Modulation of myocardial economy and efficiency in mammalian failing and non-failing myocardium by calcium channel activation and beta-adrenergic stimulation

OBJECTIVE: We investigated the energy-metabolic consequences of positive inotropic stimulation by the calcium channel activator, BAY K 8644, in comparison with isoprenaline, focussing both on the economy of force development and the efficiency of external work. METHODS: In the first instance, heat liberation was measured in isometrically contracting right ventricular papillary muscles from guinea pigs by means of antimony-bismuth thermopiles; in the second instance, external work and myocardial oxygen consumption were analyzed in isolated failing and non-failing working rat hearts. RESULTS: In the guinea pig muscle strip preparations BAY K 8644 (10(-5) M) and isoprenaline (10(-8 M) increased peak developed force from 13.7 +/- 2.7 to 37.6 +/- 14.9 mN/mm2 and from 13.6 +/- 5.2 to 38.8 +/- 3.3 mN/mm2, respectively (P < 0.01). Stress-time integral was increased from 10.3 +/- 3.0 to 34.7 +/- 19.2 mN.s/mm2 by BAY K 8644 and from 9.5 +/- 2.4 to 23.0 +/- 1.6 mN.s/mm2 by isoprenaline. Whereas a significant decrease in the ratio between stress-time integral and initial heat (integral of Pdt/IH) (i.e., economy contraction) was observed for isoprenaline (5.26 +/- 1.91 before and 3.11 +/- 0.72 N.m.s.J-1 after treatment (P < 0.01), BAY K 8644 did not significantly alter this index (5.26 +/- 2.39 before and 6.22 +/- 2.63 N.m.s.J-1 after treatment). Similar results were obtained for the ratio between stress-time integral and tension-dependent heat. Significantly more calcium ions were required for equieffective activation of the contractile proteins with isoprenaline as compared to BAY K 8644. In working preparations of sham-operated and infarcted rat hearts, the increase in myocardial oxygen consumption per minute (delta MVO2) for a given increase in external work per minute (delta P) was significantly higher with isoprenaline than with equipotent concentrations of BAY K 8644 or high calcium. CONCLUSIONS: Inotropic mycardial stimulation by BAY K 8644 is associated with higher economy and efficiency than stimulation by isoprenaline when analyzed both by heat measurements in isometric preparations and by myocardial oxygen consumption in working heart preparations.     

Potent stimulation of myofilament force and ATPase activity of skeletal muscle by eudistomin M, a novel Ca(++)-sensitizing agent from a Caribbean tunicate

In the course of our survey of biologically active compounds from natural sources, eudistomins were isolated from a Caribbean tunicate Eudistoma olivaceum. In the present experiments, eudistomin M (Eud-M, > 10(-5) M) caused a concentration-dependent increase in the contractile response of skinned fibers from guinea pig skeletal psoas muscles to Ca++. The superprecipitation and ATPase activity of myosin B from fast skeletal muscles of rabbit back and leg were potentiated by this compound (> 10(-5) M) in a concentration-dependent manner. In skinned fibers, superprecipitation and the ATPase activity of myosin B, Eud-M shifted the concentration-response curve for Ca++ to the upper direction. Ca(++)-, K(+)-EDTA- or Mg(++)-ATPase was not affected by Eud-M. This compound had no effect on the ATPase activity of actomyosin reconstituted from actin and myosin in the presence or absence of troponin. However, the ATPase activity of actin-myosin-troponin-tropomyosin reconstituted system was increased significantly by Eud-M. These results suggest that Eud-M increases the Ca++ sensitivity of the contractile apparatus in skeletal muscles at least partially mediated through troponin-tropomyosin system and thus enhances the ATPase activity of myosin B and the contractile force of myofilament.     

