Angiotensin II (ANGII) can elicit renal vasoconstriction through effects on both afferent (AFF) and efferent (EFF) arterioles; however, these vasoconstrictor responses are variably expressed both in vivo and in vitro, indicating that some poorly-defined factor(s) determine whether ANGII elicits vasoconstriction at pre-and/or postglomerular sites. The overall goal of this project is to provide specific information regarding the mechanisms through which ANGII influences renal microvascular resistance. The project is comprised of two general areas of emphasis. The first involves an analysis of integrative factors which might influence the vasoconstrictive influence of ANGII on specific segments of the renal microvascular network. The in vitro blood-perfused juxtamedullary nephron technique will be exploited to achieve direct microvascular access while preserving the anatomical and functional interrelationships between tubular and vascular components of the nephrovascular unit. We will determine the extent to which AFF and EFF responses to ANGII are influenced by the modulatory effects of endothelium-derived relaxing factor (EDRF). We will also determine the contribution of outer medullary descending vasa recta (DVR) resistance alteration to the postglomerular actions of ANGII and arginine vasopressin. We will examine the ability of these peptides to alter DVR diameter, either directly or secondary to the arteriolar effects of the agents, and will assess the modulatory influences of arachidonic acid metabolites and EDRF at this site. The second area of emphasis involves characterization of intracellular signaling events evoked by ANGII, testing the hypothesis that these differ at AFF and EFF arteriolar sites. Isolated AFF and EFF arterioles will be studied in vitro, allowing videometric monitoring of diameter responses as well as dual excitation wavelength spectrofluorometric analysis of intracellular ion concentrations and membrane potential. We will determine whether or not AFF and EFF arteriolar responses to ANGII differ with regard to Ca2+ entry requirements, the role and origin of depolarization, and the roles of IP3-and protein kinase C-dependent processes. It is anticipated that these studies will reveal functionally relevant distinctions between the determinants of ANGII's effects on pre-and postglomerular vascular segments, as well as providing further information regarding hormonal interactions in the regulation of vascular resistance by discrete segments of the renal microcirculatory network.
