OUABAIN CARDIOTOXICITY IS ENHANCED BY GABA IN ANESTHETIZED RATS

Potential alteration of ouabain-induced cardiotoxicity by gamma-aminob utyric acid (GABA) in rats was tested by infusing ouabain for 10 min ( 0. 7 mg/kg/min, i.v.) before or after continuous infusion of Ringer's solution with or without GABA (1 mg/min, i.v.). GABA evoked hypotensio n and bradycardia of similar magnitude under both conditions. The inci dence of ouabain-induced ventricular fibrillation (VF) or cardiac arre st (CA) was similar in both groups. However, the time intervals to ons et of VF and CA, in rats given ouabain before, but not after, GABA wer e shorter than in rats treated with Ringer's solution (p < 0.05). In e xperiments where baclofen (0.034 mg/min, i.v.) was infused after ouaba in, hypotension and bradycardia occurred, but the incidence and times of ouabain-induced VF and CA were similar to control values. These res ults suggest that the enhancement in ouabain cardiotoxicity was mediat ed by GABA(A) receptors.