FURTHER EVIDENCE THAT PROPENTOFYLLINE (HWA-285) INFLUENCES BOTH ADENOSINE RECEPTORS AND ADENOSINE TRANSPORT

We have examined the actions of a novel xanthine derivative, propentofylline (HWA 285), that has been shown to protect against ischemic brain damage in rats and gerbils, on adenosine receptors (A, and A2), and on adenosine transporters using several techniques, cells and tissues. Propentofylline and its hydroxylated metabolite A 72 0287 were about 20 times less potent than theophylline in displacing A1-agonist binding to membranes from rat cortex, and A1-antagonist binding to whole DDT, MF-2 smooth muscle cells. A1-agonist binding to adenosine A1-receptors in several brain structures was inhibited in a concentration-dependent manner by A 72 0287 and propentofylline as judged by quantitative autoradiography (IC50-values 300-600-mu-M in eg striatum and in cortex layer IV). In two functional assays, A1-receptor mediated effects were blocked by propentofylline. A1-receptor-mediated inhibition of cyclic AMP accumulation was virtually abolished by 100-mu-M propentofylline. The A1-receptor-mediated inhibition of evoked acetylcholine release was also reduced by propentofylline, but in this case the effect is not due exclusively to adenosine receptor antagonism but also to another action since the presynaptic inhibitory effect of carbachol was also inhibited. Adenosine A2-receptors were also antagonized by propentofylline as; judged by a concentration-dependent antagonism of A1-agonist-induced cAMP accumulation in human T-leukemia cells (possessing putative A2b-receptors; pA2-value 180-mu-M compared to 0.26-mu-M for 8-cpt), and in PC-12 cells (possessing putative A2a-receptors, K(i)-value 365-mu-M). Finally, adenosine transporters were affected by propentofylline and A 72 0287. Thus, [H-3]-nitrobenzylthioinosine-binding to guinea-pig cardiac membranes was blocked by propentofylline or A 72 0287 (K(i) 270-mu-M). The present results show that propentofylline and its hydroxylated metabolite can influence adenosine mechanisms in a multitude of ways. How these different actions may contribute to the ability of propentofylline to reduce the magnitude of ischemic damage is discussed.