Effect of Early vs Late AT1 Receptor Blockade with Losartan on Post-Myocardial Infarction Ventricular Remodeling in Rabbits.

GONZALEZ GE, SEROPIAN IM, KRIEGER ML, PALLEIRO J, LÓPEZ VERRILLI MA, GIRONACCI MM, CAVALLERO S, WILENSKY L, TOMASI VH, GELPI RJ, MORALES C

AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY

AMER PHYSIOLOGICAL SOC

Año: 2009 vol. 297 p. 375 - 386

0363-6135

To characterize the temporal activation of the renin-angiotensin system after myocardial infarction (MI) in rabbits, we examined cardiac ANG II type 1 receptor (AT1R) expression and ANG II levels from 3 h to 35 days. The effects of losartan (12.5 mg/kg-1/day-1) on functional andhistomorphometric parameters when treatment was initiated early (3 h) and late (day 15) post-MI and maintained for different periods of time [short term (4 days), midterm (20 days), and long term (35 days)] were also studied. AT1R expression increased in the MI zone at 15and 35 days (P < 0.05). ANG II levels increased (P < 0.05) in the non-MI zone at 24 h and in the MI zone as well as in plasma at 4 days and then progressively decreased until 35 days. The survival rate was significantly lower in untreated MI and early long-term-treated animals.Diastolic pressure-volume curves in MI at 35 and 56 days shifted to the right (P < 0.05). This shift was even more pronounced in long-term-treated groups (P < 0.05). Contractility decreased (P < 0.05 vs. sham) in the untreated and long-term-treated groups and was attenuated in the midterm-treated group. The early administration of losartan reduced RAM 11-positive macrophages from 4.15  0.05 to 3.05 0.02 cells/high-power field (HPF; P < 0.05) and CD45 RO-positive lymphocytes from 2.23 0.05 to 1.48 0.01 cells/HPF (P 0.05) in the MI zone at 4 days. Long-term treatment reduced the scar collagen (MI: 70.50 2.35% and MI losartan: 57.50 2.48, P < 0.05), determined the persistency of RAM 11-positive macrophages (3.02 0.13 cells/HPF) and CD45 RO-positive lymphocytes (2.77 0.58 cells/HPF, P < 0.05 vs. MI), and reduced the scar thinning ratio at 35 days (P < 0.05).  Consequently, the temporal expressions of cardiac AT1R and ANG II post-MI in rabbits are different from those described in other species. Long-term treatment unfavorably modified post-MI remodeling, whereas midterm treatment attenuated this harmful effect. The delay in wound healing (early reduction and late persistency of inflammatory infiltrate) and adverse remodeling observed in long-term-treated animals might explain the unfavorable effect observed in rabbits.