Study of molecular mechanisms of muscle contraction using polarization fluorometry

The review summarizes results of studies on the conformational changes in contractile proteins during muscle contraction. The studies were carried out by polarized fluorescence technique in the UV and visible light. The revealed were alterations of actin and myosin in muscle fiber, taking place at various stages of contractile cycle. Transition from a weak binding state of actomyosin to a strong one was accompanied by F-actin subunit rearrangements, with C- and N-terminals moving relative to the core of thin filament. Myosin light chains and 20-kDa domain of myosin head moved in the same direction as C- and N-terminal regions of actin. The flexibility of actin filaments increased, whereas that of C- and N-terminal regions decreased sharply. Actin-myosin interaction changed dramatically tropomyosin flexibility and caused displacement of the protein relative to C- and N-terminals of actin. Actin structure "freezing" by glutaraldehyde or phalloidin, actin cleavage by subtilisin, as well as actin alteration in denervational atrophy inhibited markedly the intramolecular movement and isometric tension of muscle contraction. Besides, troponin-, caldesmon-, calponin-, and myosin-systems, regulating muscle contraction, modified actomyosin rearrangements in a Ca(2+)-dependent manner. The role of the movement of polypeptide chains in contractile proteins during muscle contraction is discussed.     

Effect of rapid digitalization on the left-ventricular myocardial function according to the echocardiographic data

The article deals with the data of echocardiographic examination of 61 patients (37 with rheumatic heart disease and 17 with atherosclerotic cardiosclerosis) subjected to rapid stage-by-stage digitalization by intravenous administration of various rapidly acting glycosides. In 10 patients with ischemic heart disease echocardiography was performed following a single strophanthin injection. Decrease in the volumes of the left ventricle and increase in the indices of central hemodynamics were noted as a result of rapid stage-by-stage saturation with strophanthin. The maximum inotropic effect of strophanthin does not coincide in time with the maximum chronotropic effect. The increase in the stroke volume noted in maximum deceleration of cardiac contractions is probably realized due to the Frank-Starling mechanism. Strophanthin increases the rate of myocardial contractions without changing the duration of the systole. The rate of diastolic relaxation grows, the phase of rapid filling becomes shorter and the phase of slow filling longer, which creates favourable conditions for the next contraction.     

Persistent enhancement of potassium-induced responses of the rat vas deferens by desipramine

The effect of desipramine on the cumulative dose-response curves of noradrenaline and potassium (K+) was examined on the isolated rat vas deferens. An exposure of 10 min to 10(-7) M desipramine caused a leftward shift and an increase in the maximum response of cumulative dose-response curves of noradrenaline. Desipramine (10(-7) M), in contact with the tissue for 10 min, enhanced responses to cumulative additions of K+ without causing a consistent change in threshold concentrations. Wash-out of desipramine resulted in a rapid loss of enhanced maximum response to noradrenaline while the maximum response to K+ did not show any decrease for up to 120 min after wash-out of drug. One possible explanation for the persistent enhancement of K+-induced responses may be that desipramine causes postjuntional changes which selectively influence contractile responses of this tissue to K+.     

Effects of renovascular hypertension on myocardial protein patterns: analysis by computer-assisted two-dimensional gel electrophoresis

Hypertensive heart disease caused by renovascular hypertension reflects the response of the heart to an increased afterload and neurohormonal stimulation. We hypothesized that in this condition the composition of the myocardial proteins of rats was altered. To identify yet unknown quantitative and qualitative differences in myocardial proteins in renovascular hypertensive heart disease, we analyzed protein patterns by computer-assisted two-dimensional polyacrylamide large gel electrophoresis. Renovascular hypertension was induced by placing a silver clip on the left renal artery in 9-week-old rat siblings. Sham-operated animals served as controls. Systolic blood pressure (197 +/- 19 mm Hg) and heart/body weight ratios (0.36 +/- 0.04%) were significantly increased in the hypertensive animals. Twenty protein patterns from the left ventricle of five hypertensive and five control rats were compared. The molecular mass and isoelectric point (pI) of proteins spots ranging from 13 to 100 kDa and from 4.5 to 8.5, respectively, were determined using marker proteins. In total, 761 +/- 88 protein spots were resolved in all twenty gels. For the quantitative data analysis a univariate (Mann-Whitney test) as well as a multivariate statistical approach (correspondence analysis) were applied. Only one myocardial protein spot (molecular mass = 41.3 kDa; pI = 6.3) was decreased by more than twofold (p < 0.05) in renovascular hypertension. The vast majority of spots did not indicate a significant alteration of intensity. Left ventricular hypertrophy in early renovascular hypertension induces a form of myocardial hypertrophy that conserves the naturally occurring protein expression pattern.     

