The effect of long-term tilting on capillary supply in rat hindlimb muscles

Rats were kept for three weeks tilted head-up at 45 degrees and their capillary supply (capillary density CD, number of capillaries/mm2, and capillary/fibre ratio C/F), fibre density FD, and muscle weights were compared with a group of animals with similarly restricted movement but at horizontal position, and with control freely moving animals. Movement restriction caused loss of muscle (but not body) weight in fast muscles in all rats, and gain of weight in slow postural soleus in the tilted group. Neither of these changes were due to changes in the content of water. Loss of weight was accompanied by increased fibre density indicative of muscle atrophy due to movement restriction. Capillary supply was not affected by movement restriction, but was significantly decreased, particularly in the oxidative part of tibialis anterior and in the soleus of tilted animals (C/F: 1.78 +/- 0.11 vs 2.11 +/- 0.05 and 2.06 +/- 0.08 vs 2.29 +/- 0.10). It is assumed that this reduction might be explained by changes in hemodynamic characteristics of the venous vascular bed due to a chronic increase in hydrostatic pressure load.