Contractile function and myofibrillar ATPase activity in the exercise-trained dog heart

1977 ◽  
Vol 43 (6) ◽  
pp. 977-982 ◽  
Author(s):  
R. T. Dowell ◽  
H. L. Stone ◽  
L. A. Sordahl ◽  
G. K. Asimakis
Keyword(s):  
Heart Rate ◽  
Exercise Training ◽  
Atpase Activity ◽  
Contractile Function ◽  
Left Ventricular Pressure ◽  
Left Ventricular ◽  
Submaximal Exercise ◽  
Treadmill Running ◽  
Myofibrillar Atpase ◽  
Myofibrillar Atpase Activity

Myocardial contractility and the enzymatic (ATPase) activity of cardiac contractile proteins were examined after exercise training using the chronically instrumented, unanesthetized dog as an experimental model. Before training, heart rate and the maximum rate of left ventricular pressure development (max dP/dt) were measured at rest and during submaximal exercise. Animals were then subjected to an 8- to 10-wk treadmill running program. Training was verified by the establishment of a 10- to 20-beat/min reduction in heart rate during submaximal exercise. After training max dP/dt was within normal limits at rest, but significantly elevated during submaximal exercise. When max dP/dt was plotted as a function of heart rate, either with the animal standing quietly on the treadmill or during submaximal exercise, a marked elevation in max dP/dt at any given heart rate was observed following training. Myofibrillar protein yield and ATPase activity values were nearly identical in left ventricles from exercise-trained and sedentary control dogs. Although exercise training by treadmill running improved contractile function in the unanesthetized dog myocardium, this response does not appear to involve alterations in myofibrillar ATPase activity.

Nutritional modification of rat heart postnatal development

1984 ◽  
Vol 246 (3) ◽  
pp. H332-H338 ◽  
Author(s):  
R. T. Dowell
Keyword(s):  
Atpase Activity ◽  
Postnatal Development ◽  
Contractile Function ◽  
Left Ventricular ◽  
Activity Level ◽  
Myofibrillar Atpase ◽  
Fast Growing ◽  
Growing Rats ◽  
Myofibrillar Atpase Activity ◽  
Slow Growing

Postnatal development of the mammalian myocardium encompasses increases in cellularity, energy producing and energy utilizing systems, and concurrent augmentation of heart contractile performance. The present study disrupted normal developmental sequences by adjusting the number of newborn rats per litter at 4 days postbirth. Fast-growing (4 rats/litter), normal (8 rats/litter), or slow-growing (16 rats/litter) animals were studied when 21 days old. Left ventricular cellularity (total DNA) increased as a function of the nutritionally modified growth of the heart, having values of 562 +/- 27, 625 +/- 33, and 791 +/- 20 (SE) micrograms in 16, 8, and 4 rats/litter groups, respectively. Low levels of systolic pressure (55 + 5 mmHg) and rate of pressure development (dP/dt, 2,670 +/- 130 mmHg/s) were noted in the slow-growing rats. Growth-related augmentation of pressure and dP/dt occurred such that adult levels (104 +/- 4 mmHg; 5,810 +/- 290 mmHg/s) were observed in 21-day-old, fast-growing rats. An enzymatic marker for aerobic metabolism (malate dehydrogenase) indicated mitochondrial accumulation in excess of ventricular tissue, thereby establishing progressive increases in aerobic capacity. Myofibrillar ATPase activity was not significantly different among all groups. Thus heart contractile function during nutritionally induced changes in postnatal development is augmented in proportion to increases in heart DNA content. A positive relationship also exists between dP/dt and number of mitochondria; however, enhanced contractile function is achieved independently of myofibrillar ATPase activity level.

Cardiac vagal modulation of heart rate during prolonged submaximal exercise in animals with healed myocardial infarctions: effects of training

2006 ◽  
Vol 290 (4) ◽  
pp. H1680-H1685 ◽  
Author(s):  
Monica Kukielka ◽  
Douglas R. Seals ◽  
George E. Billman
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Exercise Training ◽  
Submaximal Exercise ◽  
Treadmill Running ◽  
Myocardial Infarctions ◽  
Vagal Activity ◽  
Long Duration ◽  
Exercise Treadmill ◽  
Exercise Induced