Dynamic cardiac compression improves contractile efficiency of the heart

The effect of dynamic cardiac compression on left ventricular contractile efficiency was assessed in terms of the pressure-volume relationship and myocardial oxygen consumption. In 11 excised cross-circulated dog hearts, the ventricle was directly compressed during systole (dynamic cardiac compression). Measurements for pressure-volume area (a measure of total mechanical energy), external work, and myocardial oxygen consumption were done before and during dynamic cardiac compression. Dynamic cardiac compression increased pressure-volume area by 28% +/- 17% (mean plus or minus the standard deviation) and external work by 24% +/- 20% (p = 0.0000185 and 0.0000212, respectively) at given end-diastolic and stroke volumes without affecting myocardial oxygen consumption. As a result, the oxygen cost of pressure-volume area, that is, the slope of the myocardial oxygen consumption-pressure-volume area relationship, significantly decreased by 16% +/- 13% (p = 0.0000135) whereas the pressure-volume area-independent myocardial oxygen consumption was unchanged. Then, contractile efficiency, that is, the reciprocal of the slope of the myocardial oxygen consumption-pressure-volume area relationship in joules significantly improved from 45% +/- 8% to 53% +/- 13% (p = 0.0000437). When the native myocardial oxygen consumption-pressure-volume area relationship was assessed by subtracting the dynamic cardiac compression pressure applied to the heart, the slope of the myocardial oxygen comsumption-pressure-volume area relationship returned to the control level. This indicates that the contractile efficiency of the native heart was not affected by dynamic cardiac compression. We conclude that dynamic cardiac compression enhances left ventricular pump function by improving the contractile efficiency of the overall heart leaving the energetics of the native heart unchanged.     

Attenuation by creatine of myocardial metabolic stress in Brattleboro rats caused by chronic inhibition of nitric oxide synthase

1. The present experiment was undertaken to investigate: (a) the effect of nitric oxide synthase (NOS) inhibition, mediated by oral supplementation of the NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), on measures of myocardial energy metabolism and function: (b) the effect of oral creatine supplementation on these variables, in the absence and presence of L-NAME. 2. In one series of experiments, 4 weeks oral administration of L-NAME (0.05 mg ml-1 day-1 in the drinking water) to Brattleboro rats caused significant reductions in myocardial ATP, creatine, and total creatine concentrations and an accumulation of tissue lactate when compared with control animals. Administration of creatine (0.63 mg ml-1 day-1 in the drinking water) for 4 weeks elevated myocardial creatine and total creatine concentrations and reduced lactate accumulation, but did not significantly affect ATP or phosphocreatine (PCr). Concurrent treatment with creatine and L-NAME prevented the reduction in creatine and total creatine concentrations, and significantly attenuated the accumulation of lactate and the reduction in ATP seen with L-NAME alone. 3. In a second series of experiments, 4 weeks treatment with L-NAME and creatine plus L-NAME increased mean arterial blood pressure in conscious Brattleboro rats. Hearts isolated from these animals showed decreased coronary flow and left ventricular developed pressure (LVDP), and total mechanical performance. Treatment with creatine alone had no measurable effect on either mean arterial blood pressure or coronary flow in isolated hearts. However, there was an increase in LVDP, but not in total mechanical performance, because there was a bradycardia. 4. These results indicate that creatine supplementation can attenuate the metabolic stress associated with L-NAME administration and that this effect occurs as a consequence of the action of creatine on myocardial energy metabolism.     

