur following isoproterenol-induced cardiac damage in vivo and exposure in vitro to sucrose. Cathepsin B activity in heart is not changed during normal aging or in thyrotoxicosis. These responses are different from simultaneous changes in cardiac cathepsin D activity in several instances (starvation, corticosteroid treatment, aging and thyrotoxicosis). In the past, measurements of cathepsin D activity in heart have sometimes been considered to be representative of lysosomal proteinase activity in general and used as an index of cardiac lysosomal proteolytic capacity. The present results suggest that changes in cathepsin D do not necessarily reflect alterations in other lysosomal proteinases and may not serve as a valid indicator of overall lysosomal proteolytic capacity under all conditions.

Influence of chlorpromazine on lysosomal alterations during myocardial ischaemia.

Ligation of the circumflex artery of anaesthetised, open-chest rabbits caused a progressive increase in nonsedimentable cathepsin D activity in severely ischaemic myocardium and an anatomical redistribution of the enzyme from lysosomes into the cytosol, along with progressive ultrastructural signs of cellular damage and necrosis. Chlorpromazine pretreatment (15 mg X kg-1 intravenously) reduced the increase in nonsedimentable cathepsin D activity slightly, but no appreciable protective effect on the anatomical redistribution of the enzyme or the development of ultrastructural signs of necrosis could be detected. It is concluded that in this experimental model of myocardial infarction, high concentrations of chlorpromazine have a mild stabilising action on lysosomes, but the drug has minimal if any effect in protecting the heart from ischaemic damage.

Inhibition of cardiac proteolysis by colchicine. Selective effects on degradation of protein subclasses.

1. The effect of colchicine (2.5 microM) on cardiac protein turnover was tested with foetal mouse hearts in organ culture. 2. Colchicine had no effect on protein synthesis, but inhibited total protein degradation by 12-18%. Lumicolchicine, which lacks colchicine's ability to disaggregate microtubules, but shares its non-specific effects, did not alter protein degradation. 3. The colchicine-induced inhibition of protein degradation was accompanied by significant changes in cardiac lysosomal enzyme activities and distribution. 4. Colchicine inhibited the degradation of organellar proteins, including mitochondrial cytochromes, more than that of cytosolic proteins. 5. Colchicine decreased the rate of myosin degradation and the rate of proteolysis of the total protein pool to a similar extent. Since the regulation of myosin degradation does not involve lysosomes, this suggests that colchicine affects non-lysosomal as well as lysosomal pathways. 6. Release of branched-chain amino acids from colchicine-treated hearts was disproportionately decreased, suggesting that colchicine increased their metabolism. 7. It is concluded that colchicine, via its actions on microtubules, exerts important inhibitory effects on cardiac proteolysis. Colchicine is especially inhibitory to the degradation of organellar proteins, including mitochondrial cytochromes. Its inhibitory effects may be mediated in part via lysosomal mechanisms, but non-lysosomal mechanisms are probably involved as well.

Mechanisms of degradation of myofibrillar and nonmyofibrillar protein in heart.

The degradation of cardiac proteins is known to be altered by many physiological and pathological interventions, but the precise intracellular processes that regulate proteolysis and the relative roles of different proteolytic pathways in degrading different classes of protein remain poorly understood. Agents that interfere with lysosomal function produce major decreases in total protein breakdown; thus, lysosomes and lysosomal proteinases seem to be important in proteolysis. However, these same agents cause no change in the degradation of myofibrillar proteins, suggesting that this class of proteins is not dependent on lysosomal pathways for its turnover.

Intracellular disruption of rat heart lysosomes by leucine methyl ester: effects on protein degradation.

Perfusion of rat hearts with Krebs--Henseleit medium containing 10 mM L-leucine methyl ester leads to swelling of lysosomes and loss of lysosomal integrity within 30-60 min. No morphological changes can be detected in the nuclei, mitochondria, sarcoplasmic reticulum, or Golgi complex as a result of the treatment with leucine methyl ester, and the hearts continue to beat normally during the treatment period. Homogenates of rat hearts perfused with the methyl ester exhibit a decrease in the sedimentability of cathepsin D activity compared to controls, thus providing additional evidence for a loss of lysosomal integrity. Swelling and disruption of the lysosomes presumably occurs because of the extensive accumulation of leucine within the organelles resulting from the intralysosomal hydrolysis of the freely permeating methyl ester. The lysosomal dysfunction that occurs with exposure to leucine methyl ester produces a 30% decrease in cardiac protein degradation. These results provide an estimate of the contribution of lysosomes to total protein degradation in the rat heart, and they also suggest that the enzymes released as a result of lysosomal disruption are relatively inactive in hydrolyzing cellular constituents under the perfusion conditions used here. The use of amino acid methyl esters to produce rapid, specific loss of lysosomal integrity in situ provides an approach to the study of lysosomal function in intact cells.

Resistance to ischemic damage in hearts of starved rabbits: Correlation with lysosomal alterations and delayed release of cathepsin D.

