Showing papers by "Edward G. Lakatta published in 1975"
TL;DR: It is concluded that the intrinsic inotropic response to catecholamines is diminished in the aged myocardium and this finding does not appear to result from differences in tachyphylaxis, tissue uptake of catechlamines, or the ability of the contractile proteins to respond to increasing concentrations of calcium but instead may result from a decreased ability of ctcholamines to increase the intracellular calcium available for contraction.
Abstract: The effect of advanced age on the response of active tension, maximal rate of tension development (dT/dt), and contraction duration to catecholamines and to calcium was evaluated in isometric trabeculae carneae from young adult (6-month-old), middle-aged (12-month-old), and aged (25-month-old) rats. Control values were not age dependent except for that for contraction duration which was prolonged in the aged group. At a norepinephrine concentration of 8 times 10-5M, dT/dt increased to 163.8 plus or minus 5.3% of control in the young adult group and to 125.9 plus or minus 6.3% of control in the aged group (P smaller than 0.001). Active tension increased to 121.3 plus or minus 4.0% of control in the young adult muscles but did not increase in the aged muscles (P smaller than 0.01). Contraction duration shortened proportionately in both age groups. Similar results were obtained with isoproterenol. In contrast to the response to catecholamines, there was no age difference in the response of active tension and dT/dt to increasing concentrations of calcium. It is concluded that the intrinsic inotropic response to catecholamines is diminished in the aged myocardium. This finding does not appear to result from differences in tachyphylaxis, tissue uptake of catecholamines, or the ability of the contractile proteins to respond to increasing concentrations of calcium but instead may result from a decreased ability of catecholamines to increase the intracellular calcium available for contraction.
329 citations
TL;DR: The greater electromechanical dissociation and greater overshoot in contraction duration following hypoxia in aged myocardium suggests that prolonged contraction duration in agedMyocardium results from a prolonged active state rather than changes in passive properties or myocardial catecholamine content.
Abstract: Isometric performance at 29degreesC was measured in left ventricular trabeculae carneae from young adult (6-mo) and aged (25-mo) rats (n equals 18 in each group). Active tension and maximal rate of tension development did not differ with age, but contraction duration was 255plus or minus6 ms in the young adult and 283plus or minus6 ms in the aged group (P less than0.001). Although catecholamine content per gram heart weight was less in the aged myocardium, additional experiments showed that neither 1 times 10-6 M propranolol nor pretreatment with 6-hydroxydopamine eliminated the age difference in contraction duration. To determine if this age difference resulted from a prolonged active state, electromechanical dissociation and the overshoot of contraction duration during recovery from hypoxia were measured. During paired stimulation greater mechanical refractoriness was found in aged muscles (P less than0.01), but intracellular action potential recordings showed no age difference in the electrical refractory period. On recovery from hypoxia, contraction duration overshoot was 117plus or minus 4percent of control in the young and 138plus or minus 4percent of control in the aged muscles (P less than0.01). The greater electromechanical dissociation and greater overshoot in contraction duration following hypoxia in aged myocardium suggests that prolonged contraction duration in aged myocardium results from a prolonged active state rather than changes in passive properties or myocardial catecholamine content.
191 citations
TL;DR: The relationship between the magnitude of epicardial ST-segment elevation and intramyocardial oxygen tension after coronary artery ligation was examined in 11 dogs at various coronary perfusion pressures.
Abstract: The relationship between the magnitude of epicardial ST-segment elevation and intramyocardial oxygen tension after coronary artery ligation was examined in 11 dogs at various coronary perfusion pressures. The ST map significantly reflected local intramyocardial oxygen tension, and the level of coronary perfusion pressure proved to be an important determinant of both local myocardial oxygen balance and the magnitude of ischaemic injury.
43 citations
01 Jan 1975
4 citations
01 Jan 1975
TL;DR: The direct inotropic response to left ventricular traveculae carneae from young adult and aged rats was examined during exposure to catecholamines to define the role of the myocardium in these age associated changes.
Abstract: It is known that the cardiovascular response to stress in both intact animals and in man diminishes with advancing age. In order to define the role of the myocardium in these age associated changes, the direct inotropic response to left ventricular traveculae carneae from young adult (6 mo) and aged (24 mo) rats was examined during exposure to catecholamines. The muscles were stimulated to contract isometrically at 24 beats per min at 29°C Krebs-Ringer bicarbonate solution, modified by lowering the Ca++ to 1 . 0mM, the Mg++ to 0 . 6mM, and by adding glucose to a concentration of 16mM. At control, active tension (AT) , maximum rate of tension development (dT/dt) and contraction duration (CD) , measured as the interval from the onset of tension development to the time tension fell to one-half of its maximum value were:
2 citations