Maintenance of renal autoregulation during infusion of aminophylline or adenosine

Adenosine has been postulated to link control of glomerular filtration rate (GFR) and renal blood flow (RBF) with changes in renal metabolism. In the present study, we examined the role of adenosine in renal autoregulation by comparing the responses of normal anesthetized dogs to step decreases in renal artery pressure (RAP) to the response obtained after receptor blockade of adenosine with aminophylline or by flooding the kidney with exogenous adenosine. In six dogs at normal RAP, intrarenal infusion of aminophylline (10 μmol/min) did not alter renal hemodynamics. GFR and RBF were well autoregulated (>90% of control) at RAP values equal to or greater than 85 mmHg before and after aminophylline. At RAP equal to 75 mmHg, GFR and RBF decreased by 27 ± 10 and 20 ± 8%, respectively, before aminophylline and by 25 ± 7 and 13 ± 6% after aminophylline. In a different group of six dogs, intrarenal infusion of adenosine (6 μmol/min) significantly increased RBF (32 ± 9%) and decreased GFR (38 ± 10%) at normal RAP. However, GFR and RBF were both well autoregulated (>90% of control) at RAP values equal to or greater than 85 mmHg before and after adenosine. At RAP equal to 75 mmHg, GFR and RBF decreased by 10 ± 5 and 7 ± 3%, respectively, before adensoine and by 12 ± 6 and 17 ± 5% after adenosine. Neither aminophylline nor adenosine attenuated the elevations in plasma renin activity associated with reductions in RAP. These data fail to provide evidence that adenosine is an important factor in autoregulation of GFR and RBF during acute reductions in RAP within the autoregulatory range.