In situ observation of living pericytes in rat retinal capillaries.

We observed the retinal capillary pericytes of the rat in situ. Whole retinae were mounted, immediately post vivo, in a special tissue chamber for electronic light microscopy at high magnifications. Under electronic light microscopy the pericytes could be clearly distinguished from the endothelial cells. In addition, the contractile apparatus of the pericytes was demonstrated by immunohistochemistry with alpha-smooth muscle actin. Administration of angiotensin II as well as endothelin into the observation chamber caused a significant decrease of the mean capillary diameter (13 and 16% reduction, respectively) within 90 s. Carbachol, bradykinin, and histamine significantly increased the capillary diameter within 90 s (13, 20, and 18% increase, respectively). This study demonstrates that our method allows the analysis of vasoactive effects on the retinal capillary in situ. We observed that this type of capillary can actively change its diameter.