Purpose:To study the effects of benzodiazepine midazolam in the coronary flow (Cflo), cardiac frequency (CF) and myocardial contractility in isolated hearts of rats subjected to ischemic preconditioning (IPC). Methods: 30 Wistar rats were used, undistinguished by gender. After anesthesia with ethyl ether, the hearts were put into perfusion (Krebs-Henseleit solution, 95% O 2 and 5% CO 2 , 37°C, 110-120mmHg), in disposable Langendorff type system. Five groups of six animals were constituted: GI-Control; GII-Ischemia; GIII-IPC; GIV-Ischemia + 100mcg of midazolam; GV-IPC + 100mcg of midazolam. After stabilization (t 0 ), and on times t 5 , t 10 , t 15 , t 20 and t 25 , CF, Cflo, systolic pressure (SP) and diastolic pressure (DP) and dP/dt were recorded. DP was maintained at 5 ± 2 mmHg. The statistical method ANOVA and Tukey Test were employed for p < 0.05. Results: No significant variations have occurred between Cflo and CF. On Pd/td, differences have occurred (p<0.05) between groups I and II (respectively 94.7±23.0 and 62.3±12.1%). The preconditioning (GIII), improved significantly the results in the group II (respectively 62.3±12.1 and 87.1±12.4 %). The decrease in dP/dt in group II was not prevented by midazolam (GIV) (62.3±12,1 and 60.5±15.8 %). In group III, dP/dt was 87.1±12.4%, whereas in group V, only 55.5±17.2% (p<0.05) Conclusion: Midazolam, when administered before the ischemia, was unable to prevent the ischemic deterioration of the myocardium. When administered before the preconditioning, it has abolished its protective effect. Key words: Ischemic Preconditioning. Heart. Midazolam. Rats. RESUMOObjetivo: Estudar os efeitos do benzodiazepínico midazolam no fluxo coronariano (Fco), freqüência cardíaca (FC) e contratilidade miocárdica de corações isolados de ratos submetidos ao precondicionamento isquêmico (PCI). Métodos: Foram utilizados 30 ratos Wistar sem distinção de sexo. Após anestesia com éter etílico, os corações foram postos em perfusão (solução de Krebs-Henseleit, 95% de O 2 e 5% de CO 2 , 37°C, 110-120mmHg), em sistema tipo Langendorff descartável. Foram constituídos cinco grupos de seis animais: GI-Controle; GII-Isquemia; GIII-PCI; GIV-Isquemia + 100mcg de midazolam ; GV-PCI + 100mcg de midazolam. Após estabilização (t 0 ), e nos tempos t 5 , t 10, t 15 , t 20 e t 25 , foram registrados a FC, Fco, pressões sistólica (PS) e diastólica (PD) e dP/dt. A PD foi mantida em 5 ± 2 mmHg. Empregou-se método estatístico ANOVA e Teste de Tukey para p < 0,05. Resultados: Não ocorreram variações significantes entre FCo e FC. Na dP/dt, ocorreram diferenças (p<0,05) entre os grupos I e II (respectivamente 94,7±23,0 e 62,3±12,1%). O precondicionamento (GIII), melhorou significantemente os resultados do grupo II (respectivamente 62,3±12,1 e 87,1±12,4 %). A queda da dP/dt no grupo II não foi impedida pelo midazolam (GIV) ( 62,3±12,1 e 60,5±15,8 %). No grupo III a dP/dT foi 87,1±12,4%, sendo que no grupo V, apenas 55,5±17,2% (p<0,05). Conclusão: O midazolan quando administrado antes da isquemia não impediu...
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