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Biomedical subjects

F G Spinale

Publications and source records attributed to F G Spinale.

At least 127 records · Page 7Linked to original sources
PubMed1995

Differential effects of protamine sulfate on myocyte contractile function with left ventricular failure.

OBJECTIVES: This project tested two fundamental hypotheses: 1) Protamine sulfate has a direct and negative effect on myocyte contractile processes; 2) the negative effects of protamine on myocyte contractility will be enhanced in the setting of chronic left ventricular dysfunction. BACKGROUND: An increasing number of patients undergoing cardiac and vascular surgical procedures have underlying chronic left ventricular dysfunction. Protamine sulfate is commonly required during these surgical procedures but has been associated with left ventricular dysfunction. However, it is not known whether protamine may have a direct and selective effect on myocyte contractility in the setting of chronic left ventricular dysfunction. METHODS: This study examined the direct effects of protamine on isolated myocyte contractile function in 10 control pigs and 10 pigs with dilated cardiomyopathy induced by supraventricular tachycardia (rapid atrial pacing at 240 beats/min for 3 weeks). Myocyte contractile function was measured by videomicroscopy at baseline and with 10, 20, 40 or 80 micrograms/ml of protamine. In a second series of experiments, myocytes were preincubated with protamine and then stimulated with the beta-adrenergic agonist isoproterenol (25 nmol/liter). RESULTS: In the presence of 20 micrograms/ml of protamine, myocyte contractile function was unaffected in the control group but decreased by 40% from baseline values in the supraventricular tachycardia group. With 10 micrograms/ml of protamine, myocyte beta-adrenergic responsiveness was reduced by 25% in the supraventricular tachycardia group with no change in the control group. In the presence of 40 and 80 micrograms/ml of protamine, myocyte contractile function decreased in both groups. However, 40 micrograms/ml of protamine caused a more pronounced decline in myocyte function and beta-adrenergic responsiveness in the supraventricular tachycardia group. CONCLUSIONS: An increased sensitivity to the depressive effects of protamine on myocyte contractile function and beta-adrenergic responsiveness occurred in this model of chronic left ventricular dysfunction. These results suggest that patients with underlying cardiac disease may have an increased susceptibility to a sudden compromise of left ventricular contractile performance after protamine administration.

Animals↗
PubMed1995

Direct effects of thrombin on myocyte contractile function.

Cardiopulmonary bypass activates the clotting cascade, resulting in elevated circulating levels of thrombin. In light of the fact that the function of a wide variety of cell types is modulated by thrombin, we hypothesized that thrombin may have a direct effect on myocyte function. Isolated left ventricular myocyte contractile function was measured from 6 adult dogs using videomicroscopy at baseline and after increasing concentrations of thrombin (1 to 10 U/mL). Indices of myocyte contractile function were reduced in a dose-dependent manner in the presence of increasing concentrations of thrombin. For example, myocyte percent shortening fell by 18% with 1 U/mL thrombin and by 43% with 2 U/mL thrombin. The addition of hirudin, a highly selective thrombin inhibitor, completely blocked the effects of thrombin on myocyte contractile function. beta-Adrenergic agonists are commonly used in the early post-cardiopulmonary bypass period. Accordingly, a final set of experiments examined the effects of thrombin on myocyte beta-adrenergic responsiveness using isoproterenol (25 nmol/L). In myocytes preincubated with 1 U/mL thrombin, myocyte beta-adrenergic responsiveness was significantly reduced. For example, in the presence of 1 U/mL thrombin, myocyte velocity of shortening fell by 25% from isoproterenol alone values. The results from the present study provide evidence that thrombin has a direct negative effect on steady-state contractile function and beta-adrenergic responsiveness in adult mammalian ventricular myocytes. These findings suggest that thrombin may be an additional contributory factor toward the transient left ventricular dysfunction that has been observed after cardiopulmonary bypass.

Animals↗
PubMed1995

3,5,3' Triiodo-L-thyronine pretreatment with cardioplegic arrest and chronic left ventricular dysfunction.