Acute cardiac ischemia and reperfusion: contractility, relaxation, and glycolysis

The mechanical and metabolic effects of 3 min of complete global ischemia and 25 min of reperfusion were studied in the isolated rat heart. The decrease in contracile function was biphasic; a rapid 50% decline occurred in the first 10 s of ischemia, after which contractile function transiently stabilized and then fell at a slower rate. During reperfusion, recovery of relaxation was impaired relative to recovery of contractile function. A second period of ischemia and reflow produced changes in contractility, relaxation, and lactate production virtually identical to the initial one. In the absence of glycolytic blockade, tissue lactate accumulation developed, no contracture occurred, the pacing threshold did not increase, and reperfusion after 3 min of ischemia resulted in complete recovery of contractile function. Glycolytic blockade with 0.1 mM iodoacetate (IAA) prevented ischemic lactate production, accelerated the fall in contractility, caused irreversible contracture after 30 s of ischemia, an irreversible increase in pacing threshold within 3 min of ischemia, and poor recovery of contractile function with reperfusion. Thus during the first 3 min of severe ischemia, glycolysis exerted a net beneficial effect on myocardial function despite significant tissue lactate accumulation.     

Role of sodium ions in the protective action of nucleotides and their hydrolytic products in calcium paradox

Nucleotides were examined for their effects on the development of calcium paradox in the isolated rat heart. The protective action of nucleotides was found to be unassociated with the structure of their nitrogen base. The products of extracellular hydrolysis, such as ribose (deoxyribose), uridine or adenosine at a concentration of 100 microM caused no less protective effects than nucleotides. In calcium paradox, the protective action of adenosine was not suppressed by theophylline, but sensitive to dipyridamole and transmembrane Na gradient values. Nucleotides and their hydrolytic products were demonstrated to exert a positive myocardial effect not only at the physiological (140 microM), but increased Na ion concentrations. The high extracellular Na concentration-induced potentiation of the protective action of nucleotides or their hydrolytic products was blocked by strophanthin. It is suggested that the high Na gradient can increase the protective action of nucleotides and their hydrolytic products due to decreased Na-Ca metabolism and to the altered metabolism of nucleotide hydrolytic products.     

Effect of cardiac desympathization, stimulation of the central adrenergic structures and blockade of beta-adrenergic receptors on cardiotonic and cardiotoxic effect of cardiac glycosides

The object of study were rabbits who had been subjected to ligation of 3 or 4 large branches of the left descending coronary artery 14-20 days before the experiment. In experiments with surgical desympathization of the heart it was established that the inotropic effect of cardiac glycosides did not depend on the concentration of catecholamines in the myocardium. In stimulation of adrenergic structures of the posterior hypothalamus attended with an increase in sympathetic innervation of the cardiovascular system the cardiotoxic threshold of cardiac glycosides was considerably reduced. Propranolol (Inderal) administered in a dose which blocks the beta-adrenergic apparatus of the heart prevents the development of the positive inotropic effect of therapeutic doses of strophanthin K on a hypodynamic left ventricular myocardium.     

Lysophosphatidylcholine potentiates vascular contractile responses by enhancing vasoconstrictor-induced increase in cytosolic free Ca2+ in rat aorta

We investigated the effects of palmitoyl-L-alpha-lysophosphatidylcholine on the contractile responses of the endothelium-denuded rat aorta to high K+, noradrenaline, UK14,304 (5-bromo-6-[2-imidazolin-2-ylamino]-quinoxaline) (a selective alpha2 adrenoceptor agonist) and phorbol 12-myristate 13-acetate (PMA). Lysophosphatidylcholine at concentrations from 10(-6) M to 10(-4) M did not contract aortic strips. However, lysophosphatidylcholine strongly potentiated the UK14,304-induced contraction. High K+ - and PMA-induced contractions were also potentiated. In contrast, the noradrenaline-induced contraction was only slightly potentiated by 10(-5) M lysophosphatidylcholine. In fura PE-3-loaded aortic strips, lysophosphatidylcholine (10(-5) M) markedly augmented the increase in both cytosolic free Ca2+ ([Ca2+]i) and contractile tension induced by UK14,304, high K+ and PMA. Nicardipine (10(-7) M) and 10(-6) M Ro-31-8220 (?1-[3-(amidinothio)propyl-1H-indoyl-3-yl]-3-(1-methyl-1H-++ +indoyl-3-yl)-maleimide-methane sulfate) strongly inhibited the increase in [Ca2+]i and contractile tension induced by UK14,304 and in the presence of these inhibitors, the enhancing effects of lysophosphatidylcholine were attenuated. However, the enhancing effect on high K+ -induced contraction was not affected by Ro-31-8220. These results suggest that lysophosphatidylcholine may cause an augmentation of the increase in [Ca2+]i induced by UK14,304 which response is depend on protein kinase C activation and in this way potentiate contractile responses in the rat aorta. Protein kinase C independent mechanisms may also be involved in the enhancing effect of lysophosphatidylcholine on smooth muscle contraction.     

