Endothelin-1 expression in the microvasculature of normal and 3-hour continuously loaded rat molar periodontal ligament.

Endothelin-1 (ET-1) distribution is described in the microvascular bed (MVB) of normal rat molar periodontal ligament (PDL). Five male Sprague-Dawley rats, aged 90 days, were anaesthetized and an external pressure of 100 +/- 20 g, maintained for 3 hours, was transmitted occlusally to randomly allocated left or right molars. The controls were the contralateral molars. Rats were perfused for 5 minutes with 5 per cent paraformaldehyde, and the mandibles post-fixed and stored in 30 per cent sucrose. Sagittal, undemineralized, mandibular jaw sections, approximately 150 microns thick, were immunolabelled with ET-1 and alpha-smooth muscle actin (alpha-SMA) primary antibodies, and IgG/CY5 and IgG/CY3 secondary antibodies, respectively. Serial images were captured with a Bio-Rad MRC-1000 UV confocal laser scanning microscope (CLSM). In the control PDL, the ET-1 immunolabelling occurred sporadically in all categories of PDL blood vessels. ET-1 showed a punctate distribution within endothelial cells, producing longitudinal and circumferential pan-endothelial labelling. Immunoreactivity to the ET-1 antibody occurred at or adjacent to vessel branching sites, and affected blood vessels with and lacking alpha-SMA immunolabelling. Treatment effects on ET-1 immunofluorescence were analysed for vascular endothelium, socket bone surface cells, cementum surface cells and PDL background in the cervical, inter-radicular and apical regions. Significant (P < 0.05) region by treatment interactions occurred for the endothelium and bone. Cementum showed a significant (P < 0.05) region effect and a significant (P < 0.05) treatment effect. However, the region by treatment interaction was not significant. Background immunofluorescence showed significant (P < 0.05) region by treatment effects for the endothelium and bone. ET-1 activity is the default state for normal PDL vascular endothelium.