[Ultrastructural changes of arterial wall from different body parts of rats during simulated weightlessness]

To test the nature of remodeling of arteries in different body parts in adapting to local hemodynamic changes induced by tail-suspension.

Ultrastructural changes of hindlimb and cerebral arteries from 4-wk tail-suspended (SUS-4), 1-wk recovered (REC-1), and control (CON) rats were studied by transmission electron microscopy.

For the hindquarter arteries, like the femoral artery and anterior tibial artery, there were fewer smooth muscle layers, less myofilaments in the smooth muscle cell (SMC), and more intercellular substance in SUS-4 group than in CON group. After 1-wk recovery, the internal elastic lamina of the arteries thickened, the amount of myofilaments in SMC increased, the content of intercellular substance restored, and neoformative SMCs emerged under the endothelium. With respect to arteries in the neck region and the brain, like the common carotid artery and basilar artery, SMCs of contractile phenotype were converted to that of synthetic phenotype, and migration and hyperplasia of SMCs also happened. After 1-wk recovery all these alterations were somewhat restored.

It provided further evidence that peripheral effector mechanism might play an important role in the genesis of postflight orthostatic intolerance.