Inhibition of myocardial L- and T-type Ca2+ currents by efonidipine: possible mechanism for its chronotropic effect

Effects of efonidipine, a dihydropyridine phosphonate Ca2+ channel antagonist, on the guinea-pig heart were compared with those of nifedipine. In the sino-atrial node, 1 microM efonidipine produced increase in cycle length accompanied by prolongation of the phase 4 depolarization which was not prominent with 0.1 microM nifedipine. In ventricular myocytes, both efonidipine and nifedipine produced inhibition of the L-type Ca2+ current, nifedipine being tenfold more potent than efonidipine. Efonidipine also inhibited the T-type Ca2+ current at higher concentrations but nifedipine did not. Both Ca2+ channel antagonists had no or only a weak effect on K+ currents. In addition, 40 microM Ni2+, which selectively inhibited the T-type Ca2+ current, had no effect on myocardial Ca2+ transients and contractile force. In conclusion, efonidipine was shown to have inhibitory effects on both L- and T-type Ca2+ currents, which may contribute to its high negative chronotropic potency.     

Effects of sevoflurane or halothane on contractile responses of isolated canine basilar artery

Although volatile anesthetic is known as a cerebral vasodilator, its mechanism is not clear. The purpose of this study was to investigate effects of sevoflurane or halothane on contractions induced by high K+ and serotonin in the isolated canine basilar artery. Cylindrical segments of canine basilar artery were placed in Krebs solution oxygenated with 95% O2 and 5% CO2 at 37 degrees C. They were then constricted with cumulative administration of 10 to 60 mM KCl, or with 10(-9) to 10(-6) M serotonin and exposed to either sevoflurane or halothane at concentration of 1.0 and 2.0 MAC. Halothane and sevoflurane at concentration of 1.0 and 2.0 MAC decreased contractile responses evoked by KCl to a similar degree. The attenuation by either of the two anesthetics at concentration of 2.0 MAC were equivalent to the inhibitions by diltiazem 2 x 10(-7) M. Contractile responses to serotonin above 3 x 10(-7) M were depressed by halothane 1.0 MAC, but not by sevoflurane 1.0 MAC. Sevoflurane and halothane at concentration of 2.0 MAC decreased contractile responses evoked by serotonin at concentrations above 3 x 10(-8) M and 10(-8) M. Removal of the endothelium did not alter the response of the basilar artery contracted by serotonin to either anesthetic. These findings suggest that sevoflurane and halothane depress the voltage-dependent Ca2+ channels due to decreases of contractile responses to high K+. Our results also demonstrate that sevoflurane is a less potent vasodilator of the basilar artery contracted by serotonin than halothane.     

Assembly mechanism of Dictyostelium myosin II: regulation by K+, Mg2+, and actin filaments

