Structural and biochemical properties of the rat myocardium after 21 days of head-down suspension.

The effects of 21 d of head-down suspension on the biochemical and structural properties of the myocardium were determined in male rats (HDS, n = 10), and compared with control non-suspended animals (C, n = 10). HDS rats were prepared using Morey's tail-suspension model, and maintained at 45 degrees tilt. At the end of the conditioning period, hearts were excised and dissected into right (RV) and left plus intraventricular septum (LV). We observed that HDS rats had lower LV- and RV-absolute weights than C animals (-8.5%, p < 0.05, and -12%, p < 0.05, respectively). The relative ventricle weights (ventricle weight/body weight, mg.g-1) were unaffected by HDS. Native myosin isoform analysis revealed that HDS did not alter myosin expression in both LV and RV. The capillary bed, examined using histochemical methods, was found to be unaffected by HDS. A significant decrease in the lactate dehydrogenase activity was detected in LV after 21 d of HDS (-16%, p < 0.05). Collectively, these results suggest that the early neurohumoral changes occurring in response to HDS-induced hemodynamic overload are sufficient to prevent any alteration in the biochemical and structural properties of the myocardial tissue.