The present study investigated the effects of long-duration exercise on heart rate variability [as a marker of cardiac vagal tone (VT)]. Heart rate variability (time series analysis) was measured in mongrel dogs ( n = 24) with healed myocardial infarctions during 1 h of submaximal exercise (treadmill running at 6.4 km/h at 10% grade). Long-duration exercise provoked a significant (ANOVA, all P < 0.01, means ± SD) increase in heart rate (1st min, 165.3 ± 15.6 vs. last min, 197.5 ± 21.5 beats/min) and significant reductions in high frequency (0.24 to 1.04 Hz) power (VT: 1st min, 3.7 ± 1.5 vs. last min, 1.0 ± 0.9 ln ms2), R-R interval range (1st min, 107.9 ± 38.3 vs. last min, 28.8 ± 13.2 ms), and R-R interval SD (1st min, 24.3 ± 7.7 vs. last min 6.3 ± 1.7 ms). Because endurance exercise training can increase cardiac vagal regulation, the studies were repeated after either a 10-wk exercise training ( n = 9) or a 10-wk sedentary period ( n = 7). After training was completed, long-duration exercise elicited smaller increases in heart rate (pretraining: 1st min, 156.0 ± 13.8 vs. last min, 189.6 ± 21.9 beats/min; and posttraining: 1st min, 149.8 ± 14.6 vs. last min, 172.7 ± 8.8 beats/min) and smaller reductions in heart rate variability (e.g., VT, pretraining: 1st min, 4.2 ± 1.7 vs. last min, 0.9 ± 1.1 ln ms2; and posttraining: 1st min, 4.8 ± 1.1 vs. last min, 2.0 ± 0.6 ln ms2). The response to long-duration exercise did not change in the sedentary animals. Thus the heart rate increase that accompanies long-duration exercise results, at least in part, from reductions in cardiac vagal regulation. Furthermore, exercise training attenuated these exercise-induced reductions in heart rate variability, suggesting maintenance of a higher cardiac vagal activity during exercise in the trained state.

Isoform-independent heart rate-related variation in cardiac myofibrillar Ca(2+)-activated Mg(2+)-ATPase activity

1996 ◽  
Vol 270 (5) ◽  
pp. C1271-C1276 ◽  
Author(s):  
W. Rouslin ◽  
C. W. Broge
Keyword(s):  
Heart Rate ◽  
Beef Cattle ◽  
Atpase Activity ◽  
Specific Activity ◽  
Myosin Atpase ◽  
Curvilinear Relationship ◽  
Mitochondrial Atpase ◽  
Myofibrillar Atpase ◽  
Cardiac Myosin ◽  
Myofibrillar Atpase Activity

In the present study, we compared the activities of the cardiac myofibrillar Ca(2+)-activated Mg(2+)-ATPase and the content of cardiac muscle mitochondrial ATPase inhibitor protein (IF1) of several mammalian species covering broad ranges of body mass and heart rate, i.e., from beef cattle to mouse. The cardiac myofibrillar ATPase from each species was assayed over a range of pCa values at pH 7.4. While the cardiac myofibrillar ATPase from all species examined showed essentially identical Ca2+ concentration dependencies with the ATPase in each species activating steeply between pCa 6.5 and 5.5, the maximal ATPase specific activity reached varied considerably from species to species, and this variation was largely independent of the predominant cardiac myosin ATPase isoform present. Thus, while adult beef cattle, pig, dog, and rabbit all contain predominantly the slow cardiac myosin ATPase isoform the cardiac myofibrillar ATPase specific activities of these four species varied over approximately a fourfold range. Moreover, there was a fairly smooth curvilinear relationship between maximum Ca(2+)-activated myofibrillar ATPase activity and median conscious heart rate for the slow cardiac myosin ATPase-possessing species examined. This smooth continuum also extended to include two species possessing the fast cardiac myosin ATPase isoform, rat and mouse. This relationship between myofibrillar ATPase activity and heart rate that appears to be applicable to a broad range of species suggests that the myofibrillar ATPase is specifically modeled or fine-tuned to the kinetic (heart rate) demand of each species and, within slow and fast heart rate ranges, is essentially independent of myosin ATPase isoform per se. Only hearts containing predominantly the slow myosin ATPase isoform contained functional levels of IF1. Finally, while it has been reported that the ratio of myosin Ca(2+)-ATPase to actomyosin Mg(2+)-ATPase activity is a good index of the percent of the fast myosin ATPase in rabbit myofibrillar preparations, we found that this relationship may be applicable to only some species.

