| Fracture healing is a complex process in which wound tissue repair, fibrous tissue develop osseous tissue and a lot of molecular factors make their regulative effect. Nervous system play an important role in the process of fracture healing, Neuropeptides been released by sensory system when fracture happened and take active part in cell preferation and differentiation[1]. Vasoactive intestinal peptide be made of 28 amino acid, it is an important neuroendocrine molecular and distribute at central nervous system and peripheral nervous system[2].As an important neuropeptide,VIP take part in the process of soft tissu repairing and fracture healing. But it's mechanism act at the fracture healing and act with other growth factores is still unclear.It has been verification through many experiments that vascular endothelial growth factor(VEGF) is an important growth factor to promote differentiation and immigration of endothelial cells and increase the permeability of endothelial cells and promote neovascularization[3].According to some relative documents,VIP can promote some endothelial cells synthesis VEGF,such as lung cancer cells and prostatic carcinoma cells.then VEGF combinate with the receptor on the membrane of vascular endothelial cells and booste the proliferation of vascular endothelial cells and the formation of the blood vessels[4-5]. The main goal in the study is to understand the rule of the expression of VIP and the change of microvessel density(MVD) in the new callus by using the model of the fracture of mandible with the loss of the inferior alveolar nerve(IAN),to investigate the relationship between the quality,speed and the ways of the healing of callus during fracture healing,and through the culture of human umbilical vein vessel endothelial cells(HUVECs),to observe the effect of the proliferation of HUVECs and the synthesis of VEGF when VIP stimulate HUVECs,and to investigate the effect and the possible mechanisms of VIP having during the fracture healing process.Methods:1. Animal experiments: In the experiment, we improved the model of the mandible fracture with the loss of IAN which had been used in the past experiments, Every experimental rabbit was made fracture on both sides of mandible: right sides have been made simple mandible fracture (n=35), left sides have been made the mandible fracture with transaction of inferior alveolar nerve + simple mandible fracture (n=35). The fractured bone tissue were obtained and paraffin slices were made after the death of seven experimental ribbits at the 7,14,21,28,35th day after the surgery respectively.The quality of the fresh Callus,the speed and the ways of the fracture healing were detected by these methods which are histochemistry(HE) and immunohistochemical staining, The relationship between the expression of VIP and MVD in callus tissue among the denervation mandibular fracture sides and simple mandibular fracture sides were analyzed using the image analyzed software in computer.2. Cell culture:In order to understand if VIP has the effect to improve the proliferation of vascular endothelial cells and it's mechanism, HUVECs were cultured in vitro, and VIP were added in the culture medium, The proliferation of HUVECs and the synthesis of VEGF have been detected apply the method of Mono-nuclear cell direc cytotoxicity assay (MTT) and the method of enzyme-linked immunosorbentassay (ELISA) respectively.Results:1. Animal experiment results: (1) Compare with the simple mandible fracture sides, there have some irregular bone trabecula and more osteoid in the fresh callus in the denervation mandible fracture sides. (2)Results show that there are few VIP immunoreactive nerve fibers in callus at 7th day after IAN transaction mandible fracture, while a lot of VIP immunoreactive nerve fibers in callus throughout the repair process in control sides which have shown that experimental model of both sides are successful. (3)In the simple mandible fracture sides, there are few vascular endothelial cells at the 7th day, more at the 14,21,28th day, and few at the 35th day after the fracture. Compare with the simple mandible fracture sides, there are less vascular endothelial cells at the five stages in the denervation mandible fracture sides.2. Cell culture results: (1)VIP can promote the proliferation of HUVECs significantly. (2)VIP can improve the synthesis of VEGF in HUVECs. Conclusions:(1) IAN can affect the mandible fracture healing,VIP is one of the important neuropeptides that take part in the fracture healing.(2)The concentration of VIP in the location of the fracture can affect the quality of the callus, and can be decreased result in the loss of IAN, and make the biomechanical intensity of the callus to lower and cut down the speed of the fracture healing simultaneous.(3)It has impotant effect to regulate the fracture healing,because of the distinct of the expression of VIP during the different fracture healing stages. There have a positive correlated relationship between the expression of VIP and the chang of microvessel density(MVD). These results show that VIP could improve the formation of the new vessels in the location of the fracture. (4)VIP have the function to promote the proliferation of HUVECs which have been activated possibly by VEGF up-regulated in the HUVECs by VIP. (5)It is one of the important mechanisms of regulation the fracture healing for VIP to improve the formation of the fresh blood vessels in the location of the fracture.
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