Effect of a 14-day hindlimb suspension on beta-adrenoreceptors in rats

Exposure to long-term simulated microgravity exhibits reduced sympathetic n ervous system activity. This study tested the hypothesis that the hypersens itivity of adrenoreceptors would explain partly many other features of the hemodynamic consequences of return from space. The biochemical properties o f the beta adrenoreceptors (beta AR) were determined using I-125-cyanopindo lol (I-125-CYP) binding in three rat groups: (I) The first experimental gro up consisted of 24 h-restrained orthostatic rats in the horizontal position , to test the early effect of the attachment to the suspension device; (2) the second experimental group consisted of 24 h-restrained antiorthostatic rats, to test the early effect of the suspension; (3) the third experimenta l group consisted of 14 day-restrained antiorthostatic rats, to test the lo ng term effect of the suspension. The study was performed in two organs inv olved in blood pressure regulation, i.e, the heart (atria and ventricles we re separated) and kidneys. The Scatchard analysis of I-125-cyanopindolol bi nding in both organs indicated no significant alterations in the dissociati on constant (K-d) and the maximum binding capacity (B-max) in the three exp erimental groups. These results do not allow the conclusion about the SNS a daptation pattern to simulated microgravity. Thus, the hypothesis that PAR are involved in the cardiovascular adaptation to simulated microgravity is not verified in this model where, as a matter of fact, cardiovascular decon ditioning is not verified even if this model is widely used. (C) 1999 Elsev ier Science Inc. All rights reserved.