Relation of glycosylated hemoglobin to in vivo cardiac function in response to dobutamine in spontaneously diabetic BB Wor rats

1994 ◽  
Vol 72 (7) ◽  
pp. 722-727 ◽  
Author(s):  
Tom L. Broderick ◽  
Stephen J. Kopp ◽  
June T. Daar ◽  
Fred D. Romano ◽  
Dennis J. Paulson
Keyword(s):  
Heart Rate ◽  
Cardiac Function ◽  
Metabolic Control ◽  
Contractile Function ◽  
Glycosylated Hemoglobin ◽  
Left Ventricular Pressure ◽  
Left Ventricular ◽  
Insulin Dependent ◽  
Myocardial Contractile

The contribution of metabolic control to in vivo myocardial contractile function in response to β1-adrenergic stimulation was determined in the spontaneously diabetic BB Wor rat. The study involved a group of insulin-dependent BB Wor rats showing marked variations in metabolic control, assessed by the level of glycosylated hemoglobin (gHb). These diabetic BB rats were divided into moderate and severe (%gHb > 14) diabetic groups. A group of Wistar rats and diabetes-resistant BB Wor rats served as controls. In vivo myocardial contractile function was measured under basal conditions and after i.v. dobutamine infusions in anesthetized rats, using a catheter-tip pressure transducer inserted into the left ventricle. No dramatic differences in heart rate with dobutamine stimulation were observed between the moderate, severe diabetic, and diabetes-resistant groups. However, heart rate was lower in Wistar control rats compared with these groups. Systolic left ventricular pressure was depressed in severe diabetic rats compared with Wistar controls. In addition, positive dP/dt was significantly less in the severe diabetic group at the highest doses of stimulation, whereas negative dP/dt was depressed under basal conditions and remained so with increasing doses of dobutamine. In the diabetic group maximal systolic left ventricular pressure, rate–pressure product, and negative dP/dt responses to dobutamine were all inversely correlated with gHb. These results indicate that changes in metabolic control of the insulin-dependent BB diabetic rat can contribute to a depressed myocardial contractile function.Key words: glycosylated hemoglobin, cardiac function, dobutamine, BB rat.

Effect of endurance exercise training on heart rate onset and heart rate recovery responses to submaximal exercise in animals susceptible to ventricular fibrillation

2007 ◽  
Vol 102 (1) ◽  
pp. 231-240 ◽  
Author(s):  
George E. Billman ◽  
Monica Kukielka
Keyword(s):  
Heart Rate ◽  
Ventricular Fibrillation ◽  
Exercise Training ◽  
Endurance Exercise ◽  
Submaximal Exercise ◽  
Treadmill Running ◽  
Vagal Activity ◽  
Endurance Exercise Training ◽  
Increased Risk ◽  
Exercise Onset

Both a large heart rate (HR) increase at exercise onset and a slow heart rate (HR) recovery following the termination of exercise have been linked to an increased risk for ventricular fibrillation (VF) in patients with coronary artery disease. Endurance exercise training can alter cardiac autonomic regulation. Therefore, it is possible that this intervention could restore a more normal HR regulation in high-risk individuals. To test this hypothesis, HR and HR variability (HRV, 0.24- to 1.04-Hz frequency component; an index of cardiac vagal activity) responses to submaximal exercise were measured 30, 60, and 120 s after exercise onset and 30, 60, and 120 s following the termination of exercise in dogs with healed myocardial infarctions known to be susceptible ( n = 19) to VF (induced by a 2-min coronary occlusion during the last minute of a submaximal exercise test). These studies were then repeated after either a 10-wk exercise program (treadmill running, n = 10) or an equivalent sedentary period ( n = 9). After 10 wk, the response to exercise was not altered in the sedentary animals. In contrast, endurance exercise increased indexes of cardiac vagal activity such that HR at exercise onset was reduced (30 s after exercise onset: HR pretraining 179 ± 8.4 vs. posttraining 151.4 ± 6.6 beats/min; HRV pretraining 4.0 ± 0.4 vs. posttraining 5.8 ± 0.4 ln ms2), whereas HR recovery 30 s after the termination of exercise increased (HR pretraining 186 ± 7.8 vs. posttraining 159.4 ± 7.7 beats/min; HRV pretraining 2.4 ± 0.3 vs. posttraining 4.0 ± 0.6 ln ms2). Thus endurance exercise training restored a more normal HR regulation in dogs susceptible to VF.

Endotoxin and myocardial failure: role of the myofibril and venous return

1978 ◽  
Vol 235 (2) ◽  
pp. H150-H156 ◽  
Author(s):  
F. D. Bruni ◽  
P. Komwatana ◽  
M. E. Soulsby ◽  
M. L. Hess
Keyword(s):  
Atpase Activity ◽  
Venous Return ◽  
Normal Activity ◽  
Left Ventricular ◽  
Myofibrillar Atpase ◽  
Myocardial Failure ◽  
Myofibrillar Atpase Activity ◽  
Myofibril Preparation

