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 followi ng 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 receiv ed orthopaedic expansion and angiogenic induction; (3) a sham group th at received orthopaedic expansion and normal saline injection; and (4) a baseline group that received no expansion or injection. The experim ental 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 mu m thick) were cut from every block and stained with Mayer's haematoxylin and eosin. Cell migration was an alysed using a previously established cell-kinetics moder. The osteopr ogenitor cells were divided into four categories according to nuclear volume: A cells (40-79 mu m(3)), B cells (80-119 mu m(3)), C cells (12 0-169 mu m(3)) and D cells (greater than or equal to 169 mu m(3) A' ce lls are the portion of the A cell population that responds to osteogen ic stimulus. As previously defined in periodontal ligament, the recipr ocal association of a decreasing number of less differentiated (A + A' ) cells and an increasing number of C + D cells, as a function of dist ance from the nearest major blood vessel, was consistently found in al l groups. This suggests a vascularly oriented gradient of progressivel y more differentiated osteoprogenitor cells. Also, A + A cells were pr edominately located within 20 mu m of the nearest major blood vessel w hereas the C + D cells were found at a distance > 30 mu m from the nea rest major brood vessel. These results suggest that the A' --> C shift occurs 20-30 mu m from the nearest major blood vessel. In the angioge nic 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 sig nificantly higher than in the sham groups. This enhancement of preoste oblast population strongly suggests the possible role of activated per icytes in expanded sutures as a source of osteoprogenitor cells. Copyr ight (C) 1997 Published by Elsevier Science Ltd.