To measure the effect of hypertension on neointima formation after balloon injury of rat aorta and its association with the local angiotensin converting enzyme (AcE) concentration. Balloon angioplasty of the thoracic aorta using a 2 French Fogarty catheter was performed in spontaneously hypertensive rats (SHR) and normotensive Sprague-Dawley (SD) rats.
The uninjured aortic wall of SHR had already significantly higher ACE concentrations than did the uninjured aortic wall of normotensive SD rats (media: 729 ± 37 dpm/mm2 in SHR versus 496 ± 38 dpm/mm2 in SD rats, P < 0.01; intima: 83 ± 5 dpm/mm2 versus 68 ± 6 dpm/mm2 in SD rats, P < 0.01). Fourteen days after injury of the aorta the hypertensive rats had significantly higher neointima : media ratios than did the normotensive rats (0.83 ± 0.09 versus 068 ± 0.01, P < 0.01). This was associated with a significant increase in vascular media and neointima ACE concentrations in SHR (media 965 ± 25 dpm/mm2, neointima 614 ± 48 dpm/mm2) compared with those in normotensive SD rats after balloon angioplasty (media 669 ± 23 dpm/mm2, neointima 287 ± 33 dpm/mm2, P < 0.01). ACE inhibitor treatment with 10 mg/kg body weight lisinopril daily for 14 days by gavage reduced neointima proliferation in hypertensive and normotensive rats (neointima : media ratio: 0.35 ± 0.02 for SHR, P < 0.01, versus untreated SHR with balloon injury; 0.28 ± 0.01 for SD, P < 0.01, versus untreated SD rats with balloon injury). This was associated with significant vascular media ACE inhibition (SHR 149 ± 9 dpm/mm2; SD rats 118 ± 7 dpm/mm2; P < 0.01, versus untreated controls with balloon injury) and neointima ACE inhibition (SHR 73 ± 4 dpm/mm2, SD rats 63 ± 7 dpm/mm2, P < 0.01, versus untreated controls with balloon injury), but also lowered the blood pressure in SHR significantly (to 148 ± 5 mmHg, P < 0.01, versus untreated SHR with balloon injury). When this drop in blood pressure was prevented by feeding the rats a high-salt diet (SHR with ACE inhibitor plus high salt-diet group blood pressure 193 ± 3 mmHg, P = 0.57, versus untreated SHR) hypertension per se without the local ACE increase (ACE concentration in SHR with ACE inhibitor plus high-salt diet rats' media 167 ± 10 dpm/mm2 and neointima 81 ± 9 dpm/mm2) had only a mild effect on neointima formation after balloon angioplasty (neointima : media ratio 0.4 ± 0.01 for SHR with ACE inhibitor plus high-salt diet versus 0.35 ± 0.02 for SHR with ACE inhibitor plus normal-salt diet, P < 0.05). Treatment with 10 mg/kg body weight angiotensin II subtype 1 receptor antagonist losartan potassium daily for 14 days by gavage was associated with a reduction in neointima formation similar to that observed with the ACE inhibitor both for SHR and for SD rats (neointima : media ratio 0.32 ± 0.04 for SHR with losartan, 0.27 ± 0.03 for SD rats with losartan; P < 0.01, versus untreated controls with balloon injury) suggesting that ACE inhibition prevented neointima formation, at least in part, by reducing the local production of angiotensin II.
Neointima formation after balloon angioplasty in SHR is increased compared with that in normotensive SD rats. This is due mainly to there being a higher degree of activation of the renin-angiotensin system in the aorta of the SHR before and after balloon injury compared with that in normotensive SD rats measured in terms of the increased vascular ACE concentrations. Blood pressure alone had only a moderate effect on neointima formation.