Angiogenic induction and cell migration in an orthopaedically expanded maxillary suture in the rat

The purpose was to examine the effect of an angiogenic factor on cell migration patterns and osteoblast histogenesis during the 96 h following orthopaedic expansion of the anterior maxillary suture. Fifty rats were divided into four groups: (1) a control group that received only angiogenic induction via injection of 5 ng/g body wt recombinant human endothelial-cell growth factor; (2) an experimental group that received orthopaedic expansion and angiogenic induction; (3) a sham group that received orthopaedic expansion and normal saline injection; and (4) a baseline group that received no expansion or injection. The experimental and sham groups were subdivided to conduct experiments over 1, 2, 3 or 4 days. The anterior portion of each maxilla was dissected free and demineralized. Sections (4 μm thick) were cut from every block and stained with Mayerʹs haematoxylin and eosin. Cell migration was analysed using a previously established cell-kinetics model. The osteoprogenitor cells were divided into four categories according to nuclear volume: A cells (40–79 μm3), B cells (80–119 μm3), C cells (120–169 μm3), and D cells (⩾ 169 μm3), A′ cells are the portion of the A cell population that responds to osteogenic stimulus. As previously defined in periodontal ligament, the reciprocal association of a decreasing number of less differentiated (A + A′) cells and an increasing number of C + D cells, as a function of distance from the nearest major blood vessel, was consistently found in all groups. This suggests a vascularly oriented gradient of progressively more differentiated osteoprogenitor cells. Also, A + A′ cells were predominately located within 20 um of the nearest major blood vessel whereas the C + D cells were found at a distance > 30 μm from the nearest major blood vessel. These results suggest that the A′ → C shift occurs 20–30 μm from the nearest major blood vessel. In the angiogenic induction groups, the numbers of committed osteoprogenitors (A + A′) were significantly higher than in the sham group at day 1. At day 3, the numbers of preosteoblasts (C + D) in angiogenic sutures were significantly higher than in the sham groups. This enhancement of preosteoblast population strongly suggests the possible role of activated pericytes in expanded sutures as a source of osteoprogenitor cells.