Abstract
Drugs were administered to anesthetized dogs directly into the left renal artery perfused with animal's own blood at a constant pressure. A single injection of adenosine caused prompt renal vasoconstriction, while an infusion of adenosine caused initial vasoconstriction which recovered to the control level even though infusion was continued. The vasoconstriction caused by a single injection of adenosine was not only depressed but also reverted to vasodilation during infusion of adenosine in its concentration from 8×10-9 to 8×10-6g/ml in the perfused blood (self-inhibition), while norepinephrine-induced vasoconstriction was significantly enhanced in the concentration as low as 3×10-9g/ml of adenosine. The vasoconstriction caused by stimulation of renal periarterial nerve fibers was also significantly potentiated. These changes in responses disappeared promptly after interruption of adenosine infusion. Infusion of AMP acted similarly to adenosine but the effects were less. Infusion of ADP and ATP also depressed the effect of adenosine while the potentiation of the effect of norepinephrine was less during ADP infusion and absent during ATP infusion. Adenosine or AMP probably plays an important role in regulation of blood flow by modulating the adrenergic mechanism in the renal circulation.
