Altered energy supply to the pump function of the isolated heart of spontaneously hypertensive rats.

ABSTRACT

OBJECTIVE: The reasons for the development of cardiac insufficiency after a prolonged period of compensation accompanying myocardial hypertrophy are still uncertain and a disturbance in the energy metabolism of cardiomyocytes may serve as an underlying cause. The goal of the present work was to study functional and energetic correlates of the isolated heart of spontaneously hypertensive rats (SHR) at the stage of compensation. METHODS: Isolated hearts of SHR and normotensive age-matched Wistar-Kyoto (WKY) rats were subjected to volume and resistance loads. The myocardial content of high-energy phosphates and creatine was determined both before and after the functional loads. RESULTS: The contractile performances of the SHR hearts was significantly higher than those of the WKY hearts, the maximal cardiac output during volume load was higher by 36% and the maximal cardiac work index at complete aortic clamping was 68% higher. However, because the dry weight of SHR hearts was 48% higher, the normalized functional indices did not differ significantly between the groups. The ATP-to-ADP ratio and the total creatine level were significantly lower by 10% to 13% in the SHR group before and after the functional loads. In addition, the total adenine nucleotide pool and ATP content were 17% to 20% lower in SHR hearts after the functional loads. The content of high-energy phosphates correlated with contractile indices in the WKY group but not in the SHR group. CONCLUSIONS: The results showed that the SHR hearts were better adapted to increased loads than the WKY hearts; however, this advantage combines with an altered interrelation between myocardial energy state and its function.