In SHR aorta, prostacyclin is an endothelium-derived contracting factor contributing to the endothelial dysfunction. This study was designed to determine whether the impairment of the prostacyclin response is influenced by aging and whether such a dysfunction is observed in platelets. Isometric tension was measured in aortic rings and aggregation was studied in platelet-rich plasma taken from 3, 6 and 15 month-old WKY and SHR. In aorta from 3 and 6 month-old WKY, prostacyclin and beraprost (IP receptor agonists) produced relaxations that were enhanced by Triplion® (TP-receptor antagonist). In 15 month-old WKY, the relaxations to beraprost were maintained, but not those to prostacyclin. In SHR aorta, prostacyclin or beraprost produced no or minor relaxations, which, in younger SHR, were enhanced by Triplion . In both strains, the relaxations were inhibited by CAY-10441 (IP-receptor antagonist). The relaxations to forskolin and isoproterenol were reduced with aging. When compared to WKY, the relaxations to isoproterenol were reduced in 3 but not in 6 or 15 month-old SHR, whereas those to forskolin were consistently diminished at any given age. Whatever the age, prostacyclin and beraprost produced CAY-10441-sensitive inhibitions of ADP-induced platelet aggregation. Both agonists were more potent in SHR than in WKY. Therefore, in platelets from WKY and SHR the IP-receptor-dependent antiagregant response is functional and maintained during aging. In aorta from WKY those responses are reduced by aging and, in SHR, are already compromised at 3 months. This dysfunction of the IP-receptor is only partially explained by a general dysfunction of the adenylate-cyclase pathway.