Impaired blood flow autoregulation in nonfiltering kidneys: effects of theophylline administration

To investigate blood flow autoregulation in filtering and nonfiltering kidneys, renal blood flow was determined during graded reductions in renal perfusion pressure in seven anesthetized dogs containing both a filtering and nonfiltering kidney. In each dog, one kidney was made nonfiltering by the method of EH Blaine, JO Davis, and RT Witty (Circ Res 27:1081-1089, 1970). Renal perfusion pressure was decreased from 129 to 115, 99, and 83 mm Hg by stepwise constriction of the suprarenal aorta. In filtering kidneys, the maximum decrease in renal perfusion pressure reduced renal blood flow only 20.1% of control whereas renal blood flow of nonfiltering kidneys decreased by 41.0% of control. During aortic constriction, renal vascular resistance of nonfiltering kidneys remained unchanged or slightly increased. These hemodynamic changes were associated with significantly greater autoregulation indices in nonfiltering kidneys. In eight dogs with nonfiltering kidneys, competitive inhibition of adenosine with theophylline (9 mg/kg iv) restored autoregulation of renal blood flow as shown by significant decreases in renal vascular resistance. These data indicate that in the nonfiltering kidney model, autoregulation of renal blood flow is impaired. It is suggested that this impaired autoregulatory response may result from renal ischemia and the vasoconstrictor influence of elevated intrarenal adenosine concentration.