Regulated assembly of myosin II in Dictyostelium discoideum amoebae partially controls the orderly formation of contractile structures during cytokinesis and cell migration. Kinetic and structural analyses show that Dictyostelium myosin II assembles by a sequential process of slow nucleation and controlled growth that differs in rate and mechanism from other conventional myosins. Nuclei form by an ordered progression from myosin monomers to parallel dimers to 0.43 microns long antiparallel tetramers. Lateral addition of dimers to bipolar tetramers completes the assembly of short (0.45 microns) blunt-ended thick filaments. Myosin heads are not staggered along the length of tapered thick filaments as in skeletal muscle, nor are bipolar minifilaments formed as in Acanthamoeba. The overall assembly reaction incorporating both nucleation and growth could be kinetically characterized by a second-order rate constant (kobs,N+G) of 1.85 x 10(4) M-1 s-1. Individual rate constants obtained for nucleation, kobs,N = 4.5 x 10(3) M-1 s-1, and growth, kobs,G = 2.5 x 10(4) M-1 s-1, showed Dictyostelium myosin II to be the slowest assembling myosin analyzed to date. Nucleation and growth stages were independently regulated by Mg2+, K+, and actin filaments. Increasing concentrations of K+ from 50 to 150 mM specifically inhibited lateral growth of dimers off nuclei. Intracellular concentrations of Mg2+ (1 mM) accelerated nucleation but maintained distinct nucleation and growth phase kinetics. Networks of actin filaments also accelerated the nucleation stage of assembly, mechanistically accounting for spontaneous formation of actomyosin contractile fibers via myosin assembly (Mahajan et al., 1989). The distinct assembly mechanism and regulation utilized by Dictyostelium myosin II demonstrates that myosins from smooth muscle, striated muscle, and two types of amoebae form unique thick filaments by different pathways.     

Erythropoietin modified the cardiac action of ouabain in chronically anaemic-uraemic rats

The results of the studies reported here demonstrate the cardiac non-haematopoietic effect of erythropoietin, providing a new physiological function of the hormone. We demonstrate that myocardium from rat with chronic renal failure (CRF) showed an abnormal response to ouabain associated with an inhibition of cardiac Na+/K+/ATPase activity and with a decrease in the high affinity 3H-ouabain binding sites. The extent to which both actions were improved with the recombinant human erythropoietin (rHuEpo) treatment suggests that the lack of the hormone is responsible for this phenomenon. The fact is that neither contractile nor enzymatic action of rHuEpo was accompanied with the improvement of the functional renal and haematologic parameters, indicating a primary effect on myocardial contractile function of rHuEpo, independent of the anaemic and uraemic state of the animal. The reason why erythropoietin is able to modulate directly the cardiac Na+/K+ pump makes it possible to conclude that the lack of erythropoietin in CRF may be at least in part responsible for the inhibition of cardiac enzymes, altering the contractile behaviour of the heart.     

Osmolyte-driven contraction of a random coil protein

The Stokes radius characteristics of reduced and carboxamidated ribonuclease A (RCAM RNase) were determined for transfer of this "random coil" protein from water to 1 M concentrations of the naturally occurring protecting osmolytes trimethylamine N-oxide, sarcosine, sucrose, and proline and the nonprotecting osmolyte urea. The denatured ensemble of RCAM RNase expands in urea and contracts in protecting osmolytes to extents proportional to the transfer Gibbs energy of the protein from water to osmolyte. This proportionality suggests that the sum of the transfer Gibbs energies of individual parts of the protein is responsible for the dimensional changes in the denatured ensemble. The dominant term in the transfer Gibbs energy of RCAM RNase from water to protecting osmolytes is the unfavorable interaction of the osmolyte with the peptide backbone, whereas the favorable interaction of urea with the backbone dominates in RCAM RNase transfer to urea. The side chains collectively favor transfer to the osmolytes, with some protecting osmolytes solubilizing hydrophobic side chains as well as urea does, a result suggesting there is nothing special about the ability of urea to solubilize hydrophobic groups. Protecting osmolytes stabilize proteins by raising the chemical potential of the denatured ensemble, and the uniform thermodynamic force acting on the peptide backbone causes the collateral effect of contracting the denatured ensemble. The contraction decreases the conformational entropy of the denatured state while increasing the density of hydrophobic groups, two effects that also contribute to the ability of protecting osmolytes to force proteins to fold.     

