Influence of adenosine receptor blockade on renal function and renal autoregulation

Experiments were conducted in anesthetized dogs to evaluate the effects of adenosine receptor blockade on renal function and on autoregulation of total RBF and outer cortical blood flow. After control measurements, the adenosine receptor antagonist, 1,3-dipropyl-8-p-sulfophenylxanthine (PSPX) was infused intrarenally for 45 min at 2 or 6 microM/min. Responses to PSPX were compared with those obtained during infusions of either aminophylline or theophylline. PSPX infusion led to substantial increases in urine flow and sodium excretion (four- to fivefold). RBF increased significantly; however, outer cortical blood flow and GFR were not significantly altered. PRA increased twofold during PSPX infusion. The vasoconstrictor responses to bolus injections of 2-chloroadenosine (100 mumol) were attenuated by 58 and 86% during the low and high doses of PSPX and to a lesser extent with aminophylline/theophylline infusions. At renal arterial pressures above the inflection point, the slope of the average pressure-flow relationship during PSPX infusion was close to zero and was not significantly different from control. Similarly, autoregulatory capability was not altered during infusions of theophylline or aminophylline. These data provide further evidence that endogenous adenosine contributes substantially to the control of renin release but only modestly to the control of RBF and GFR and to renal autoregulatory capability. The natriuretic responses during adenosine blockade, which occurred in the face of elevated renin levels, support the hypothesis that endogenous adenosine enhances tubular sodium reabsorption rate.