Cardiac energetics in short and long term hypertrophy induced by aortic coarctation.

Hypertrophy was induced in rats by constriction of the abdominal aorta proximal to the coeliac trunk. The effects of both short-term, STH. (2 to 4 days) and long term, LTH (40 to 55 days) hypertrophy were studied by mechanical and myothermic measurements on papillary muscles from the left ventricle. In agreement with other studies aortic coarctation increased the left ventricle to body weight ratio. In isometric experiments it was shown that peak stress development was enhanced in the STH group compared with the control and LTH groups. Active heat production was related to active stress development by linear regression in the control and pressure overload groups. There was no significant difference between the mean slopes of the groups but there was a significant increase in the intercept in the STH group and a decrease in the LTH group. This intercept corresponds to the tension-independent heat component. In isotonic experiments load enthalpy relationships were determined for the different groups and the data for each group were pooled. In the LTH group there was a 19% fall in work output per contraction and a 20% fall in total enthalpy. In the STH group there was a 31% increase in work output and a 39% rise in total enthalpy. Because of the parallel changes in work and enthalpy there was no significant change in the mechanical efficiency of the two groups as compared to the controls. The simplest interpretation of the results is that in STH the intracellular free calcium level is raised whereas in LTH it is lowered.