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PubMed1991

Myocardial preservation in neonatal lambs. Comparison of hypothermia with crystalloid and blood cardioplegia.

Low cardiac output after surgically induced myocardial ischemia is a major contributor to mortality and morbidity after operations for congenital heart defects, despite myocardial "protection" with the techniques of hypothermia and cardioplegia that have been effective in protecting mature myocardium. The purpose of this study was to investigate the effectiveness of topical cooling to 15 degrees C, crystalloid cardioplegia, and blood cardioplegia in protecting 28 isolated neonatal lamb hearts subjected to 2 hours of ischemia. Seven hearts were isolated and perfused in a similar manner with cooling to 15 degrees C but were then rewarmed without any ischemia to serve as a control group. All three groups (topical cooling, crystalloid cardioplegia, and blood cardioplegia) had recovery of systolic function (as measured by maximum developed pressure, maximum rate of pressure rise, peak developed pressure at a fixed volume, and peak rate of pressure rise at a fixed volume) equal to the control group; the exception was peak rate of pressure rise at a fixed volume in the blood cardioplegia group, in which recovery was worse than in the control group. No differences among three ischemia groups or in comparison with the control group were found for measures of diastolic function (ventricular diastolic pressure at a fixed volume or stiffness constant kA). Systolic function declined in all groups (including control) from baseline to the end of the experiment. These findings suggest that hypothermia exerted the dominant protective effect in these normal neonatal lamb hearts and there was no added protection from either crystalloid or blood cardioplegia.

Animals↗
PubMed1990

Physiological differences between strong and weak frog neuromuscular junctions: a study involving tetanic and posttetanic potentiation.

This paper describes the extent of release and terminal variability among normal frog sartorius neuromuscular junctions and seeks physiological correlates for these differences. Terminal length varied over approximately a 10-fold range, quantal content and release per unit terminal length ("release efficacy") over much larger ranges. For purposes of comparison of different junctions, release efficacy in a Ringer's containing 0.25 mM Ca2+ was determined in all cases. In a Ringer's containing 0.1 mM Ca2+, tetanic stimulation causes a buildup of evoked release and of miniature endplate potential (mEPP) frequency. The mEPP frequency at the end of the tetanus is proportional to the evoked release level. Following the tetanus, the mEPP frequency declines in a multiexponential fashion, with the 2 longest decay phases, representing augmentation and posttetanic potentiation (PTP), both having time constants that are positively linearly correlated with the synaptic release efficacy. Longer or higher-frequency tetanic stimulation resulted in a longer time course of decay of mEPP frequency. In a Ca2(+)-free/EGTA Ringer's, tetanic stimulation causes no evoked release, but does lead to an increased mEPP frequency, presumably due to a buildup of free Ca2+ displaced from internal stores by the Na+ influx. Following the tetanus, the mEPP frequency declines to resting level with a time constant that is essentially the same for all junctions, regardless of their release efficacy in Ca2(+)-containing Ringer's. These findings indicate that stronger terminals have a greater influx of Ca2+ per unit length during action potential invasion, but that in the absence of external Ca2+, tetanic stimulation results in comparable release of Ca2+ from internal stores in all terminals and comparable accumulation of Ca2+ in some large compartment, the subsequent emptying of which determines the time course of PTP.

Animals↗
PubMed1990

[The relaxation of the coronary artery smooth muscles under the action of a high-potassium solution].

The relaxation of the smooth muscle circular strips of cattle coronary arteries was studied under the increasing [K+]O using a modified sucrose gap technique. The relaxation occurred in three cases: 1) when the elevated [K+]O was moderate (up to 40 mmol/l); 2) at the beginning of high [K+]O action (60-160 mmol/l); 3) when the [K+]O was elevated (up to 160 mmol/l) under the conditions of a calcium current blockade. In each case the relaxation was connected with slow depolarization of the smooth muscle cells membrane and depressed by beta-adrenergic blocking agent propranolol (10(-5) mol/l). The relaxant action of the high-potassium solution on the coronary smooth muscle is actualized via the noradrenaline release from intramural nerve endings.

Animals↗
PubMed1990

[Delta sleep-inducing peptide as a modulator of mediators acting on the heart].

Experiments on 51 isolated rabbit hearts have documented, that delta sleep-inducing peptide (6 X 10(-6) M/l) has a modulating effect on the mediators influencing the heart. This peptide enhances negative chronotropic effect of acetylcholine (1 X 10(-6) M/l) and decreases positive chronotropic effect of noradrenaline (1 X 10(-6) M/l). Such effect may be one of mechanisms of changes in the extracardiac regulation on the heart influenced by this peptide.

Acetylcholine↗
PubMed1981

The effect of longitudinal tension on the amplitude of the contraction rhythm of plasmodial strands of Physarum polycephalum.

