Effects of l-NMMA and l-NNA on the Selective ATP-Induced Enhancement of Intratumoral Blood Flow

We studied the effects of N^G-monomethyl-l-arginine (l-NMMA) and N^ω-nitro-l-arginine (l-NNA) on the selective ATP and adenosine-induced enhancement of intratumoral blood flow in rats measured by the hydrogen clearance method. Both adenosine and ATP produced a selective enhancement of the intratumoral blood flow. Neither l-NMMA nor l-NNA had a significant effect on either the CBF or the intratumoral blood flow. Adenosine-induced enhancement was not inhibited by l-NMMA or l-NNA. On the other hand, the ATP-induced enhancement was totally inhibited by both l-NMMA and l-NNA. The inhibitory action of l-NMMA against ATP was blocked by l-arginine, but not by d-arginine. It is suggested that the ATP-induced increase of intratumoral blood flow is evoked by nitric oxide synthesized from the endothelium of the intratumoral blood vessels.