Arterioles undergo major morphological changes during vasoconstriction. These changes consist of formation of an orderly pattern of periluminal ridges whose size and number vary systematically with the level of constriction. The cellular interactions which produce these changes have not been studied in detail, hence little is known about how the arteriolar wall coordinates rearrangement of its components as the vessel changes its diameter. The purpose of the present study is to explore the relationships between the degree of microvessel constriction, mural configuration, and the frequency and distribution of myoendothelial junctions (MEJ's). The working hypothesis is that points of attachment between the arteriolar endothelium and smooth muscle (i.e. MEJ's) provide focal areas of force transduction between these two cell types, and thereby determine deformations in the wall which occur by selectively exerting force along the luminal perimeter. The present study seeks to address this issue by undertaking an ultrastructural analysis of MEJ's in both dilated and constricted arterioles. Knowledge of the mechanical interactions between the cell of the arteriolar wall is important to our understanding of the pathology of hypertension and other cardiovascular lesions (e.g. cerebral vasospasm). To obtain arteriolar vessels for ultrastructural analysis, male golden hamsters are anesthetized with sodium pentobarbital (IP) and tracheostomized. Supplemental anesthetic is administered through a femoral vein cannula. The left cheek pouch is gently exposed, prepared for intravital observation as previously described (Duling, 1973) and suffused with a physiological salt solution at pH 7.4. Arterioles displaying appropriate responses to vasoactive substances are selected as experimental vessels. Vessels dilated with adenosine or constricted with norepinephrine are fixed for ultrastructural analysis in situ by immersing the entire pouch in fixative. Thin cross sections of arterioles are cut, stained and examined with a TEM. The frequency and distribution of MEJ's present in both dilated and constricted microvessels will be compared. Morphometric analysis of vessel cross sections will determine: 1) If MEJ's are labile entities, 2) any organized array of MEJ's associated with the periluminal ridges of constricted vessels, 3) the type of MEJ's extant between the endothelium and smooth muscle (e.g. tight junction, gap junction, etc.) and 4) the cellular origin of the process which ultimately produces the MEJ.
