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Coxsackievirus B (CB) 4 causes transmural myocarditis in suckling mice with ensuing development of focal ventricular thinning or aneurysms. We studied whether subsequent infection with another cardiotropic virus influences the expression of CB4 disease. CB4 infection was established in 2-day-old CD1 mice by intraperitoneal (IP) inoculation. Three weeks later, surviving animals were randomized to receive CB3 or saline IP. They were then killed over a 45-day period. CB4 neutralizing antibody (NA) titres were comparable in both groups (31 +/- 23 vs 37 +/- 19). CB3 NA were detected in CB3 infected animals only (72 +/- 86 versus 0). The incidence of myocarditis was comparable (67.4% vs 55.2%). The indices of histopathological changes (assessed according to a semiquantitative grading scale from 0-4) were greater among CB3 recipients on day 9 post CB3 challenge (1.38 +/- 0.43 vs 0.46 +/- 0.4, P < 0.001) and to a lesser extent, on day 13 (0.56 +/- 0.56 vs 0.19 +/- 0.38, P > 0.1). On days 30, and 45, these indices became similar in both groups. Focal thinning was noted on days 45 in 6/11 animals with CB4 infection alone and in 0/11 mice with subsequent CB3 infection (P = 0.006). These findings show that CB3 myocarditis can be expressed in mice with prior CB4 disease, that sequential infections do not lead to cumulative cardiac injury, and that subsequent CB3 infection suppresses the formation of CB4 induced ventricular aneurysms.

Objective: To assess the expression of coxsackievirus B3 (CB3) myocarditis in mice with pre-existing CB4 myocardial disease., Design: Double blind comparative study of CB3 myocarditis in CD1 mice with or without prior CB4 induced cardiac damage., Interventions: Antecedent myocardial injury was produced by CB4 infection intraperitoneally at age two days. Two to three weeks later, when CB4 myocarditis was established, infected and control animals were inoculated intraperitoneally with CB3. They were then sacrificed over a 45-day period. Virus and neutralizing antibody titres were measured on days 3 and 13 after CB3 infection, respectively. The incidence of myocarditis and the intensity of histopathological changes (assessed according to a semiquantitative grading scale from 0 to 4) over a 45-day period were compared., Main Results: Among animals with prior CB4 disease, CB3 titres were lower (2.3 +/- 1.7 versus 3.6 +/- 0.8, tissue culture infective dose 50, P = 0.05) and neutralizing antibody response was slightly higher. The incidence of myocarditis was diminished (59.1 versus 89.3%, P = 0.01) and the indices of pathological changes were lower but the differences were not significant (0.68 +/- .54 versus 1.10 +/- 0.20, 1.38 +/- 0.43 versus 1.50 +/- 0.25, 0.56 +/- 0.56 versus 1.26 +/- 0.75, 0.38 +/- 0.58 versus 1.30 +/- 0.78, 0.12 +/- 0.28 versus 0.47 +/- 0.2 on days 3, 9, 13, 30 and 45 post infection, respectively, P > 0.1)., Conclusion: These results demonstrate that prior exposure to CB4 offers some protection from subsequent CB3 infection. Moreover, they show that antecedent CB4 myocardial damage does not predispose to a worsened expression of CB3 myocarditis.

Indomethacin has been shown to increase virus titers and to worsen cardiac injury in the acute phase of coxsackievirus B4 murine myocarditis. The authors evaluated the effects of indomethacin on the histopathologic changes in a later phase of this disease after virus clearance. Two-day old CD1 mice were infected with coxsackievirus B4. Ten days later, surviving animals were randomized to receive indomethacin or saline intraperitoneally for 10 days. They were then euthanatized, and their hearts were examined for the presence of inflammation, necrosis, scarring, and focal thinning. Mortality was slightly higher among treated animals (7/15 versus 2/12, p = 0.3). The index of inflammation (0.6 +/- 0.5 versus 0.7 +/- 0.5) necrosis and scarring (0.4 +/- 0.5 versus 0.3 +/- 0.5) among treated and control animals, respectively, was not significantly different, but the size of involved myocardium (149742 +/- 201982 versus 35300 +/- 45413 microns2) was remarkably larger (p less than 0.05), and focal ventricular thinning (5/12 versus 0/10, p = 0.03) was encountered among indomethacin recipients exclusively. These findings indicate that indomethacin treatment in the late phase of coxsackievirus B4 myocarditis enhances myocardial damage and increases the incidence of focal ventricular thinning.

