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 chamb er for electronic light microscopy at high magnifications. Under elect ronic light microscopy the pericytes could be clearly distinguished fr om the endothelial cells. In addition, the contractile apparatus of th e 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 capil lary diameter within 90 s (13, 20, and 18% increase, respectively). Th is study demonstrates that our method allows the analysis of vasoactiv e effects on the retinal capillary in situ. We observed that this type of capillary can actively change its diameter. (C) 1998 Academic Pres s.