BACKGROUND: The active form of thyroid hormone, T3, may be an important determinant of left ventricular (LV) function after hypothermic cardioplegic arrest and rewarming, particularly in patients with preexisting LV dysfunction. Thus, the present project tested the hypothesis that T3 pretreatment will improve myocyte contractile performance after hypothermic cardioplegic arrest and rewarming in the setting of chronic LV dysfunction. METHODS: Control LV porcine myocytes (n = 160) and cardiomyopathic LV (rapid pacing for 3 weeks at 240 beats/min) myocytes (n = 100) were treated with or without 80 pmol/L T3. Myocytes then were maintained in normothermic conditions (2 hours at 37 degrees C in media) or exposed to hypothermic cardioplegic arrest ([K+], 24 mmol/L; 2 hours at 4 degrees C) with subsequent rewarming. RESULTS: After cardioplegic arrest and rewarming, T3 pretreatment increased myocyte velocity of shortening by 41% in control myocytes and by 35% in cardiomyopathic myocytes when compared to untreated myocytes. Furthermore, T3 pretreatment followed by beta-adrenergic receptor stimulation with isoproterenol (25 nmol/L) improved myocyte velocity of shortening by 24% in control myocytes and 90% in cardiomyopathic myocytes after hypothermic cardioplegic arrest and rewarming, as compared with untreated myocytes. CONCLUSIONS: In summary, this study provides evidence to suggest that preemptive treatment with T3 may improve LV pump function and beta-adrenergic responsiveness after hypothermic cardioplegic arrest and rewarming in patients with underlying LV dysfunction.

Animals↗
PubMed1995

Myocyte electrophysiological properties following the development of supraventricular tachycardia-induced cardiomyopathy.

Chronic supraventricular tachycardia (SVT) causes left ventricular (LV) dilatation and dysfunction, diminished myocyte contractile function, and abnormalities in sarcolemmal receptor systems. We hypothesized that changes in myocyte action potential characteristics and L-type Ca2+ channel (Ca2+ channel) function, which are major determinants of myocyte contractile processes, would occur with SVT cardiomyopathy. LV function and isolated myocyte contractile function were examined in 11 pigs with SVT cardiomyopathy (pace 240 bpm; 3 weeks) and 11 control pigs. With chronic SVT, LV fractional shortening fell and myocyte shortening velocity was reduced compared to controls (11 +/- 2 v 37 +/- 2%, P < 0.0001; and 32.5 +/- 1.2 v 55.7 +/- 1.6 microns/s, P < 0.0001, respectively). Isolated myocyte action potential upstroke velocity and amplitude were reduced with SVT cardiomyopathy compared to controls (92.8 +/- 4.8 v 129.5 +/- 3.1 V/s, P < 0.0001; and 98.2 +/- 2.2 v 110.3 +/- 1.3 mV, P < 0.0001, respectively). the duration of the myocyte action potential, defined as the time to 90% repolarization, was prolonged with SVT cardiomyopathy compared to controls (201.7 +/- 5.9 v 169.1 +/- 6.8 ms, P = 0.002). These specific abnormalities in the indices of myocyte contractile function and action potential characteristics which occurred with SVT cardiomyopathy were not normalized following beta-adrenergic receptor stimulation. In order to determine a potential mechanism for the changes in myocyte contractile function and action potential characteristics with SVT cardiomyopathy, Ca2+ channel function was examined in control and SVT myocytes. In SVT myocytes, peak L-type Ca2+ current (ICa) normalized to membrane capacitance and the Ca2+ channel inactivation time constant were reduced compared to controls (-2.30 +/- 0.24 v -3.79 +/- 0.28 pA/pF, P = 0.0001; and 104.0 +/- 10.8 v 199.9 +/- 27.4 ms, P = 0.005, respectively). The abnormalities in Ca2+ channel function with SVT cardiomyopathy persisted in myocytes with equivalent membrane capacitances and were not normalized with beta-adrenergic receptor stimulation. In conclusion, findings from the present study suggest that fundamental abnormalities in myocyte electrical events (action potential) and ionic flux (Ca2+ channel function) are contributory mechanisms for the depressed myocyte contractile function with SVT cardiomyopathy.

Action Potentials↗
PubMed1995

The direct effects of 3,5,3'-triiodo-L-thyronine (T3) on myocyte contractile processes. Insights into mechanisms of action.

