Changes in Rat Aortic Actomyosin Content with Maturation

It has been reported by several investigators that the maximum active force generating ability (i.e., force/tissue cross-sectional area) of the aorta increases as the animal matures and then declines later in life. The purpose of this work was to determine if changes in the actomyosin content of the aorta occur during maturation which could contribute to the observed changes in force generating ability. The actin and myosin contents of rat thoracic aorta obtained from animals 3, 5, 7, 16 and 43 weeks of age were determined by quantitative gel electrophoresis, and were normalized with respect to tissue mass and protein and DNA contents. The results indicate that the amount of actomyosin (i.e., actin + myosin heavy chains) per tissue mass, protein and DNA increases rapidly during the first 5 weeks after birth and then remains constant. These observations suggest that the increasing actin and myosin heavy chain content of aorta observed early in life could explain in part the increasing force generating ability reported during this period, but that a loss of contractile material is not responsible for the reduction in force generating ability seen later in life.