BACKGROUND The effects of ACE-inhibitors on fibrinolysis are well documented. Experimental and clinical studies have shown that ACE inhibitors induce a reduction in plasma PAI-1 levels in many cardiovascular diseases, like hypertension, coronary heart disease, and heart failure. Their effects on t-PA are more controversial, due to the fact that t-PA exists in several forms, including free and bound to PAI-1. Indeed an increase in t-PA activity has been observed in humans and it seems related to bradykinin increase which is known to stimulate endothelial t-PA synthesis. These favourable effects on fibrinolysis could be related not only to the Angiotensin II reduction and the bradykinin increase but also to the improvement in insulin sensitivity, as insulin has been suggested as one of the main regulators of fibrinolytic activity.

To date conflicting results have been reported about the effects of ARBs on fibrinolysis. Some studies have reported small improvements, others no significant effect. These conflicting results may be due to possible methodological bias but a possible pathophysiological explanation might be that receptor subtypes other than AT1 mediate the effect of Angiotensin-II on endothelial PAI-1 expression, i.e. the AT4 receptors, and during AT1 receptor blockade there is an important increase not only of Angiotensin-II, but also of all its catabolites including Angiotensin IV. The dissimilar effects on of ACE Is and ARBs may also depend on their different action on the RAS and their different effect on insulin sensitivity: ACE-Is improve insulin sensitivity, while the majority of ARBs have been reported to have a neutral effect. Moreover, unlike ACE-Is, ARBs do not affect the metabolism of bradykinin, which is known to stimulate t-PA synthesis and release.

AIM OF THE STUDY The aim of this study is to verify the effect of imidapril compared to candesartan on insulin sensitivity, evaluated through the euglycemic hyperinsulinemic clamp, and on fibrinolysis, evaluated through the plasma PAI-1 and t-PA activity, in mild to moderate hypertensive patients.