Regulation of adrenergic nerve-mediated contraction of canine pulmonary artery by K+ channels

The aim of the present study was to investigate the role of certain subtypes of K+ channels in nerve-evoked contractions of pulmonary artery in vitro. The lobar or segmental pulmonary arteries were dissected from dogs, cut into ring segments, and the contractile responses to electrical field stimulation (EFS) and noradrenaline were measured under isometric conditions. Addition of iberiotoxin, a big conductance Ca2+-activated K+ channel blocker, and apamin, a small conductance Ca2+-activated K+ channel blocker, did not change the resting tension but augmented the contractile responses to EFS, so that the electric stimulus frequency required to produce a half-maximal contraction (ES50) was decreased from 18.2+/-3.5 to 7.4+/-2.3 Hz (p<0.01) and from 16.8+/-2.2 to 11.4+/-2.0 Hz (p<0.05), respectively, whereas glibenclamide, an adenosine triphosphate (ATP)-sensitive K+ channel blocker, had no effect. In contrast, none of the K+ channel blockers altered the contractile response to noradrenaline. Incubation of tissues with iberiotoxin and apamin increased the release of 3H-noradrenaline evoked by EFS. We conclude that big conductance Ca2+-activated K+ channels and small conductance Ca2+-activated K+ channels may play a role in the regulation of adrenergic neurotransmission in the pulmonary artery, probably by inhibiting the exocytotic release of noradrenaline from the adrenergic nerve terminals.     

Predicting hemodialysis access failure with color flow Doppler ultrasound

Large surface-area burns in patients have been associated with a severe impairment in cardiac performance, as evidenced by a decline in cardiac output. The mechanisms responsible for this profound myocardial dysfunction are largely unknown. We investigated the effects of lymph isolated from the scalded hind limb of dogs on regional myocardial blood flow, coronary vascular reactivity, and contractile performance. Dogs were instrumented with ultrasonic dimension crystals in the myocardium supplied by the left anterior descending (LAD) and by the left circumflex (LCx) coronary arteries. After cannulating a hind limb lymphatic, lymph was infused directly into the LAD before and after a 10-second 100 degrees C hind limb scald. Scalding alone did not alter myocardial contractile performance in the LAD or LCx regions, coronary artery blood flow, or systemic hemodynamics. Interestingly, postburn lymph infused into the LAD resulted in a 38% decline in LAD zone segment shortening (p < 0.01 vs baseline) that lasted throughout the 5-hour observation period. In contrast, segment shortening in the (control) LCx region was unaffected by postburn lymph injections into the LAD. Regional myocardial blood flow (radiolabeled microspheres) in the LAD and LCx regions was unchanged after scald injury or intracoronary injection of postburn lymph. In addition, LAD coronary artery vascular reactivity to acetylcholine and nitroglycerin was also unaffected by the regional thermal injury or by injection of lymph into the LAD. These data suggest that a regional scald injury results in the production and release of a potent myocardial depressant factor(s) that produces a direct negative inotropic effect on the canine myocardium.     

Inhibition of thrombin-induced contractile responses by protein kinase inhibitors in porcine pulmonary arteries

The clotting enzyme thrombin is known to cause receptor-mediated contractile effects in isolated blood vessels. In the present studies the influence of protein kinase inhibitors on the contractile response of porcine pulmonary arteries to thrombin (3 U/ml) was investigated. Endothelium-denuded rings (2-3 mm) from small arteries were placed in organ baths for isometric tension recording. The vessels were preincubated for 30 min with the inhibitors before inducing contractions. In the presence of the protein kinase C (PKC)-inhibitors staurosporine, BIM I (bisindolyl-maleimide I), chelerythrine and Ro 31-8220 (1 microM each), the contractile responses to the PKC activator phorbol 12,13-dibutyrate (PDBu; 50 nM) were diminished by 70-100%. However, for inhibition of thrombin-induced contractions generally higher concentrations of the inhibitors were required. Only staurosporine at 1 microM inhibited the thrombin effect by about 75%. The tyrosine kinase inhibitor erbstatin (30 microM) did not significantly alter the thrombin effect, whereas genistein at 10 microM caused a significant inhibition of contractile responses to both thrombin and PGF2alpha. At 100 microM genistein also inhibited the contractile effects of PdBu and KCl. These studies suggest that activation of both PKC and non-receptor tyrosine kinases seems to be involved in the signal transduction pathways of thrombin-induced contractile effects in isolated vessels.