Prolonged starvation produces dramatic changes both in the lysosomal properties of the heart and in its energy stores and, therefore, might be expected to alter some of the characteristic cardiac responses to ischemia. To test this possibility we ligated the circumflex coronary artery of rabbits that had been fed normally or starved for 6 days. Ultrastructural evidence of myocytic damage following 30 to 120 minutes of ischemia was much less severe in the starved animals than in the normally fed group. The development of signs of irreversible injury (e.g., osmiophilic densities in mitochondria) was delayed for 1 hour or more by starvation. A similar delay occurred in the biochemical redistribution of cathepsin D activity and in the cytoplasmic release of acid hydrolases from lysosomes and sarcoplasmic reticulum. These results indicate a marked protective effect of starvation against myocardial ischemia. In addition, both in starved and in fed animals, ischemically induced release of lysosomal enzymes was closely linked temporally to the development of subcellular damage.

Lysosomal alterations in hypoxic and reoxygenated hearts. II. Immunohistochemical and biochemical changes in cathepsin D.

Sublethal hypoxic injury in rat and rabbit hearts was accompanied by a biochemical redistribution of cathepsin D activity from the particulate to the supernatant fraction of the tissue homogenate, which was partially reversible on reoxygenation. Immunofluorescent staining for cathepsin D failed to reveal major anatomic release of the acid hydrolase until necrosis was present, suggesting that the earlier biochemical redistribution was primarily a result of increased lysosomal fragility during homogenization, with significant intracellular diffusion of the enzyme occurring only as irreversible damage took place. Hypoxia produced enlargement of both cathepsin-D-staining lysosomes and nonstaining vacuoles, as well as their aggregation. These changes were intensified during reoxygenation and recovery of reversibly damaged hearts, suggesting a possible role for the lysosomal-vacuolar apparatus in myocytic repair following hypoxic injury.

Effect of thyrotoxicosis and recovery on myocardial protein balance.

Thyroid hormone, given in vivo or in vitro, exerts an anabolic effect on the heart. The hypertrophy that is produced by daily thyroxine injections in vivo is mediated primarily by an increase in protein synthesis. The changes in protein balance seem to be mediated at least in part by a direct action of thyroid hormone on heart cells, independent of secondary changes in hemodynamic or neurohumoral factors (although these might well contribute to the final effects in vivo, of course). The cardiac catabolism that accompanies regression of thyroxine-induced hypertrophy is characterized by a marked reduction in protein synthesis, not by an acceleration of protein breakdown.

Inhibition of inotropic effect of hyperosmotic mannitol by lactate in vitro.

Isolated, isometrically contracting cat papillary muscles were used to evaluate the inotropic interactions of lactic acidosis, hypercarbic acidosis, and lactate ion with hypertonic mannitol. These studies have documented that both lactic acidosis (pH less than 7.0) and lactate ion at a normal pH inhibit the inotropic effect of hyperosmotic mannitol in vitro. In contrast, hypercarbic acidosis does not prevent the inotropic effect of mannitol. Inhibition by lactic acid of mannitol's effects on contractility persists in the presence of beta-receptor blockade. The results suggest that inhibition by severe lactic acidosis of the direct inotropic effect of hyperosmolality in isolated cardiac muscle is mediated by lactate ion rather than acidosis per se.

Negative inotropic influence of hyperosmotic solutions on cardiac muscle.

In cardiac muscle, moderate degrees of hyperosmolality of the type encountered physiologically or clinically (i.e., less than 200 mosM above control) characteristically exert a positive inotropic effect, which presumably is mediated by increased Ca2+ availability for binding to troponin. In contrast, skeletal muscle displays significant contractile depression on exposure to hyperosmotic solutions, even at mild degrees of hypertonicity. To determine whether a similar potential for hyperosmolarity-induced depression also exists in cardiac muscle, right ventricular papillary muscles from cats were exposed to hypertonic solutions of mannitol or sucrose under circumstances in which positive inotropic effects were precluded by prior exposure to a bathing solution of 4.0 mM Ca2+ and paired electrical stimulation to maximize intracellular Ca2+ before addition of the hyperosmotic substances. In contrast to their usual positive inotropic effects, hypertonic solutions under these conditions caused cardiac depression at all osmolarities tested. Developed tension and its maximal rate of development (dT/dt) decreased by 18% at 50 mosM above control, by 30% at 100 mosM, by 36% at 150 mosM, and by 42% at 200 mosM (P less than 0.01 for all). Time to peak tension and resting tension were not changed significantly. When the muscles were returned to control solutions, tension development also returned toward normal. The data are compatible with the hypothesis that, within the range tested, all degrees of hyperosmolarity exert a significant negative inotropic influence on cardiac muscle, as is true in skeletal muscle; manifestation of this effect of increased tonicity normally would be obscured at low degrees of hyperosmolality, however, by an overriding positive influence that is absent in skeletal muscle.

Importance of calcium in the inotropic effect of hyperosomotic agents, norepinephrine, paired electrical stimulation, and treppe.

The data obtained from these studies demonstrate that the inotropic effect of hyperosmolar mannitol and sucrose and of paired electrical stimulation is critically influenced by extracellular calcium concentration. The inotropic effect of norepinephrine is not prevented by maximal functional extracellular calcium concentrations. Inhibition of systolic calcium flux at the cell membrane by D600 does not prevent the inotropic effect of hyperosmolar mannitol or of paired electrical stimulation but it does prevent the inotropic effect of hyperosmolar intropic effect of treppe. Thus, intracellular calcium regulation appears to be of major importance in the inotropic effect in isolated cardiac muscle of mannitol and paired pacing while systolic calcium flux at the cell membrane appears to be of major importance in the inotropic effect of treppe.