Administration of 3,5,3'-triiodo-L-thyronine (T3) has recently been suggested to acutely improve left ventricular performance. However, the cellular and molecular mechanisms responsible for this improvement in left ventricular function with T3 remained unknown. Accordingly, the present study examined the direct effects of T3 administration on myocyte contractile function and the sarcolemmal systems that might potentially contribute to these effects. In isolated porcine left ventricular myocytes (n = 81), velocity of shortening increased in the presence of 80 pmol/L T3 compared with that in untreated myocytes (117.0 +/- 5.0 versus 77.3 +/- 3.3 microns/sec, p < 0.05). In a separate series of experiments (n = 29), myocyte velocity of shortening increased in the presence of both T3 and beta-adrenergic receptor stimulation (25 nmol/L isoproterenol) to greater than that with beta-adrenergic receptor stimulation alone (274.3 +/- 16.9 versus 203.7 +/- 16.2 microns/sec, p < 0.05). Cyclic adenosine monophosphate generation was next examined in isolated myocyte preparations (n = 9). In the presence of T3, no significant increase in cyclic-adenosine monophosphate generation was observed compared with that in untreated myocytes (39.1 +/- 8.3 versus 24.7 +/- 5.8 fmols/myocyte, p = 0.17). However, in the presence of both T3 and beta-adrenergic receptor stimulation, cyclic-adenosine monophosphate generation increased significantly to greater than that with beta-adrenergic receptor stimulation alone (224.4 +/- 61.1 versus 120.1 +/- 35.5 fmoles/myocyte, p < 0.05). Because cyclic-adenosine monophosphate modulates intracellular Ca2+ processes, L-type Ca+2 channel current (patch clamp methods; -picoamp/picofarad, n = 15) and peak intracellular Ca+2 levels (fura 2 ionic measurement, n = 47) were next measured. In the presence of T3, a shift in the activation voltage at peak L-type Ca+2 channel current was observed from baseline (5.5 +/- 1.4 versus 9.0 +/- 1.0 mV, p < 0.05). Furthermore, in the presence of both T3 and beta-adrenergic receptor stimulation, peak L-type Ca+2 channel current (8.9 +/- 0.7 versus 6.3 +/- 1.0 mV, p < 0.05) and peak intracellular Ca+2 levels (189.9 +/- 8.4 versus 171.7 +/- 8.3 nmol/L, p < 0.05) increased compared with values obtained with beta-adrenergic receptor stimulation alone. Important findings from the present study were twofold: (1) T3 improved myocyte contractile processes through a cyclic-adenosine monophosphate-independent mechanism and (2) T3 potentiated the effects of beta-adrenergic receptor stimulation transduction by increasing cyclic-adenosine monophosphate production, L-type Ca+2 channel current, and Ca+2 availability to the myocyte contractile apparatus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Pretreatment with 3,5,3'triiodo-L-thyronine (T3). Effects on myocyte contractile function after hypothermic cardioplegic arrest and rewarming.

