Cardiac ventricular muscle mechanical properties through the first year of life in Sprague-Dawley rats.

Advanced age has been shown to result in decreased compliance, shortening velocity, and calcium sensitivity of the heart muscle. Even though cardiac health has been studied extensively in elderly populations, relatively little is known about cardiac health and age for the first part of adulthood. The purpose of this study was to compare cardiac contractile properties across the first year of life in rats (between 17-53 weeks), corresponding to early to mid-adulthood. Hearts were harvested from rats aged 17-, 24-, 36-, and 53-weeks. Skinned cardiac trabecular fibre bundle testing was used to evaluate active and passive force properties, maximum shortening velocity, calcium sensitivity, and myosin heavy chain isoforms. Maximum active stress production was not different between age groups. Calcium sensitivity increased progressively, while shortening velocity remained unchanged after an increase from 17-and 24-weeks. Passive stiffness decreased between 17- and 24-weeks, but then increased progressively through to 53-weeks. Thus, many of the observed detrimental changes in systolic function (reduced shortening velocity and calcium sensitivity) associated with aging, do not seem to occur in early to mid-adulthood, while early signs of increased diastolic stiffness manifest within 53 weeks of age and may represent a first sign of decreasing heart function and health.