The effect of captopril on coxsackievirus B3 murine myocarditis was investigated. Thirty-two, 3-week-old mice were infected with coxsackievirus B3 on day 0 of the study, then randomized into a placebo group or a captopril group starting on day 3 of infection. On day 9 of infection, the mice were put to death. Hearts were weighed and processed for light microscopic examination. Heart weight was 125 +/- 19 mg in the control group versus 102 +/- 14 mg in the captopril group (p less than 0.0003). Amount of necrosis as a percentage of left ventricular section was 3.5% (2.0% to 7.5%) in the placebo group versus 2.0% (0.0% to 5.0%) in the captopril group (p less than 0.01). The amount of dystrophic calcification was 5.0% (0.0% to 27.5%) in the placebo group versus 1.3% (0.0% to 20.0%) in the captopril group (p less than 0.01). The extent of the histopathologic involvement by planimetry was 10.2% in the placebo group versus 5.4% in the captopril group (p = 0.052). We conclude that captopril is beneficial in decreasing left ventricular mass and the amount of myocardial necrosis and calcification in the short term in the murine myocarditis model.

The safety of nonsteroidal anti-inflammatory agents in viral infections was assessed in a mouse model of coxsackievirus B4 neonatal myocarditis. Two-day-old mice were infected intraperitoneally with 10(4) TCID50 coxsackievirus B4 and then randomized to receive indomethacin or saline for 7 days. A number of them were killed on designated days. Mortality, viral titers, antibody, and interferon levels plus histopathologic changes in the heart were compared. Among treated animals, mortality was greater (22/45 vs 7/27; p = 0.07) and viral titers were higher on days 4 and 7 (p = 0.038 and 0.028, respectively). Interferon levels were lower on days 4 and 7 (p = 0.028 and 0.008, respectively), and histopathologic changes were more extensive on days 7 and 21 (p = 0.008 and 0.028, respectively). These findings show that indomethacin decreased interferon production, increased coxsackievirus4 titers, and enhanced the virulence of coxsackievirus B4. These results raise significant concerns about the safety of indiscriminate use of nonsteroidal anti-inflammatory agents during severe viral infections.

To date, there is no universally accepted therapy for viral myocarditis. We investigated the effect of the angiotensin converting enzyme inhibitor captopril on both early and late phases of coxsackievirus murine myocarditis. Mice were infected with coxsackievirus B3 and were divided into two main protocols. Mice in the early treatment protocol (n = 30) were treated on day 1 after infection with either captopril or saline through day 6 of infection and euthanized on day 6 of infection. In the late treatment protocol, mice (n = 60) were treated starting on day 10 of infection through day 30 of infection with either captopril or saline. Mice were killed on days 20 and 30 of infection. In the early treatment protocol, heart weight was 67 +/- 14 mg in the captopril-treated group versus 98 +/- 17 mg in the control group (p less than 0.0001). The degree of inflammation, necrosis, and dystrophic calcification assessed with a semiquantitative histological score was significantly less in the captopril-treated group. The degree of pathological involvement determined by planimetry of histological sections was 8.1 +/- 7.2% for the captopril-treated group versus 22.5 +/- 10.0% for the saline-treated group (p less than 0.0001). In the late treatment protocol, captopril also caused a reduction in heart weight as compared with controls at day 20 (116 +/- 21 mg in captopril-treated group vs. 166 +/- 34 mg in controls, p less than 0.0001) and also at day 30 (136 +/- 23 mg in captopril-treated group vs. 185 +/- 48 mg in controls, p less than 0.004). On days 20 and 30 of infection, the degree of inflammation, necrosis, and dystrophic calcification was similar in both groups. We conclude that captopril is beneficial in acute coxsackievirus B3 murine myocarditis because it reduces heart weight and necrosis when administered early and reduces heart weight when administered in a delayed manner.

