Renal Interstitial ATP Responses to Changes in Arterial Pressure During Alterations in Tubuloglomerular Feedback Activity

Abstract

P90 We have recently demonstrated a direct relationship between autoregulatory related changes in renal vascular resistance (RVR) and changes in renal interstitial ATP levels. To examine further the possible role for extracellular ATP in the regulation of tubuloglomerular feedback (TGF)-mediated autoregulatory adjustments in RVR, experiments were performed in 8 anesthetized dogs to assess interstitial ATP concentrations in response to changes in renal arterial pressure (RAP) during augmented and diminished activity of the TGF mechanism. Using a microdialysis method, interstitial ATP levels were assessed at different levels of RAP before and during intra-arterial administration of acetazolamide (ACZ; 100 μg/kg/min, n=4) which increases solute delivery to the macula densa thus augmenting TGF activity, and after furosemide treatment (10 μg/kg/min, n=4) which inactivates the TGF mechanism. During the control period, stepwise reductions in RAP within the autoregulatory range from ambient pressure (126±4 mmHg) to 100±2 mmHg (step-1: S1) and 76±2 mmHg (step-2: S2) resulted in significant decreases in ATP concentrations from 8.9±0.7 to 6.3±0.6 nM (S1) and 4.0±0.5 nM (S2). ACZ decreased renal blood flow (RBF; -22±6%) and glomerular filtration rate (GFR; -28±4%), and increased RVR (22±2%) and ATP concentrations (7.9±0.9 to 14.3±1.8 nM). During ACZ infusion, the autoregulatory efficiency of RBF and GFR were maintained, and ATP levels were significantly decreased in responses to reductions in RAP (8.8±0.8 nM in S1 and 6.5±0.7 nM in S2). Inhibition of the TGF mechanism by furosemide increased RBF (32±9%) and GFR (17±2%), and decreased RVR (25±6%); ATP levels concentrations decreased from 8.7±1.1 to 5.4±0.9 nM. Furosemide caused marked impairment of RBF and GFR autoregulatory efficiency (by -17±3 and -16±6% in S1 and by -31±5 and -23±7% in S2, respectively). In addition, pressure-induced changes in ATP levels were completely prevented by furosemide (5.3±0.4 nM in S1 and 5.5±0.5 nM in S2). These data support the hypothesis that extracellular ATP contributes to the RVR adjustments that are elicited by changes in activity of the TGF mechanism.