Reduced myocardial actomyosin adenosine triphosphatase activity in the ageing male Fischer rat.

Actomyosin was extracted from myocardial homogenates from male rats of different ages of a long-inbred Fischer rat colony maintained under controlled conditions of temperature, humidity, and light. ATPase specific activity rose to a maximum at 2 months of age; this was followed by a progressive decline by about 25% at 16 months of age. However, the extractable actomyosin remained constant during this period. This loss in actomyosin ATPase specific activity is in good agreement with previously reported decrements in both stroke index and myocardial calcium content and an increase in myocardial contraction duration in aged rats.