Plasmodial strands of Physarum polycephalum exhibit a characteristic contraction rhythm. The amplitude of the isotonic tension increased linearly with the cube root of relative stress. The period of the isometric tension increased linearly with the amplitude of the oscillation, but stayed constant above a critical value. The above empirical formulae were found applicable for all temperatures employed, 9 to 28 degrees C, but different temperature coefficients were observed below and above 15 to 16 degrees C.

Cytoplasm↗
PubMed1995

[Effects of resuscitation with hypertonic sodium lactate dextran 70 on cardiac function in severely burned dogs].

This comparative study was performed to evaluate the effects of resuscitation of burn shock with hypertonic sodium lactate dextran 70(HLD solution: Na+250 mmol/L and 6% dextran 70) and lactate Ringer' solution on cardiac function, lipid peroxide and SOD activity of heart tissue. Dogs with 35% TBSA third degree burns received, one hour postburn, either HLD resuscitation (HLD group, n = 6) in the amount of 19.6 ml.kg-1/g hours, followed by LR 6 ml.kg-1/% TBSA, or LR resuscitation (LR group, n = 6) in the amount of 8 ml.kg-1/% TBSA LR solution. The results of this experiment showed that cardiac index (CI) of HLD group was much higher than that of LR group at 4, 8, 12, 24 hours postburn. The dp/dt max and-dp/dt max of HLD group were much higher than that of LR group at 12.24 hours postburn. Level of MDA in heart tissue of HLD group (1.74 +/- 0.28 10 mol/g heart tissue) was much lower than of LR group (3.23 +/- 0.56 10 mol/g heart tissue) at 24 hours postburn (P < 0.01). Meanwhile, SOD activity in heart tissue of HLD group (157.49 +/- 32.23 u/mg heart tissue) was much higher than that of LR group (46.88 +/- 16.28 u/mg heart tissue) (P < 0.01). These results suggested that HLD resuscitation might be beneficial in improving postburn cardiac function and attenuating postburn oxidant-induced lipid peroxidation in heart tissue not only by its "oxygen scavenger" effect, but also by its elevation of SOD activity of heart tissue.

Animals↗
PubMed1987

Mechanics of tonus fibers of frog muscle.

Contractions with two phases of relaxation are induced by brief strong stimulation in some frog muscles. The first phase with rapid relaxation is produced by the twitch fibers; the second phase, which is very slow and is only present after strong stimulation, represents the relaxation of the tonus fibers. At moderate loads, half time of isotonic relaxation of these fibers is as long as 30 min at 2 degrees C, but the rate varies with the load and depends on the condition of the frogs. With regard to the rate of relaxation, the tonus fibers resemble molluscan catch muscles. In tonus fibers, rapid isotonic and isometric relaxation can be induced by a small extension; shortening opposes this effect. These responses are like the length responses previously found in various types of striated muscle. They go in the same direction as the well-known metabolic effects of length changes (Fenn effect). After a large extension by an increase in load there is no active shortening when the load is returned to the previous value. This and other observations show that the slowness of relaxation is not due to sustained activity, but is determined by the strength of the contractile bonds formed during contraction. Because activity during relaxation is very low, it is unlikely that length responses are caused by a modification of the cross-bridge cycle. It is suggested that length changes act through a mechanism that is separate from that initiating contraction, but alters the speed of relaxation by making the cross bridges weaker or stronger.

Animals↗
PubMed1977

Oscillating contractions in protoplasmic strands of Physarum: simultaneous tensiometry of longitudinal and radial rhythms, periodicity analysis and temperature dependence.

1. The construction of a 'twin-tension transducer' allows the simultaneous measurement of the same or different contraction rhythms at any selected sites of living plasmodia of Physarum polycephalum. This method has been used to analyse the relation of longitudinal and radial contraction activity within migrating plasmodia and plasmodial veins, under isometric as well as under isotonic conditions of measurement. 2. A periodicity analysis of the oscillating contraction rhythms revealed average period values for the longitudinal contraction cycle of 2-1 min and for the radial contraction cycle of 1-3 min at a temperature of 22 degrees C. 3. The periods of longitudinal contraction depend on the environment of the strands. The mean value under submerged conditions was 2-9 min. 4. The temperature dependences for both longitudinal and radial contraction cycles were determined to provide reliable values for the normal reaction range of the contractile system (cytoplasmic actomyosin). The values for radial contraction activity are 2-0 min at 16 degrees C, 1-5 min at 20 degrees C, and 1-2 min at 24 degrees C. The range between 16 degrees and 24 degrees C can be regarded as physiological. 5. The possibility is discussed that only one 'genuine' contraction frequency of cytoplasmic actomyosin exists in Physarum.

Cytoplasm↗