Cardiac adaptations to aortic constriction in adult and aged rats.

Myocardial function in vitro and myosin heavy chains (MHCs) were studied in control and hypertrophied hearts of adult (9-10 mo) and aged (25-28 mo) female Fischer 344 rats 7 days after aortic constriction. Aortic constriction increased left ventricular mass to 110 and 112% of the control values of 484 +/- 12 and 617 +/- 18 (SE) mg in adult and aged rats, respectively. After aortic constriction, there was a significant age-related difference in the adaptation of peak pressure development in vitro, as peak left ventricular systolic pressure increased and decreased in hearts of adult and aged rats. The maximum rate of pressure development in control hearts of aged rats was 79% of the adult value of 11,264 +/- 1,527 mmHg/s; hypertrophy did not alter values of either age group. alpha-MHC accounted for 82 +/- 1 and 48 +/- 3% of the total left ventricular MHC for the adult and aged control groups, respectively, and values were not altered by aortic constriction. With hypertrophy 7 days after aortic constriction, there is an impairment in the adaptation of left ventricular function in hearts of aged compared with adult rats. This impairment is not explained by alterations in MHC isoform.