The effect of salicylates or indomethacin usage during viral infection was investigated in a murine model of coxsackievirus B3 myocarditis. Eighty-two 3-week-old CD1 mice received 3 x 10(5) median tissue culture infective dose (TCID50) of coxsackievirus B3 intraperitoneally. Then they received salicylates, indomethacin, or saline solution daily for 10 days. Mortality, viral and antibody titers, interferon levels, and pathologic changes in the heart were compared. Mortality (2/33, 4/15, and 0/34, respectively) and virus titers (10(4.72), 10(4.78), and 10(3.4) TCID50, respectively) were higher, interferon levels (300, 267, and 980 IU, respectively) were lower, and pathologic changes were worse in treated animals (antibody titers were similar). These findings indicate that nonsteroidal anti-inflammatory agents adversely affect the course of acute coxsackievirus B3 murine myocarditis. Determination of the pathogenesis of this deleterious effect requires thorough evaluation of virus-host interactions.

Previous studies have shown that indomethacin administered during the early phase of experimental myocarditis may exacerbate the disease process. It is unknown whether late administration of this agent is safe. Therefore, the effect of indomethacin administration during the late phase of coxsackievirus B3 murine myocarditis was investigated. Forty 3-week-old CD1 mice each received a 3 x 10(4) median tissue culture-infective dose of coxsackievirus intraperitoneally. On day 10 of infection, mice were randomized to receive either indomethacin or normal saline solution for 10 days, and 10 mice from each group were killed on days 20 and 30 of infection. Heart weight and size and serum atrial natriuretic peptide were similar in both groups on days 20 and 30. On day 20, pathologic scores for the degree of inflammation and necrosis were 1.7 and 1.0 for the indomethacin group versus 1.4 and 1.7 for the saline solution group. On day 30, pathologic scores were 0.3 and 0.6 for the indomethacin group versus 0.5 and 0.6 for the saline solution group. In addition, mineralization was absent in indomethacin-treated animals on day 20 after infection, but it was present in half of the control animals at that time. The degree of mineralization did not differ on day 30 between the two groups. These findings suggest that indomethacin given in the late phase of coxsackievirus myocarditis has no deleterious effects at 30 days.

Recent studies suggest that beta-adrenergic blocking agents show promise in the management of cardiomyopathies; however, their role in acute myocarditis is unknown. One hundred 3 week old mice were infected with coxsackievirus B3 and were given either metoprolol (n = 50) or normal saline solution (n = 50) intraperitoneally for 10 days. Twenty mice from each group were observed for mortality for 30 days. Of the remaining 60 mice, 10 from each group were killed on day 3, 6 or 10 and examined for heart viral titers and pathologic changes. Mortality rate in the metoprolol group was 60% compared with 0% in the saline group (p less than 0.005). Viral titers on day 10 of infection were 10(2.6 +/- 0.2) median tissue culture infective dose for the metoprolol group versus 10(2.1 +/- 0.1) for the saline group (p less than 0.05). Whereas pathologic changes at days 3, 6 and 10 of infection were similar in both groups, on day 30 of infection, inflammation, necrosis and mineralization scores (mean +/- SEM) were 1.1 +/- 0.3, 2.1 +/- 0.4, 2.2 +/- 0.5 for the metoprolol group versus 0.3 +/- 0.1, 0.4 +/- 0.3, 0.4 +/- 0.3 for the saline group, respectively (p less than 0.01). Six noninfected mice received metoprolol intraperitoneally for 10 days; there was no mortality during 30 days of observation. In conclusion, metoprolol administration exerts deleterious effects in acute coxsackievirus B3 murine myocarditis.