Circulating levels of 3,5,3'triiodo-L-thyronine are depressed after cardiopulmonary bypass and have been implicated to play a contributory role in the alterations in left ventricular function after hypothermic cardioplegic arrest and rewarming. The central hypothesis of the present study was that pretreatment of isolated myocytes with triiodothyronine will have a direct and beneficial effect on contractile performance after hypothermic cardioplegic arrest and rewarming. Contractile function in isolated pig left ventricular myocytes was examined by video microscopy after the following treatment protocols: (1) 37 degrees C incubation in medium (normothermia) for 2 hours with triiodothyronine followed by a 2-hour normothermic incubation with no triiodothyronine, (2) 4 hours of normothermic incubation with no triiodothyronine, (3) normothermic incubation for 2 hours with triiodothyronine followed by 2 hours of hyperkalemic, hypothermic cardioplegic arrest ([K+]:24 mmol/L; 4 degrees C) and subsequent rewarming, and (4) normothermic incubation for 2 hours with no triiodothyronine followed by 2 hours of hyperkalemic, hypothermic cardioplegic arrest and rewarming. Two hours of normothermia with triiodothyronine increased myocyte contractile function by 30% compared with values in untreated control myocytes, and this increase persisted after a subsequent 2-hour incubation under normothermic conditions with no triiodothyronine. For example, myocyte velocity of shortening in triiodothyronine-pretreated myocytes was 84 +/- 4.9 microns/sec compared with 62 +/- 2.8 microns/sec in control myocytes (p < 0.05). Cardioplegic arrest and subsequent rewarming caused a significant reduction in myocyte velocity of shortening from normothermic values (37 +/- 3.4 microns/sec, p < 0.05). However, in myocytes pretreated with triiodothyronine, myocyte contractile function was significantly higher after hypothermic cardioplegic arrest and rewarming (54 +/- 2.5 microns/sec, p < 0.05). In a second series of experiments, beta-adrenergic responsiveness was examined after pretreatment with triiodothyronine. In the presence of the beta-adrenergic agonist isoproterenol (25 nmol/L), myocyte contractile function was increased by 26% in the triiodothyronine-treated myocytes compared with that in untreated control myocytes. This enhanced beta-adrenergic responsiveness with triiodothyronine pretreatment persisted with subsequent exposure to hypothermic cardioplegic arrest and rewarming. In summary, triiodothyronine pretreatment caused an increase in myocyte contractile function and beta-adrenergic responsiveness under normothermic conditions and after hypothermic cardioplegic arrest and rewarming. Thus the present study provides direct evidence to suggest that preemptive treatment with triiodothyronine may improve left ventricular contractile performance after hypothermic cardioplegic arrest and rewarming.

Animals↗
PubMed1995

Protamine use during peripheral vascular surgery: a prospective randomized trial.

PURPOSE: One hundred twenty patients undergoing aortic reconstruction (40), infrainguinal bypass (49), and carotid endarterectomy (31) were prospectively enrolled into a double-blind randomized trial to investigate the utility of routine heparin reversal with protamine. METHODS: All patients underwent systemic heparinization with 90 U/kg body weight during operation and after revascularization were randomized to receive either protamine or saline solution for heparin reversal. Blood loss was measured throughout the surgical procedure, and indexes of coagulation and the requirement for blood and blood products were documented during operation and the first 24 hours after operation. RESULTS: Plasma heparin concentration, partial thromboplastin time, and activated clotting time were significantly higher (p < 0.05) in those receiving saline solution at 20 minutes and 1 hour after administration. Total surgical blood loss was not significantly different between study groups. No significant differences were found in blood product requirement, intravenous fluid administered, hematocrit, or wound hematomas between groups at 24 hours. In addition, no difference was seen in the surgeon's subjective intraoperative assessment of hemostasis after administration of either study drug. Furthermore, after study drug administration protamine was associated with a deleterious effect on subsequent intraoperative blood loss (318 +/- 33 ml vs 195 +/- 18 ml, p < 0.05). CONCLUSIONS: Although protamine effectively reverses heparin anticoagulation, its routine use after elective peripheral vascular surgical reconstruction does not appear to provide any clinical benefit.

Aged↗
PubMed1995

The direct and interactive effects of phosphodiesterase inhibition and beta-adrenergic stimulation on myocyte contractile function after hypothermic cardioplegic arrest.

The direct and interactive effects of phosphodiesterase inhibition (PDEI) and beta-adrenergic receptor (beta AR) stimulation on isolated myocyte contractile function were examined after hypothermic, hyperkalemic, cardioplegic arrest (HHCA) and under normothermic conditions. Left ventricular (LV) myocytes were isolated from porcine hearts and myocyte contractile function was measured under normothermic conditions (37 degrees C in standard media) and after HHCA (2 h at 4 degrees C in Ringer's solution with 24 mEq KCl) with subsequent rewarming. Myocytes were then randomly assigned to treatment with the beta AR agonist isoproterenol (25 nM), the phosphodiesterase inhibitor amrinone (50 microM), or a combination of these compounds and contractile function measurements repeated. Baseline myocyte contractile function was reduced by 32% after HHCA. Isoproternol alone increased myocyte contractile function more than 100% under both normothermic conditions and after HHCA, whereas amrinone alone significantly (60%) improved myocyte contractile function only after HHCA. Amrinone preincubation followed by isoproterenol improved contractile function after HHCA to a greater extent than all other treatment protocols. In contrast, combination treatment under normothermic conditions did not augment myocyte contractile function relative to isoproterenol alone. These findings suggest that amrinone has differential effects on contractile processes. Moreover, the marked improvement of contractile function after HHCA with PDEI pretreatment followed by beta AR stimulation may have implications in treatment strategies for improving myocardial function after cardiopulmonary bypass and provide insight into contractile dysfunction after HHCA.

