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.