[Aging of heart function in animals].
Most of the laboratory animals studied for cardiovascular ageing are rodents. Anatomical studies have demonstrated an increase in heart weight and volume, hypovascularization of the myocardium and, more recently, hypertrophy of myocytes. Studies on the mechanical properties of rat papillary muscle have shown that ageing is associated with reduction of myocardial distensibility, whereas the habitual parameters of contractility (Tmax and Vmax) are unchanged in terms of baseline values. On the other hand, mechanical responses to stimulation of beta-adrenoceptors are reduced. The essential change in myocardial contraction in ageing rats is its chronology: ageing is attended by a longer duration of both contraction and relaxation. Biochemical studies of old rats' myocardium have yielded a fundamental information: in this species ageing is accompanied by a change in synthesized myosin subtype. This change is identical to that observed in experimental systolic overload; it is also adaptative, as it enables oxygen consumption to be reduced during a constant work, and it explains the modifications observed in the chronology of a contraction. Studies on the "pump" function of old rats' myocardium have confirmed the appearance with age of another adaptative change: isolated hearts of old animals have a greater output in a rigid circuit while the hearts of adult rats have their output in a more compliant circuit. Altogether, experimental studies on cardiac ageing lead to the conclusion that the changes observed are similar to those due to systolic overload, the origin of which is a loss of arterial compliance. These changes are adaptative in that they reduce oxygen consumption by a myocardium with systolic overload, but the resulting changes in contraction chronology are such that the aged heart cannot deviate from a mean rate without notably widening the differential blood pressure. Thus, experimental studies of myocardial ageing have presented ageing as a contradiction between ideal adaptation to a chronic stress and reduced possibilities of adaptation to acute aggressions.
Sebban
C
C
Laboratoire de Biologie du Vieillissement, Hôpital Charles-Foix, Ivry-sur-Seine.
Yazdani
B
B
D000375:Aging / Q000473:pathology / Q000502:physiology*; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D003187:Compliance; D009200:Myocardial Contraction / Q000502:physiology; D009206:Myocardium / Q000378:metabolism / Q000473:pathology*; D009218:Myosins / Q000378:metabolism; D051381:Rats; D013318:Stroke Volume / Q000502:physiology
D009218:Myosins
Vieillissement de la fonction cardiaque chez l'animal.