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

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.