Effects of prednisolone on acute viral myocarditis in mice

The effect of prednisolone on viral myocarditis was studied in BALB/c mice with encephalomyocarditis virus myocarditis. Prednisolone was injected intramuscularly, 10 mg/kg once a day, on days 4 to 13 (experiment 1) and on days 8 to 17 (experiment 2). The control mice in each experiment received injections of distilled water. In experiment 1, myocardial virus titers were maximal but neutralizing antibodies were rarely present on day 4, and viral titers were still elevated and antibody titers were high on day 8. The survival rate of the prednisolone group was significantly lower (p less than 0.05) than that of the control group on days 21, 22 and 23. On day 10, the antibody titers of the prednisolone group were significantly lower (p less than 0.01) than those of the control group, and viral titers of the prednisolone group remained significantly elevated (p less than 0.01), whereas viruses were rarely isolated in the control group. In experiment 2, the survival rate and antibody titers were not significantly different in the prednisolone and control groups. In both experiments, no viruses were isolated on day 14. The present study suggests that corticosteroids given in the early stage aggravate the course of acute viral myocarditis, and that they may not have detrimental effects if given when neutralizing antibody titer levels are high, although they are not expected to have a beneficial effect.