Aims: 

Alteration of hemodynamic parameters induce network and segmental remodelling in arterial networks. These processes are less known at the venous side of the circulation. The effects of elevated venous pressure with reduced flow, induced by chronic partial venous occlusion were studied in rats on the development of the collateral venous network as well as on the biomechanical and histological properties of the affected main branch.

Methods: 

The main branch of the saphenous vein of the rat was partially clipped reducing its diameter to ~500 mm. Four, eight and twelve weeks later a cylindrical segment of it was subjected to an in vitro videomicroscopic biomechanical test. The developing collateral network was studied using plastic casts and with intravital video-microscopy. The surrounding tissue was investigated by immuno-histochemistry.

Results: 

Involution of the lumen and of the wall of the affected main branch was observed. Its relaxed inner diameter measured at 10 mmHg pressure decreased from 613±17 to 455±29 mm in four weeks, while the thickness of the wall was reduced from 129±20 to 92±8 mm in eight weeks (compared to the unaffected control side, p<0.05). A rich collateral network, emerged from the tiny vasa vasorum branches has been built, and in these branches retrograde flow was detected. The plastic casts showed the development of the collateral network in space and time. From the original network, some branches with typical corrugated courses obtained larger diameter, visibly the effect of larger flow in them. Angiogenesis in the surrounding tissue was shown also by immuno-histochemistry (Ki67 cellular division activity and smooth muscle actin).

Conclusion: 

Transmural pressure has been thought to be the leading cause for venous network and wall remodelling. We found that in addition to altered pressure, chronic flow changes have a more decisive role than thought earlier.