To reveal the role of enzymes involved in PGI2 synthesis for vascular PGI2 generation in experimental hypertensive models, we defined PGI2 synthase and phospholipases activities in the aortic wall of two different experimental hypertensive rats, e.g. spontaneously hypertensive rats (SHR) and desoxycorticosterone acetate (DOCA)-salt hypertensive rats. In the stage of established hypertension both of the hypertensive models had a significantly large capacity of the vascular wall to produce PGI2, as compared to respective control rats. PGI2 synthase activities in the vascular wall were significantly increased by 27% for SHR and by 80% for DOCA-salt hypertensive rats. Moreover, the enzymatic activities were closely related to the blood pressure values for both of the models. On the other hand, phospholipase C or phospholipase A2 activities were increased or unchanged in SHR, respectively, whereas both of the phospholipases were significantly decreased in DOCA-salt hypertensive rats. Thus, it is indicated that PGI2 synthase is partly responsible for the increased PGI2 generation in the vascular wall of SHR and DOCA-salt hypertensive rats, and that vascular phospholipase C is playing a more important role in providing arachidonate for PGI2 synthesis in SHR.