G-induced myocardium functional alterations are not related to structural changes in rat heart

Abstract

Background: Left ventricular myocardial hypertrophy with a redistribution of the isomyosins is classically observed under chronic pressure overload.

Hypothesis: Structural changes will also occur in myocardial cells after repeated exposures to high sustained +Gz acceleration.

Method: Rats were exposed to three plateaus of 30 s at 10 +Gz, 4 times a week, for 4 weeks. The myocardial mass was evaluated by measuring the ratio between left ventricular weight and body weight, and the myocardial fiber cross-sectional area. Changes in capillary density were evaluated using the myosin ATPase method. The distribution of myosin isoforms was determined by electrophoresis.

Results: Contrary to expectations, no myocardial hypertrophy developed, and no transition was observed in myosin isoforms of centrifuged rats.

Conclusion: The functional mechanical and energetic transformations observed in a previous investigation using an identical experimental protocol probably took place at an early stage of myocardial adaptation to +Gz acceleration. We conclude that our protocol of repeated +Gz exposures is a model of chronic overloading very different from classical models.