HEART-RATE RESPONSES TO INTRAVENOUS SEROTONIN IN RATS WITH ACUTE CHAGASIC MYOCARDITIS

We administered serotonin to rats with experimentally induced chagasic myocarditis in order to study the Bezold-Jarisch reflex. Sixteen 4-mo nth old Wistar rats were inoculated with 200,000 T. cruzi parasites (' 'Y'' strain). Between days 18 and 21 (acute stage), 8 infected rats an d 8 age-matched controls received intravenous serotonin as a bolus inj ection at the following doses: 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0, 12. 0, and 14.0 mu g/kg. Heart rate was recorded before, during and after each dose of serotonin. The remaining 8 infected animals and 8 control s were subjected to the same experimental procedure during the subacut e stage, i.e., days 60 to 70 after inoculation. The baseline heart rat e of the infected animals studied during the acute stage (327 +/- 62 b eats/min, mean +/- SD) was higher than that of the controls (248 +/- 5 2, P<0.01). The heart rate changes were expressed as percent changes t o correct for the higher baseline heart rate of the infected animals. A dose-response curve was constructed for each group of animals. The d ope for the acutely infected animals (r = -0.95, b = -3.98) was not di fferent from that for the control animals (r = -0.92, b = -3.50). The infected animals studied during the subacute stage (r = -0.92, b = -4. 33) were not different from the age-matched controls (r = -0.87, b = - 4.03). These results suggest that the afferent and efferent pathways w hich mediate the Bezold-Jarisch reflex are functionally preserved in r ats with histologically proved chagasic myocarditis.