Characterisation of angiotensin II receptor mediated responses and inhibition of intimal hyperplasia in experimental vein grafts by the specific angiotensin II receptor inhibitor, L158,809

Objectives: This study characterises pharmacologically the angiotensin II receptor in experimental vein grafts and examines the effect of the angiotensin II receptor (type 1) antagonist (L158,809) on the formation of vein graft intimal hyperplasia in vivo, as well as the in vitro physiological response to angiotensin II of vein grafts after chronic oval L158,809 treatment. Materials: Thirty New Zealand White rabbits had a right carotid interposition bypass graft using the external jugular vein and were killed on the 28th postoperative day. Design: To characterise the angiotensin II receptors, concentration response curves to angiotensin II were obtained in vitro in the presence or absence of L158,809. To determine the effect of L158,809 on the development of intimal hyperplasia, 10 animals received chronic oral therapy with L158,809 (10mg/kg/day; begun 5 days before surgery and continued until harvest) and 10 animals received vehicle only as controls. These grafts were harvested either for histology (n = 6 per group) or for in vitro isometric tension studies to angiotensin II. Results: The monophasic contractile response to angiotensin II in the untreated vein grafts could be inhibited in a concentration dependent manner by L158,809 with first order kinetics. Chronic oval treatment with L158,809 produced a 48% decrease in intimal thickness from 82 ± 1 μm (mean ± S.E.M.) in the controls to 43 ± 7μm in the treated vein grafts (p = 0.002). There was also a significant decrease (45%) in the medial thickness between the control (76 ± 6μm) and L158,809 treated (42 ± 6μm) vein grafts (p = 0.007). The responses to angiotensin II were abolished in the vein grafts by chronic L158,809 therapy. Conclusions: This study suggests that vein graft angiotensin II responses are mediated through a type I receptor and that chronic inhibition with L158,809, significantly reduces intimal hyperplasia and medial hypertrophy in experimental vein grafts and concomitantly abolishes the in vitro responses to angiotensin II. Therefore, angiotensin II acting through AT1 receptors mediates a significant part of the intimal hyperplastic response in vein grafts.