The kidney expresses all and independently regulates most elements of the renin-angiotensin system (RAS). Importantly, the inappropriate activation of intrarenal RAS, as indicated by the local accumulation of angiotensin II (Ang II), has been linked to Ang II-induced hypertension. Various Ang II and angiotensin type 1 receptor (AT1R)-dependent positive feedback systems have been documented in the literature. However, their functional importance to the overactivation of the intrarenal RAS have yet to be lineated. The goal of this study is to identify the key mechanisms actuating the intrarenal accumulation of Ang II during hypertension induced by Ang II infusion. We hypothesize that the upregulation of tubular epithelial AT1Rs is the primary mediator of intrarenal RAS overactivation following Ang II infusion. To test this hypothesis, computational models of the intrarenal RAS and the AT1R-blocker Losartan were created, coupled, and used to simulate Ang II-infusion experiments in the absence and presence of this anti-hypertensive therapy. Model simulations indicate that total renal Ang II concentrations rise once Ang II starts accumulating within tubular epithelial cells and that the upregulation of local AT1R expression, not Ang II production, is required to produce this effect. Indeed, the removal of this positive feedback and the administration of Losartan both prevented the intrarenal accumulation of Ang II. Since the simulated onset of Ang II accumulation in tubular epithelial cells coincides exactly with the experimental inception of Ang II-dependent hypertension, we conclude that the stimulation of sodium reabsorption mediated by local Ang II is likely key to the development of Ang II-induced hypertension.
Support or Funding Information
This research is supported in part by the Canada 150 Research Chair program, a Natural Sciences and Engineering Research Council of Canada (NSERC) Discoveryaward, and a Canadian Institutes of Health Research (CIHR) award.