Adrenergic beta-Agonists↗
PubMed1995

Myocyte contractile responsiveness after hypothermic, hyperkalemic cardioplegic arrest. Disparity between exogenous calcium and beta-adrenergic stimulation.

BACKGROUND: Acute left ventricular dysfunction is commonly encountered after hypothermic, hyperkalemic cardioplegic arrest (HHCA) and often requires inotropic intervention for successful separation from cardiopulmonary bypass. However, the basic mechanisms involved in depressed left ventricular function and the cellular basis for the differential effects of inotropic drugs after HHCA are unknown. Accordingly, the goal of this study was to determine the effects of calcium (Ca2+) and beta-adrenergic receptor agonists (beta AR) stimulation on isolated myocyte contractile function after HHCA. METHODS: Myocytes were isolated from the left ventricle of nine pigs and randomly assigned to one of the following treatment groups: (1) normothermic, control: incubation in oxygenated cell culture media for 2 h at 37 degrees C; and (2) cardioplegia: incubation in 4 degrees C crystalloid cardioplegia for 2 h, followed by rewarming. Steady-state myocyte contractile function was measured after pulse stimulation at baseline, in the presence of extracellular Ca2+ (3-10 mM), and in the presence of the beta AR agonist isoproterenol (2-100 nM). Myocyte profile surface area was measured for both normothermic myocytes and myocytes after HHCA. In a separate set of experiments, myocyte contractile function also was documented after 2 h of hypoxic conditions with both normothermic incubation and HHCA, in the presence and absence of beta AR stimulation. RESULTS: Baseline myocyte contractile function was significantly less in the cardioplegia group compared to control. Extracellular Ca2+ produced a dose-dependent significant increase in myocyte contractile function in the normothermic control group, whereas increased extracellular Ca2+ only minimally increased myocyte contractile function in the cardioplegia group. A dose-dependent, significant increase in myocyte contractile function was observed in both groups after beta AR stimulation by isoproterenol; however, myocyte contractile function in the cardioplegia group was decreased compared to the control group. Hypoxia under normothermic conditions significantly reduced myocyte contractile function, myocyte relaxation, and beta-adrenergic responsiveness. Hypoxia in combination with cardioplegic arrest compounded the negative effects on contractile processes but did not further impair beta-adrenergic responsiveness. Myocyte profile surface area was significantly increased after HHCA. CONCLUSIONS: The minimal improvement in myocyte contractile function after HHCA with increased extracellular Ca2+ suggests that Ca2+ depletion is not the primary mechanism for depressed myocyte contractility after HHCA. On the other hand, because beta AR administration improved myocyte contractile function after HHCA, the cellular basis for the effects of beta AR stimulation after HHCA is probably not increased myocyte Ca2+ but rather alternative mechanisms, such as changes in myofilament sensitivity to Ca2+. These results also suggest that the abnormalities in left ventricular function after HHCA result from the direct effects of hyperkalemic induced electromechanical uncoupling as well as relative hypoxic conditions.

Adrenergic beta-Agonists↗
PubMed1995

LV and myocyte structure and function after early recovery from tachycardia-induced cardiomyopathy.

Left ventricular (LV) function and mass were measured in six conscious dogs at weekly intervals during the progression of tachycardia-induced dilated cardiomyopathy (DCM) and during a 1-mo recovery period from DCM (post-DCM). LV end-diastolic volume and LV wall stress increased and LV ejection fraction decreased with each week of pacing. Despite the increased LV wall stress, LV mass did not change during the progression of tachycardia DCM. One week post-DCM resulted in an improved LV ejection fraction and normalization of neurohormonal profiles. However, 1 wk post-DCM was accompanied by a 26% increase in LV mass and persistent LV chamber dilation. Isolated myocyte function was examined and compared with that in six normal control dogs. Myocyte percent and myocyte velocity of shortening were 19 and 32% lower, respectively, in the post-DCM group compared with controls. Thus termination of the tachycardia subsequent to the development of DCM resulted in persistent LV chamber dilation and abnormalities in myocyte contractile function. The improved LV pump function with early recovery from tachycardia-induced DCM was mediated by LV hypertrophy and a subsequent reduction in LV wall stress rather than a normalization of LV geometry and myocyte contractile function.

