Comprehensive analysis of the regenerating mouse liver:: An in vivo fluorescence microscopic and immunohistological study

Background. Regeneration of tissue is a fundamental parameter of the liver's response to injury and is essential for post-operative recovery from hepatic resection. An adequate microvascular supply of both remnant tissue and newly formed cell clusters is necessary for the accurate restoration of the organ. However, a comprehensive analysis of hepatic architecture and microcirculation during liver regeneration is missing. Methods. Using intravital high resolution multifluorescence microscopy and histological techniques we analyzed the regenerating liver of mice at days 3, 5, and 8 after 68% hepatectomy. Results. Within the 8-day course of regeneration, liver weight restored to similar to 90% of its original mass. During the 8-day period of observation density of hepatocytes and Ito cells was constantly found reduced from 4,200 and 800 cells/mm(2) in non-hepatectomized control livers to similar to 2,500 and similar to 500 cells/mm(2). A transient decline of sinusoidal density was partly compensated by recruiting all sinusoids for perfusion with a final perfusion index of 79, 89, and 98% at days 3, 5, and 8 after resection. Increase of sinusoidal diameters preserved functional vessel area after resection, guaranteeing an adequate tissue oxygenation, as verified by low parenchymal NADH autofluorescence. The number of PCNA expressing hepatocytes rose 11-, 4-, and 2-fold at days 3, 5, and 8 after resection, followed by a maximum proliferation of sinusoidal lining cells at day 5. Cell apoptosis slightly increased, most probably in response to the restoration and to eliminate redundant cells. Liver regeneration was not associated with enhanced leukocyte-endothelial cell interaction, disproving inflammation as a relevant trigger for the regeneration. Conclusion. The present data contribute to a better understanding of the complex vascular and cellular mechanisms during liver regeneration to develop strategies fighting against impeded liver growth. (c) 2006 Elsevier Inc. All rights reserved.