[Effect of diazepam on myocardial contraction and on the response to dopamine. Study in isolated rat hearts]. / Efeito do diazepam na contratilidade miocárdica e na resposta à dopamina. Estudo em corações isolados de ratos.

PURPOSE: The myocardial contractility variations and the cardiac rate were studied in isolated hearts of rats with injection of diazepam, dopamine and the association of both. METHODS: In all animals, after anesthesia, the hearts were removed and perfused with Krebs-Henseleit solution enriched by 95% O2 under a constant pressure of 90 cm H2O, until complete stabilization, for control value recordings. The following groups were studied: I) ten hearts: after stabilization the control values were recorded and dopamine (3 micrograms/ml) injected; IIA and IIB): also ten hearts were used and submitted to 50 micrograms and 100 micrograms of diazepam injections respectively. III) ten hearts studied with 50 micrograms of diazepam and 3 micrograms/ml of dopamine injection in a sequential form. RESULTS: Myocardial contractility arose in group I, from 37 g.seg-1 (control mean-value) to 70 and 53 g.seg-1 (1st and 3rd min); p < 0.001. In the groups IIA and IIB the dT/dt fell considerably in relation to the control: 35 g.seg-1 to 24 and 30 g.seg-1 (1st and 3rd min)--group IIA; p < 0.001 -32 g.seg-1 to 22 and 25 g.seg-1 (1st and 3rd min)--group IIB; p < 0.001. In the group III, a partial inhibition of the inotropic effects of dopamine by the injection of diazepam was observed. Heart rate follows fully the dT/dt variations in the groups IIA, IIB and III. CONCLUSION: Diazepam presents inotropic and chronotropic negative effects with the 50 micrograms as well as with 100 micrograms injection and the chronotropic and inotropic effect of dopamine (3 micrograms) injection was partially inhibited by the previous injection (50 micrograms) of diazepam.

Reversäo pelo flumazenil do efeito cardiodepressor induzido pelo diazepam / Reversal by flumazenil of the cardiodepressant effect induced by diazepam

Foram estudados em sete ratos de raça wistar os efeitos do antagonista dos receptores GR (centrais). Flumazenil (8-fluoro-1,6-dihidro-5-metil-5-fenil-2h-1,4-benzodiazepina-3-carboxilato de etila) nas concentrações de dez mcg/ml, na depressÒo miocßrdica induzida pelo Diazepam (7-cloro-1,3-dihidro-1-metil-5-fenil-2h-1,4-benzodiazepin-1-ona) em doses de 100 mcg/ml em coraçöes isolados de ratos. Nestes experimentos foi utilizado o mÚtodo de LANGENDORFF e tÚcnica de GOTTLIEB e MAGNUS, modificada por PITCHON, utilizando como perfusato a soluçÒo de Krebs-Henseleit. Podemos constatar que nesta experimentaçÒo, o Flumazenil foi capaz de antagonizar os efeitos cardioinibidores do Diazepam. Estas açöes nos levam a sugerir a presença de receptores Gabarelacionados nos coraçöes isolados estudados.