[Assessment of the Bezold-Jarisch reflex in experimental myocardial infarction]

To evaluate the cardiogenic depressor Bezold-Jarisch reflex in rats with chronic myocardial infarction.

Adult Wistar rats were submitted to ligation of the anterior descending coronary artery of the left ventricle (group INF, n = 15) and compared with rats submitted to sham-operation (group Sham, n = 15). Thirty days after the surgery, without influence of anesthetics, the basal mean arterial pressure (MAP) and heart rate (HR) were measured. Immediately after, the Bezold-Jarisch reflex was evaluated measuring the falls in diastolic arterial pressure (DAP) and the simultaneous bradycardia induced by injections of 5-hydroxytryptamine (5-HT, 4 to 32 micrograms/kg, i.v.).

The INF group showed significantly lower basal MAP and HR values (103 +/- 3 mmHg and 328 +/- 6 bpm) when compared to the Sham group (110 +/- 2 mmHg and 348 +/- 7 bpm). The Bezold-Jarisch reflex was significantly attenuated in the INF group (falls of DAP from 2 +/- 2 to 31 +/- 3 mmHg and HR from 8 +/- 5 to 204 +/- 15 bpm), when compared to the Sham group (falls of DAP from 10 +/- 3 to 41 +/- 3 mmHg and HR from 58 +/- 12 to 276 +/- 16 bpm). The morphological analysis showed a myocardial infarction mainly located at the anterolateral portion of the left ventricle with a maximal extension of 35% of the left ventricle circumference. The INF group showed right ventricular and left atrial hypertrophy when compared to the Sham group.

The experimental chronic myocardial infarction in rats is followed by significant attenuation of the Bezold-Jarisch reflex, probably as result of a heart failure and, consequently, of functional alterations in the chemosensitive receptors of cardiac unmyelinated vagal afferents.