Prolonged contraction duration in aged myocardium.

Abstract

A B S T R A C T Isometric performance at 29'C was measured in left ventricular trabeculae carneae from young adult (6-mo) and aged (25-mo) rats (n = 18 in each group). Active tension and maximal rate of tension development did not differ with age, but contraction duration was 255±6 ms in the young adult and 283±6 ms in the aged group (P < 0.001). Although catecholamine content per gram heart weight was less in the aged myocardium, additional experiments showed that neither 1 X 10' 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 < 0.01), but intracellular action potential recordings showed no age difference in the electrical refractory period. On recovery from hypoxia, contraction duration overshoot was 117±4% of control in the young and 138±4% of control in the aged muscles (P < 0.01). 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.

Hormone-sensitive fat cell adenylate cyclase in the rat. Influences of growth, cell size, and aging.

“…By 24 mo the colony exhibits a 50%o mortality, and animals at this age are considered to be senescent. Other characteristics of this rat colony have recently been described (5). All animals were maintained on a standard ad lib.…”

Fatiguing exercise initiated later in life reduces incidence of fibrillation and improves sleep quality in Drosophila

“…These changing profiles of cardiac function during aging have been exhibited in older humans. For example, the aged exhibit an increase in diastolic end-filling, resulting in an increase of contraction duration (Lakatta et al 1975;Rodeheffer et al 1984). This increased contraction duration, in turn, leads to a reduction in resting heart rate and an even more pronounced reduction in maximal heart rate during exercise.…”

Effet de l'âge et de la compliance du circuit d'éjection sur les courbes de fonction cardiaque et les pressions systoliques du coeur isolé de rat

“…Il a été observé chez l'homme âgé que la durée de la diastole augmentait significativement quand la compliance ventriculaire diastolique diminuait [20]. Ces deux faits sont peut-être à rapprocher d'autant qu'une diminution avec l'âge de la distensibilité du muscle papillaire de rat a été plusieurs fois rapportée [6,10,22].…”

“…Le vieillissement du système cardiovasculaire est caractérisé par deux modifications essentielles: -une prolongation de la durée d'une contraction concernant la phase de mise en tension et la phase de relaxation [10], -une altération du tissu conjonctif cardiaque et artériel [11,17,24] modifiant les propriétés mécaniques de ces organes dans le sens d'une rigidité accrue [8,12,15,16]. Les conséquences de ces phénomènes, mis en évi-dence sur des fragments de muscle ou d'artère, sur la fonction pompe du coeur sont encore très mal appré-ciées.…”