Regulation of purinoceptors in guinea pig pulmonary artery: functional evidences.

In isolated guinea pig pulmonary arteries (precontracted with 1 microM noradrenaline) N6-cyclopentyladenosine (CPA), a selective A1 adenosine receptor agonist, exerted a concentration-dependent contraction, whereas 5'-N-ethylcarboxamidoadenosine (NECA), a non-selective A1/A2 receptor agonist, in the presence of DPCPX (a highly selective A1 receptor antagonist), produced a concentration-related rapid relaxation. Pulmonary arteries obtained from guinea pigs treated with aminophylline (APH) or 8-phenyltheophylline (8-PT) for 10 consecutive days, displayed more pronounced contraction in response to CPA compared to those of solvent-treated animals. Relaxant action of NECA was, however, attenuated in arteries prepared from methylxanthine-treated guinea pigs. Opposite changes were found in vascular tissues excised from chronically dipyridamole(DP)-treated guinea pigs.