[Intravital and electron microscopic observations on increased vascular permeability to light mechanical stimulation]

The purpose of the study was to investigate the early response of microvasculature, especially increased vascular permeability (IVP) to the light-continuous mechanical pressure stimulation. The hamster cheek pouch was used as an in vivo model of periodontal vasculature. FITC-dextran (molecular weight 150,000) was injected intravenously as a tracer and then intravital and electron microscopic observations were made and also the role of histamine in IVP to the mechanical stimulation was studied. The results were as follows: 1. Blood flow in postcapillary venules (PCV) (about 50 microns in diameter) was not interrupted under the stimulation of 0.1g. IVP at PCV was observed at 5 minutes after the beginning of this stimulation by fluorescein intravital microscopy. 2. Electron microscopic observations revealed that this IVP was attributed to the formation of gaps (0.1 approximately 0.5 microns) between endothelial cells of PCV without stasis and degranulation of mast cells and that monocytes and platelets were attached to the endothelial cells in the lumen. These gaps were seen until 30 minutes after the beginning of the stimulation. 3. Pretreatment with pyrilamine, a histamine H1-receptor antagonist, inhibited the appearance of IVP at 5 minutes after the beginning of the stimulation, but it didn't completely reduce IVP appearing after 10 minutes of stimulation. It was suggested that histamine played some roles in IVP which appeared at 5 minutes after the beginning of the stimulation, but was not essential after 10 minutes.