Animals↗
PubMed1995

Effects of chronic supraventricular pacing tachycardia on relaxation rate in isolated cardiac muscle cells.

Chronic supraventricular pacing tachycardia (SVT) causes abnormalities in both ventricular and cellular relaxation. The mechanisms causing these abnormalities have not been fully determined. To examine two of the possible mechanisms, a decrease in restoring force or an impairment of the intrinsic myocardial relaxation process, cardiocytes were enzymatically isolated from the left ventricle of pigs subjected to left atrial pacing at 240 beats/min for 3 wk and normal control pigs. SVT caused a decrease in the extent of cardiocyte shortening and the velocity of cardiocyte lengthening. To determine whether the changes in the relaxation velocity merely reflected a concomitant decrease in the extent of cardiocyte shortening (and a resultant decrease in restoring forces) or, in addition, reflected impairment in intrinsic relaxation properties, the relation between cardiocyte relaxation velocity and cardiocyte shortening extent was examined. There was a direct relation between relaxation velocity and shortening extent in both control and SVT cardiocytes. However, SVT decreased the relaxation velocity at any common extent of shortening and decreased the slope of the direct relation (slope 5.91 in control vs. 3.51 s-1 in SVT, P < 0.05). Therefore, these data suggested that SVT caused a primary impairment in the intrinsic myocardial relaxation process independently of a decrease in restoring force.

Animals↗
PubMed1995

Contractile and cytoskeletal content, structure, and mRNA levels with tachycardia-induced cardiomyopathy.

Chronic supraventricular tachycardia (SVT)-induced cardiomyopathy is associated with left ventricular (LV) dilatation, increased wall stress, neurohormonal activation, and no change in LV mass. To determine mechanisms for changes in LV geometry and function with SVT cardiomyopathy, LV and myocyte function, contractile protein content and mRNA levels, and cytoskeletal protein structure and mRNA levels were examined in 12 pigs with SVT cardiomyopathy (paced at 240 beats/min for 3 wk) and in 12 controls. With SVT cardiomyopathy, LV fractional shortening fell by 61%, and end-diastolic dimension increased by 42%, with no change in LV mass-to-body weight ratio (3.36 +/- 0.15 vs. 3.14 +/- 0.13 g/kg). Myocyte contractile function was reduced by 33%, myocyte length was increased by 28%, and cross-sectional area was decreased by 19% with SVT cardiomyopathy. Total protein, myosin heavy chain (MHC), and actin appeared unchanged with SVT cardiomyopathy at the LV or myocyte level. Moreover, there was no change in mRNA levels for MHC (0.57 +/- 0.05 vs. 0.59 +/- 0.09 mRNAOD/rRNAOD) or cardiac alpha-actin (0.58 +/- 0.08 vs. 0.58 +/- 0.04 mRNAOD/rRNAOD) with SVT cardiomyopathy. In contrast, mRNA levels for specific cytoskeletal proteins were significantly increased with SVT cardiomyopathy, and immunofluorescent localization of contractile and cytoskeletal proteins in isolated myocytes revealed alterations in cytoskeletal architecture. Thus changes in LV and myocyte geometry with SVT cardiomyopathy were associated with no change in contractile protein content or mRNA at the chamber or myocyte level. Furthermore, increased cytoskeletal protein abundance and mRNA and reorientation of cardiocyte cytoarchitecture may have contributed to the LV and myocyte remodeling with SVT cardiomyopathy.

Actins↗
PubMed1995

Inhibition of collagen cross-linking: effects on fibrillar collagen and ventricular diastolic function.

