Increases in the local flow of blood through microvessels in response to an increased tissue metabolism play an important physiological role in supplying additional nutrients and removing excess waste at the cellular level. Control of this supply and demand phenomenon has been attributed to the smallest and terminal arterioles. However, if these arterioles were the only ones to dilate in response to increased tissue metabolism, their blood flow might actually decrease due to the overall increase in their total cross-sectional area. In order to increase blood flow to tahe tissue the larger diameter arterioles (site of greatest resistance to blood flow) must also dilate. This mechanism by which the metabolic status of tissue is communicated to these larger arterioles is poorly understood. Therefore, the primary goal of this research program is to delineate the mechanism by which larger arterioles may participate in the metabolic regulation of local blood flow. The overall hypothesis to be examined is that large venules respond to tissue metabolite and/or lack of nutrients by releasing vasoactive factors that produce the dilation of nearby arterioles. Four specific hypotheses will be examined; 1. that endothelium-derived relaxing factor/nitric oxide (EDRF/NO) can be released from and dilate large arterioles in response to application of tissue metabolites; 2. that EDRF/NO can be released from large venules in response to the application of tissue metabolites; 3. that venular -derived EDRF/NO can both activate the release of arteriolar-derived EDRF/NO and produce arteriolar dilation under in vitro conditions; and 4. that venular-stimulated release of EDRF/NO by tissue metabolites can produce vasodilation in nearby arterioles in vivo. A combination of isolated microvessel and fluorescent digital image analysis techniques will be used to investigate these hypotheses both in vitro and in vivo. An important component of these studies will be to delineate the relationship between increases in endothelial cell calcium and EDRF/NO synthesis and release. Knowledge of the coordinating pathways involved in transmitting tissue metabolic signals to upstream resistance vessels will enable us to more fully understand blood flow autoregulation and will provide insight into mechanisms which underlie arteriolar vasomotor tone. In addition, understanding these basic mechanisms will assist in interpreting the role of metabolic vascular control in the vascular pathology associated with disease stats such as hypertension, diabetic microangiopathy and cancer. Further advances could be used to identify sites for novel and specific pharmacological intervention.
