Fetal hepatic artery ligation suppresses liver hematopoiesis in utero

Introduction: Fetal hematopoiesis involves a successive interchange of progenitor cell activity among different anatomical sites, with the liver playing a pivotal role in the sequence. The mechanisms that regulate this unique process may hold the clues to the treatment and possibly cure of numerous hematological and non-hematological diseases, both before and after birth. We hypothesized that fetal hepatic hematopoiesis is controlled by arterial blood flow to the liver. This study was aimed at determining the effects of changes in hepatic artery flow upon liver hematopoiesis in utero. Methods: The experimental design was validated by previous data demonstrating (1) the negligible role of arterial blood flow on fetal hepatic oxygenation and (2) an increase in hepatic arterial flow as a consequence of biliary obstruction. Fetal lambs (n=15) were divided into 3 groups at 106-113 days gestation (term=145 days). Group I (n=5) underwent ligation and division of the right and left hepatic arteries; group II (n=4) underwent ligation and division of the common bile duct; and group III (n=6) were sham-operated controls. Euthanasia was performed at comparable gestational ages near term, 23.7+/-6.4 days postoperatively. Animals were blindly assessed for hepatic hematopoietic cell/island density by both standard histology and transferrin receptor (CD71) immunohistochemistry. Additional analyses included hepatic angiography, peripheral blood hemoglobin (Hb) content, and colony-forming unit (CFU) assays of hematopoietic progenitors. Statistical comparisons were by non-parametric and mixed model regression analyses, as appropriate (P<0.05). Results: Overall fetal survival was 93%. In group I, post-mortem arteriograms confirmed complete occlusion of the hepatic arteries, albeit with variable local collateralization. There was a significant reduction in the density of hematopoietic progenitors in group I, when compared to groups II and III (Figure). This was further confirmed by a significant reduction of CFU in group I. Group II had a significantly higher density of hematopoietic progenitors than the other two groups. Fetal Hb levels were lower in group I when compared to groups II and III, but this did not reach statistical significance in this series. Conclusions: Fetal hepatic hematopoeisis is dependent on arterial blood flow to the liver. These data demonstrate a unique and previously unrecognized role of the hepatic artery in fetal development. Fetal hepatic artery ligation is a novel surgical model for the study of fetal hematopoiesis.