The fibrillar collagen network is postulated to be a primary determinant of left ventricular diastolic stiffness. This hypothesis was tested by examining the structural and physiological effects of a reduction in fibrillar collagen content and cross-linking in the intact left ventricle. Collagen cross-linking was inhibited by treating five normal adult pigs with beta-aminopropionitrile (BAPN; 10 g/day po) for 6 wk; five normal untreated pigs served as controls. Left ventricular volume, mass, and function were determined by simultaneous echocardiography and catheterization. Chamber stiffness, defined by pressure vs. volume data, and myocardial stiffness, defined by stress vs. dimension data, were determined from variably loaded beats during dextran infusion. Collagen distribution (% area) and integrity (% confluence) were determined by light microscopy. Collagen content was measured by hydroxyproline assay, and collagen cross-linking was measured by salt extraction. BAPN decreased collagen distribution (% area decreased from 12 +/- 1% in control to 7 +/- 1% in BAPN, P < 0.05), collagen integrity (% confluence decreased from 8 +/- 1% in control to 4 +/- 1% in BAPN, P < 0.05), collagen content (from 36 +/- 2 mg/g dry wt in control to 27 +/- 2 mg/g dry wt in BAPN, P < 0.05), and collagen cross-linking (extractable collagen increased from 21 +/- 2% in control to 28 +/- 2% in BAPN, P < 0.05). BAPN decreased chamber stiffness (0.13 +/- 0.02 in control to 0.06 +/- 0.01 in BAPN, P < 0.05) and myocardial stiffness (10.4 +/- 0.5 in control to 6.6 +/- 0.5 in BAPN, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Aminopropionitrile↗
PubMed1994

Direct effects of acute administration of 3, 5, 3' triiodo-L-thyronine on myocyte function.

Recent studies have suggested that acute administration of 3, 5, 3' triiodo-L-thyronine (T3) may increase ventricular performance; however, the direct cellular effects of acute T3 administration are not understood. The objectives of this study were to determine (1) whether T3 acts directly on the cardiac muscle cell (myocyte) itself, and (2) whether T3 acts independently of the myocyte beta-adrenergic receptor. Accordingly, isolated myocyte function was examined using video-microscopy in normal porcine myocytes (n = 60) in the control state and in the presence of increasing T3 concentrations (10 to 500 pmol/L). T3 caused myocyte shortening extent, shortening velocity, and lengthening velocity to increase in a dose-dependent manner. For example, shortening velocity increased from 49.2 +/- 4.3 microns/s at baseline to 66.5 +/- 6.1 microns/s with 100 pmol/L T3 (p < 0.05). beta-Adrenergic stimulation with 25 nmol/L isoproterenol increased shortening velocity to 97.6 +/- 5.7 microns/s; isoproterenol with T3 increased shortening velocity further to 168.5 +/- 10.9 microns/s. Analysis of variance revealed that this increase with T3 was independent of and additive to the beta-adrenergic receptor system. In summary, T3 caused a dose-dependent increase in myocyte contractile performance, and these effects were independent of and additive to beta-adrenergic receptor stimulation. Thus, acute T3 administration may provide a novel modality to improve left ventricular contractile function independent of the beta-adrenergic receptor system.

Animals↗
PubMed1994

Effects of protamine on myocyte contractile function and beta-adrenergic responsiveness.

The use of protamine sulfate in patients has been associated with severe circulatory collapse and myocardial failure. However, the exact mechanisms responsible for these reactions to protamine remain unclear. Accordingly, we examined the effect of protamine on isolated myocyte contractile function. Indexes of isolated myocyte contractile function, percent shortening, and velocity of shortening were examined using videomicroscopy. Porcine cardiocytes (n = 75) were studied at baseline and in the presence of 80 micrograms/mL protamine. In addition, myocyte function was examined sequentially, first during treatment with 8 IU/mL heparin and then after the addition of a protamine dose sufficient to completely bind the heparin. The binding of heparin and protamine resulted in the formation of a heparin-protamine complex. The protamine concentration of 80 micrograms/mL is approximately equal to the serum concentration of protamine obtained in patients when administered in a dose of 5 mg/kg. In the presence of 80 micrograms/mL protamine, both percent shortening and velocity of shortening fell by more than 32% from baseline values (p < 0.05). The presence of either heparin alone or the heparin-protamine complex resulted in no change in baseline myocyte contractile measurements. Furthermore, to examine the effect of protamine on myocyte beta-adrenergic responsiveness a second series of experiments were performed. Myocyte contractile function was measured when 25 nmol/L isoproterenol was added to each of the protocols above. The presence of 80 micrograms/mL protamine resulted in a significant blunting of myocyte beta-adrenergic responsiveness. The presence of either heparin alone or the heparin-protamine complex resulted in no change in myocyte beta-adrenergic responsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Cellular and molecular alterations in the beta adrenergic system with cardiomyopathy induced by tachycardia.

