Objective: The aim was to study the effect of the AT1 receptor antagonist losartan on hemodynamic and morphometric changes following experimental infarction.
Methods: Experimental infarction was produced in adult male rats by ligating the coronary artery. Treatment with losartan was compared to untreated controls, in rats with experimental infarction and sham-operated animals.
Results: Infarcted hearts were characterized by significant decreases in left ventricular developed pressure, as well as positive and negative (dP/dt)max, whereas left ventricular end-diastolic pressure (LVEDP), relaxation constant tau and right ventricular systolic pressure (RVSP) significantly increased. Treatment with losartan decreased the LVEDP, the relaxation constant tau and RVSP in the infarcted hearts. Right ventricular weight significantly increased in rats with infarction; this was attenuated by losartan. Infarct size was not significantly influenced by losartan treatment. Morphometric data revealed decreased capillary supply in infarcted hearts, especially in regions close to infarction; the decrease was less pronounced after losartan treatment. Capillary density in near infarct region decreased from 2826/mm2 to 1471/mm2 in untreated animals but in the treated animals it decreased from 2982/mm2 to only 2037/mm2. Simultaneous significant decrease in myocyte-to-capillary ratio in treated animals compared to untreated rats (0.87 to 0.67) seems to indicate formation of new capillary channels after losartan treatment. LVEDP was dependent on the size of infarction in untreated but not in treated animals. A close correlation between LVEDP and capillary density was found.
Conclusions: Decreased ventricular contractility, prolonged relaxation and decreased coronary capillary density in rat experimental cardiac infarction confirm and amplify previous reports dealing with this experimental model. Moreover, we have found evidence of improved hemodynamics and coronary angiogenesis after losartan treatment.