The effects of gramnegative endotoxin-induced myocardial failure in the pentobarbital-anesthetized dog were examined by monitoring its influence on cardiac myofibrillar ATPase activity. Myofibrils were isolated from endo- and epicardial portions of the left ventricular wall. ATPase activities were determined in animals treated with 4 mg/kg endotoxin and monitored 5 h, in animals monitored for 5 h without endotoxin (controls), and in animals implanted with a unilateral femoral shunt and given endotoxin. No differences were seen in the activities between the endo- and epicardial portions of any preparation. Activity was significantly depressed in endotoxemic animals. Increasing venous return by 313 +/- 71 ml/min significantly increased coronary flow by reducing coronary vascular resistance and prevented any observed depression of myofibrillar ATPase activity. In in vitro studies, adding endotoxin directly to a myofibril preparation did not modify normal activity. It appears that the mechanical and myofibrillar dysfunctions are due to the action of endotoxin at sites not associated with the actomyosin ATPase, but may be due to the production of an intermediary agent in concert with a decreased venous return.

Dissociation of myofibrillar atpase activity and contractile function in hypertrophied guinea pig hearts

1985 ◽  
Vol 17 ◽  
pp. 47-47 ◽  
Author(s):  
A WALDENSTROM ◽  
Y LECARPENTIER ◽  
M CLERGUE ◽  
P OLIVIERO ◽  
K SCHWARTZ ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Atpase Activity ◽  
Contractile Function ◽  
Myofibrillar Atpase ◽  
Myofibrillar Atpase Activity

Cardiac function and exercise training in conscious dogs

1977 ◽  
Vol 42 (6) ◽  
pp. 824-832 ◽  
Author(s):  
H. L. Stone
Keyword(s):  
Heart Rate ◽  
Exercise Training ◽  
Cardiac Function ◽  
Heart Rate Response ◽  
Exercise Program ◽  
Left Ventricular Pressure ◽  
Left Ventricular ◽  
Ventricular Pressure ◽  
Time Intervals ◽  
Similar Time

Exercise training (T) was accomplished in 21 mongrel dogs. The animals were instrumented to measure ascending aortic flow, left ventricular pressure, and left atrial pressure. They were allowed to recover for 4 wk following surgery before accomplishing a standardized submaximal test (SMT). The exercise program alternated daily between sprint and endurance training. During T, the animals were tested while lying quietly on a laboratory table as well as during the SMT. In six animals, ventricular function curves (VFC) were obtained by rapid volume loading at similar time intervals as the SMT. Heart rate increased during the SMT but was found to be reduced in the T animals by an average of 20 beats/min. The maximum derivative of left ventricular pressure (P) increased during the SMT in T animals by an average of 2,200 Torr/s above the untrained animals. The VFC was lower in T animals than untrained animals because of a reduction in heart rate response. Results indicate a reflex adaptation of the nervous system with training to improve cardiac function.

Thermal sensitivity of contractile function in chain pickerel, Esox niger

1985 ◽  
Vol 63 (4) ◽  
pp. 811-816 ◽  
Author(s):  
Bruce D. Sidell ◽  
Ian A. Johnston
Keyword(s):  
Atpase Activity ◽  
White Muscle ◽  
Contractile Function ◽  
Thermal Sensitivity ◽  
Muscle Fibers ◽  
Temperature Sensitive ◽  
Myofibrillar Atpase ◽  
Thermal Dependence ◽  
Tension Development ◽  
Myofibrillar Atpase Activity

Maximum catalytic activity and thermal sensitivity of Mg2+–Ca2+ activated myofibrillar ATPase from either red or white muscle tissue of chain pickerel is unaffected by 4–6 weeks acclimation to temperatures of 5 or 25 °C. Arrhenius plots of myofibrillar ATPase activity from red muscle are linear over the entire range of assay temperatures (2–32 °C; Q10 = 3.3). Similar plots of white muscle ATPase activity show a pronounced discontinuity at approximately 10 °C and a much greater thermal sensitivity below this temperature (Q10 = 11.2) than above it (Q10 = 2.2). Thermal dependence of myofibrillar ATPase activity from white muscle does not accurately predict the effect of temperature upon contraction velocities of isolated white muscle fibers. Contraction velocity of single chemically skinned white muscle fibers was sevenfold less temperature sensitive than ATPase activity below the 10 °C transition and 1.6-fold less temperature sensitive above this temperature (Q10 (0–27 °C) = 1.6). Maximum Ca2+-activated tension development was particularly temperature independent (Q10 = 1.2), ranging from 14 ± 1.6 N/cm2 at 5 °C to 20.9 ± 2.1 N/cm2 at 25 °C. Power output chain pickerel muscle, a product of these two parameters (force × velocity), should therefore show a relatively low thermal dependence (Q10 < 2) over the normal range of habitat temperatures.

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