Regeneration of the inferior vena cava with a bioabsorbable polymer implant: a histological study.
BACKGROUND
Cell implantation into ischemic regions has recently been introduced as a novel strategy for therapeutic angiogenesis. Little is known, however, about the process of blood vessel regeneration, particularly that of the inferior vena cava (IVC). The indicators of normal angiogenesis are also unestablished.


OBJECTIVE
To investigate the process of regeneration of the IVC from a histological viewpoint and to speculate on how the new formation and regeneration of the blood vessels proceed.


METHODS
Our previous studies showed that a bioabsorbable polymer patch implanted into the IVC formed vessels resembling the native IVC (J Gastrointest Surg 2005;9:789). Using this model system, we investigated the histology and time course of IVC regeneration in the graft site. A 3 x 2 portion of infrahepatic IVC was substituted by a bioabsorbable polymer patch of the same size in hybrid pigs. The patched area was excised for histology at 2 weeks and 3, 6, and 12 months after implantation (n = 3, each).


RESULTS
By 2 weeks, the patched area had developed vascular endothelial cells of the same type seen in native veins. The polymer implant was still detectable at 2 weeks but histologically absorbed at 3 months. Smooth muscle was barely formed at 2 weeks, but the ratio of smooth muscle to subendothelial connective tissue gradually increased as time advanced to 3, 6, and 12 months. Even at the last observation at 12 months, however, the amount of smooth muscle formed made up no more than one-half of the native IVC. The case with the elastic fibers accounted for about 90% of the total number of native fibers at 12 months. On gross examination, the patched area resembled the native IVC at 3 months after implantation.


CONCLUSIONS
These results demonstrated that the subendothelial tissue regenerated gradually, requiring more than 1 year to resemble native tissue, whereas the vascular endothelium regenerated in the early phase after injury. Our findings make it possible to establish criteria by which to evaluate venous regeneration.
Akimoto
Naoe
N
Department of Surgery, Saitama Medical University, Saitama, Japan.
Miyazawa
Mitsuo
M
Torii
Takahiro
T
Toshimitsu
Yasuko
Y
Aikawa
Masayasu
M
Okada
Katsuya
K
Otani
Yoshihide
Y
Koyama
Isamu
I
Ikada
Yoshito
Y
D020341:Absorbable Implants; D000818:Animals; D001807:Blood Vessel Prosthesis; D003094:Collagen / Q000378:metabolism; D004396:Coloring Agents; D004548:Elasticity; D004730:Endothelium, Vascular / Q000166:cytology / Q000502:physiology / Q000601:surgery; D004801:Eosine Yellowish-(YS); D006416:Hematoxylin; D023421:Models, Animal; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology / Q000601:surgery; D018919:Neovascularization, Physiologic; D011108:Polymers; D012038:Regeneration; D013194:Staining and Labeling; D013552:Swine; D014682:Vena Cava, Inferior / Q000166:cytology / Q000502:physiology* / Q000601:surgery*; D014945:Wound Healing; D014841:von Willebrand Factor / Q000378:metabolism
D004396:Coloring Agents; D011108:Polymers; D014841:von Willebrand Factor; D003094:Collagen; D004801:Eosine Yellowish-(YS); D006416:Hematoxylin