1. The aim of the present study was to evaluate the effect of treatment with
enalapril on the sensitivity of cardiopulmonary reflexes 30 days after
myocardial infarction in Wistar rats. 2. Animals were divided into four groups: (i)
sham operated, receiving vehicle (
SHAM); (ii) infarcted, receiving vehicle (
0.9% NaCl; INF); (iii)
sham operated, receiving
enalapril (SHAME); and (iv) infarcted, receiving
enalapril (INFE). 3.
Enalapril was administered at a dose of 10 mg/kg per day.
Serotonin (4-32 microg/kg, i.v.) was administered in order to activate the Bezold-Jarisch reflex, which was estimated as the percentage of reduction in heart rate. 4. The volume-sensitive cardiopulmonary reflex was induced by saline overload and evaluated as the percentage increase in
sodium and volume renal excretion. At the end of the experiments, rats were killed and hearts excised to estimate the size of the
infarction. The weight of the kidneys, lungs, liver and cardiac chambers as ratios of bodyweight was used to estimate the extent of
hypertrophy. 5. The results showed an impairment in the sensitivity of the cardiopulmonary reflexes in the INF group compared with the
SHAM and SHAME groups. We observed right ventricle and pulmonary
hypertrophy, a reduction in mean and systolic arterial pressure and an increase in heart rate in INF animals. In the INFE group, nearly all the parameters were normal compared with the INF group, except for systolic arterial pressure, which was only partially improved. 6. The main finding of the present study was that treatment with
enalapril normalized the sensitivity of the cardiopulmonary reflexes, which could be due, in part, to the reduction of
cardiac hypertrophy. The present study provides information about the beneficial effects of the
angiotensin-converting enzyme inhibitors by normalizing the cardiopulmonary reflexes involved with the regulation of volume and
sodium, as well as control of arterial pressure and heart rate in infarcted animals.