UC San Diego

Extensive evidence displays that vascular endothelium from arteries and veins respond to fluid shear stress. But the fluid shear response in capillary endothelium is unexplored. In this thesis, I hypothesize that the capillary endothelium can control capillary network velocity through modification of individual capillary dimensions in a shear stress-dependent mechanism. The effect of the hypothetical capillary-level control is a capillary network that exhibits similar perfusion velocities inside each capillary despite heterogeneity in capillary length, diameter, and network connectivity. I developed a new method to determine red cell velocity simultaneously in all the capillaries of a capillary network by utilizing intravital microscopy and state-of- the-art imaging software. A highly sensitive camera recorded the passage of fluorescently labeled blood cells through the capillaries and this information is processed to determine capillary velocity. I investigated the effect of topology and rheology on capillary network velocity in control tissue. I found that rheology does not appear to contribute significant variation to the overall capillary network velocity variation. Topological effects may create the baseline heterogeneity. Any system for control of topology may cause modified capillary velocity variation. I investigated the involvement of shear-sensitive aspects of endothelial structure and function in a capillary velocity control system. I examined the contributions of nitric oxide signaling and the endothelial glycocalyx to the maintenance of capillary hemodynamics. These particular components of endothelial signaling pathways have been shown to affect the endothelial fluid shear response. Nitric oxide attenuation caused an elevation of capillary velocity variation, while enzymatic reduction of the glycocalyx reduced the variation. The studies served to determine that capillary endothelium may be capable of sensing and responding to local shear-stresses. I applied the analysis outlined above to the specific endothelial dysfunction in a chronic hypertension model. Disruption of nitric oxide signaling and glycocalyx have been previously determined in hypertension, but a functional relationship to perfusion homeostasis and capillary network resistance has not been established. Herein I measure velocity in distinct capillaries of the same network to study the effects of endothelial dysfunction intrinsic to hypertension on capillary network perfusion