Centrally administered ouabain aggravates rapid-eye-movement-sleep-related bradyarrhythmias in freely moving rats.

1. The effects of continuous infusions of ouabain on bradyarrhythmias (cardiac pauses for 0.5 s or longer) during sleep were examined in freely moving Wistar-Kyoto rats. 2. In a control group (n = 7), saline was infused into both the lateral ventricle and the femoral vein. In an intracerebroventricular (i.c.v.) ouabain group (n = 7), ouabain was infused centrally, such that each rat received three stepped doses of 1, 10, and 100 ng kg-1 h-1 for 3 days at each dose, while saline was infused systemically. In an intravenous (i.v.) ouabain group (n = 7), ouabain was infused systemically at the same doses as the i.c.v. ouabain received, while the simultaneous i.c.v. infusion of saline was carried out. 3. Three-day i.c.v. infusions of the three stepped doses of ouabain caused a dose-dependent increase in the frequency of bradyarrhythmias during rapid-eye movement (REM) sleep without affecting the time spent in REM sleep, arterial pressure, average heart rate, or the frequency of bradyarrhythmias during non-REM sleep. Intravenous ouabain or i.c.v. saline had no effects on the frequency of bradyarrhythmias. 4. Intrinsic CNS activity during REM sleep may be involved in the centrally mediated arrhythmogenic properties of ouabain during sleep.