OBJECTIVE: The aim was to examine the relationship between changes in myocyte function to changes in protein and mRNA content of components of the beta adrenergic system with tachycardia induced cardiomyopathy. METHODS: Contractile function and beta adrenergic responsiveness were measured in isolated myocytes from control pigs (n = 6) and in pigs subjected to three weeks of pacing induced supraventricular tachycardia (n = 6). beta Receptor density and affinity, the relative content of the stimulatory (Gs) and inhibitory (Gi) subunits of the G protein complex, and adenylate cyclase activity were determined from sarcolemmal preparations. In order to determine whether these changes were accompanied by alterations in steady state mRNA levels for specific components of the beta adrenergic system, mRNA content for the beta 1 adrenergic receptor and the G alpha s and G alpha i2 subunits of the G protein complex was measured. RESULTS: Chronic supraventricular tachycardia caused a 36% increase in left ventricular end diastolic dimension and a 61% decrease in left ventricular fractional shortening compared to controls. The velocity of isolated myocyte shortening was 50% lower in myocytes from hearts with tachycardia cardiomyopathy than in control myocytes. In the presence of 50 nM isoprenaline or 2 microM forskolin, the velocity of myocyte shortening was 65% lower in the myopathic myocytes than in the controls. With the development of tachycardic cardiomyopathy, beta adrenergic receptor density fell by 25% with no change in affinity, Gs decreased by 35%, and Gi increased by over 50% compared to controls. Basal adenylate cyclase activity and isoprenaline and forskolin stimulated adenylate cyclase activity fell by over 50% with supraventricular tachycardia compared to controls. The relative content of G alpha i2 mRNA increased threefold with the development of tachycardic cardiomyopathy with no change in the relative abundance of mRNA for the beta 1 receptor or G alpha s when compared with controls. CONCLUSIONS: The changes in myocyte beta adrenergic responsiveness with the development of tachycardic cardiomyopathy are due to alterations in cellular mechanisms (decreased beta receptor and Gs density, increased Gi) and in molecular mechanisms (increased Gi mRNA content).

Adenylyl Cyclases↗
PubMed1994

Effects of chronic beta-adrenergic blockade on the left ventricular and cardiocyte abnormalities of chronic canine mitral regurgitation.

The mechanism by which beta blockade improves left ventricular dysfunction in various cardiomyopathies has been ascribed to improved contractile function of the myocardium or to improved beta-adrenergic responsiveness. In this study we tested two hypotheses: (a) that chronic beta blockade would improve the left ventricular dysfunction which develops in mitral regurgitation, and (b) that an important mechanism of this effect would be improved innate contractile function of the myocardium. Two groups of six dogs with chronic severe mitral regurgitation were studied. After 3 mo both groups had developed similar and significant left ventricular dysfunction. One group was then gradually beta-blocked while the second group continued to be observed without further intervention. In the group that remained unblocked, contractile function remained depressed. However, in the group that received chronic beta blockade, contractile function improved substantially. The contractility of cardiocytes isolated from the unblocked hearts and then studied in the absence of beta receptor stimulation was extremely depressed. However, contractility of cardiocytes isolated from the beta-blocked ventricles was virtually normal. Consistent with these data, myofibrillar density was much higher, 55 +/- 4% in the beta-blocked group vs. 39 +/- 2% (P < 0.01) in the unblocked group; thus, there were more contractile elements to generate force in the beta-blocked group. We conclude that chronic beta blockade improves left ventricular function in chronic experimental mitral regurgitation. This improvement was associated with an improvement in the innate contractile function of isolated cardiocytes, which in turn is associated with an increase in the number of contractile elements.

Adrenergic beta-Antagonists↗