Systemic hypertension produces pericyte changes in retinal capillaries

Purpose. The purpose of this study was to examine retinal capillaries and their pericytes that previous research suggests to be contractile. A contractile role regulating capillary blood flow may be more apparent when the vasculature is subjected to the stress of systemic hypertension. Methods. Using ultrastructural morphometry and the myosin subfragment-1 technique, retinal capillaries of normal and hypertensive rats were measured at three different time points, early, intermediate, and late (24, 44, and 68 wk). Results. Hypertensive capillaries seemed to dilate at the early time point (P = 0.002), were constricted at the intermediate time point (P < 0.001), and did not redilate later. Wall thickness was enlarged at all times, pericyte coverage (the ratio of plasma membrane length in contact with the vascular circumference to the outer circumference of the endothelial tube) was greater at early and intermediate time points, and the total area of viable cytoplasm relative to the vessel wall area was increased at the intermediate time (all P < 0.001). Also, at the intermediate time, the circumferential coverage of the endothelial tube by actin filament bundles within pericytes and the actin area relative to the vessel wall area had increased (P < 0.001). Conclusions. These data indicate that the effects of systemic hypertension extend into the retinal capillary bed, causing pericyte change with actin increase and capillary constriction. They represent the first in vivo indirect evidence by morphologic criteria for pericyte contractility in retinal vascular disease.